# Setting up my Lithium connections



## DIYguy (Sep 18, 2008)

spdas said:


> Aloha, all. Please advise me what to buy or materials to use and where to get it for installing my 44 x 200ah (160ah case) TS cells that I am installing to get rid of the 14 lead optimas in my Toy Yaris.


First of all 14 x 12 volt optimas = 168 volts. 44 * 3.2 volt TS = 140 volts. Hope that is not an issue.


spdas said:


> 1: I currently have 10xoptimas in the rear and will put 22 TS 200's there. What ready made - to + straps do I need and where to buy-OR-what materials and gauge, tools, etc. do i use to make them?


Interconnecting bars are available where you bought your batteries I expect.


spdas said:


> I will be charging 22 cells at a time, 22 in back and 22 in front. And want one charging point in rear. What size charging wire do I need to run from back to front to carry [email protected] max? #8, 6?


How do you get 80volts and 50 amps? I suspect both numbers are low....???? Go to your local welding supply store and buy 2/0 welding cable and lugs with suitable hole sizes for connections. You may need to borrow/rent/buy a crimper.


spdas said:


> 2: What gauge wire do i need to join the front and rear pack? (I probably already have it though for the current lead)


As above...2/0 welding cable.


spdas said:


> 3: In front I will have 11 cells just behind the bumper and 11 cells up near the firewall.
> suggestions?


Just confused about your pack voltage and expected current draw. You should expect several hundred amps to get rolling and then perhaps as low as 50 for maintaining lower speeds. 80 volts??


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## spdas (Nov 28, 2009)

DIYguy said:


> First of all 14 x 12 volt optimas = 168 volts. 44 * 3.2 volt TS = 140 volts. Hope that is not an issue.


My charger is a charge controller running off of 12x200W solar panels and will put out 80v @ 40-50amps so to charge 22 cells @ 3.6V=79.20. I can go more cells to equal 80v if charging the TS cells at 3.5 is better? (23 cells) 


> Interconnecting bars are available where you bought your batteries I expect.


I bought the cells used so no accessories.



> How do you get 80volts and 50 amps? I suspect both numbers are low....???? Go to your local welding supply store and buy 2/0 welding cable and lugs with suitable hole sizes for connections. You may need to borrow/rent/buy a crimper.


I am charging up to 160v and having to split charging into 2 so that is how i get the 80v. 3.6v per cell.
All the cabling is 2/0 for the Lead packs, so I will use as much as this for the Lithium and probably only need to make/order buss bars.


> Just confused about your pack voltage and expected current draw. You should expect several hundred amps to get rolling and then perhaps as low as 50 for maintaining lower speeds. 80 volts??


On mild accelleration I use up to 200amp and cruising at 40mph I use 50amp, that is with the lead optimas.


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## DIYguy (Sep 18, 2008)

# 8 wire should be fine.

Any of the battery suppliers could get them for you. You may want to call around first so you don't wait for a shipment from china. Some folks have made their own from copper or even aluminum.

I hope you don't mind waiting for your car to charge... lol


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## Tahoe Tim (Feb 20, 2010)

DIY,
I'll bet his lead pack sags well below 140v so I am guessing he will be fine on that issue.


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## Guest (Jan 20, 2011)

You will still need a charge algorithm for your charge controller to charge your batteries. If you only are getting 80V DC then you'd need a way to bump the voltage and lower the amps to get the voltage you need. At 80 volts you will only charge to 80 volts. How are you going to up the voltage and how are you going to control the charge algorithm? You can't just plug into an outlet and let them charge with no control. I am hoping your putting your solar into a static battery bank and if so you can use an inverter to power your home and a proper charger like an Elcon that can charge to the proper voltage limits and amp limits you need. 

Do you have your batteries yet? TS should provide interconnects with your cells if I am not mistaken. Yes, 2/0 cable. Is your controller able to run at a lower voltage? 

Pete


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## EVfun (Mar 14, 2010)

I really don't recommend charging with the pack split into two parallel packs and discharging those two packs in series. It is very hard to insure that charging current splits evenly and this is important with Lithium because the charge voltage curve is so shallow until the very end. There is no reason to charge more than just slightly into the top end of the voltage curve so it will be difficult to insure the packs both get equally full.


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## GizmoEV (Nov 28, 2009)

I would recommend that you get a fine wire stainless steel brush to clean off the top of the posts just before making your connections. You should also put some NOALOX or NO-OX-ID on your connections too. Aluminum oxide has a high resistance and happens quite rapidly.

For buss bars you could have a sheet metal shop make some out of several layers of copper sheet with a bend in the middle. You can see a picture of what came with my TS cells on my blog. You can also read what I did to prepare my posts here.

Do you have an Ah counter of some sort? If not I'd recommend the CycleAnalyst. Get the large display high voltage version. I have a picture of how I mounted it here. It is a very reasonably priced meter and worth every penny. You need to know how much energy you are using.


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## ElectriCar (Jun 15, 2008)

Let me chime in that it would be better if you can afford it to run 4/0 cable for connecting the front and back halves and to tie in to the controller. That way at higher currents you won't be wasting voltage heating your wire. Wire has resistance and higher currents will create more voltage loss which will appear as sag. 1C for your cells is 200 amps and I sometimes draw near 400. However is you have a Gizmo type vehicle that is light weight and you have no desire to race etc 2/0 would be fine.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> Let me chime in that it would be better if you can afford it to run 4/0 cable for connecting the front and back halves and to tie in to the controller. That way at higher currents you won't be wasting voltage heating your wire. Wire has resistance and higher currents will create more voltage loss which will appear as sag. 1C for your cells is 200 amps and I sometimes draw near 400. However is you have a Gizmo type vehicle that is light weight and you have no desire to race etc 2/0 would be fine.


Perhaps 4/0 from controller to motor where current can be higher...but the rest should be more than adequate at his amperage levels. (I did exactly what you suggest though... then again, I have a Soliton1  )


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## DIYguy (Sep 18, 2008)

EVfun said:


> I really don't recommend charging with the pack split into two parallel packs and discharging those two packs in series. It is very hard to insure that charging current splits evenly and this is important with Lithium because the charge voltage curve is so shallow until the very end. There is no reason to charge more than just slightly into the top end of the voltage curve so it will be difficult to insure the packs both get equally full.


This is a good point. Perhaps instead of charging them separately, (which I think is the intention...??) the two packs could be paralleled for charging all at the same time @ 80volts. This should keep them all the same... yes/no?


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## ElectriCar (Jun 15, 2008)

DIYguy said:


> Perhaps 4/0 from controller to motor where current can be higher...but the rest should be more than adequate at his amperage levels. (I did exactly what you suggest though... then again, I have a Soliton1  )


Bragger! I have parallel 1/0 throughout my pack and most under the hood which is electrically equal to 4/0. I have no way to measure my motor current but I think it must hit 500A at times because I never quite make it to 400 battery amps. Most ever on kw meter was 46 at about 122V I think and then I was only trying to see what I could max out at. Either that or I don't have enough voltage to force enough current through the motor. That should be remedied in about 6 weeks or so when I get my pack installed. However with other additions ie cycle analyst, voltage relays, new tach etc it may take longer. If I did [email protected] sag free volts I'd be looking at 60ish kw!

BTW where is your new pack? I'm due 20th or so Feb.


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## EVfun (Mar 14, 2010)

ElectriCar said:


> Let me chime in that it would be better if you can afford it to run 4/0 cable for connecting the front and back halves and to tie in to the controller. That way at higher currents you won't be wasting voltage heating your wire. Wire has resistance and higher currents will create more voltage loss which will appear as sag. 1C for your cells is 200 amps and I sometimes draw near 400. However is you have a Gizmo type vehicle that is light weight and you have no desire to race etc 2/0 would be fine.


I really think this is getting carried away. Typical running currents do not exceed 200 amps for most EVs. If you can replace 20 feet of 2/0 cable with 4/0 cable the savings will be less than 1/8 of a volt at 200 amps. If you are running a 120 volt system that amounts to less than 1/10 of 1% in a 120 volt EV. For the few seconds you draw 1000 amps (if you batteries and controller are both capable) the voltage drop is almost 0.6 volts for an efficiency loss of about 1/2 of 1%.

Even if you compare between 20 feet of 1/0 cable and 4/0 cable the difference is not great. At 200 amps the additional voltage drop is about 0.2 volts and at 1000 amps it is about 1 volt. If you regularly hit 1000 amps in a street vehicle I don't recommend 1/0 because you can make it warm. I do recommend the motor loop be wired one step larger than the battery loop (1/0 and 2/0 is typical for me) because the controller can make motor current higher than the battery current (at lower than pack voltage on the motor) but will never make the motor current lower than the battery current.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> Bragger! I have parallel 1/0 throughout my pack and most under the hood which is electrically equal to 4/0. I have no way to measure my motor current but I think it must hit 500A at times because I never quite make it to 400 battery amps. Most ever on kw meter was 46 at about 122V I think and then I was only trying to see what I could max out at. Either that or I don't have enough voltage to force enough current through the motor. That should be remedied in about 6 weeks or so when I get my pack installed. However with other additions ie cycle analyst, voltage relays, new tach etc it may take longer. If I did [email protected] sag free volts I'd be looking at 60ish kw!
> 
> BTW where is your new pack? I'm due 20th or so Feb.


Sorry for braggin... lol (BTW, I've done 1000 amps sag'd to 160 volts (from 205 or so)  )
Pack is on the ship. Arrives in Vancouver on the 25th and Toronto on the 7th.


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## DIYguy (Sep 18, 2008)

EVfun said:


> I really think this is getting carried away. Typical running currents do not exceed 200 amps for most EVs. If you can replace 20 feet of 2/0 cable with 4/0 cable the savings will be less than 1/8 of a volt at 200 amps. If you are running a 120 volt system that amounts to less than 1/10 of 1% in a 120 volt EV. For the few seconds you draw 1000 amps (if you batteries and controller are both capable) the voltage drop is almost 0.6 volts for an efficiency loss of about 1/2 of 1%.
> 
> Even if you compare between 20 feet of 1/0 cable and 4/0 cable the difference is not great. At 200 amps the additional voltage drop is about 0.2 volts and at 1000 amps it is about 1 volt. If you regularly hit 1000 amps in a street vehicle I don't recommend 1/0 because you can make it warm. I do recommend the motor loop be wired one step larger than the battery loop (1/0 and 2/0 is typical for me) because the controller can make motor current higher than the battery current (at lower than pack voltage on the motor) but will never make the motor current lower than the battery current.


For most, yes. Mine is just right. I have 2/0 between batteries, 4/0 for long runs and 4/0 from motor to controller. I have had both the 2/0 and the 4/0 to motor pretty darn warm.  I wouldn't change it for sure. But yes, for most, it's true. . .and if it aint gettin warm, u don't need to change it.


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## EVfun (Mar 14, 2010)

DIYguy said:


> This is a good point. Perhaps instead of charging them separately, (which I think is the intention...??) the two packs could be paralleled for charging all at the same time @ 80volts. This should keep them all the same... yes/no?


Could we deliberately insert a precision (0.01%) 1/2 ohm resistor in each half? The thing is, just 0.01 volt differences in per cell voltage represent quite a difference in SOC in that great middle range. I wonder if leaving the pack halves in parallel could allow them to equalize? 

Well, that question brings up a big question I've had. If a big bunch of cells where all placed in parallel (say 40, 100 amp hour cells) making one giant 3.2 volt 4000 amp hour battery would the cells all reach the same state of charge if left in parallel? What would happen if all the cells where right in the middle of their resting voltage range at 3.29 to 3.31 volts each at the start? How long might that take? It would seem that even a few microvolts would slowly move charge if given some time since there is no significant current flow to cause wiring voltage drop issues.


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## DIYguy (Sep 18, 2008)

EVfun said:


> Well, that question brings up a big question I've had. If a big bunch of cells where all placed in parallel (say 40, 100 amp hour cells) making one giant 3.2 volt 4000 amp hour battery would the cells all reach the same state of charge if left in parallel? What would happen if all the cells where right in the middle of their resting voltage range at 3.29 to 3.31 volts each at the start? How long might that take? It would seem that even a few microvolts would slowly move charge if given some time since there is no significant current flow to cause wiring voltage drop issues.


Yes, they should all equalize. This is how to balance a new pack. Best to feed charger from two "sides" of the circuit perhaps even one tie in the middle...but yes, they should all equalize.


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## ElectriCar (Jun 15, 2008)

EVfun said:


> I really think this is getting carried away. Typical running currents do not exceed 200 amps for most EVs. If you can replace 20 feet of 2/0 cable with 4/0 cable the savings will be less than 1/8 of a volt at 200 amps. If you are running a 120 volt system that amounts to less than 1/10 of 1% in a 120 volt EV. For the few seconds you draw 1000 amps (if you batteries and controller are both capable) the voltage drop is almost 0.6 volts for an efficiency loss of about 1/2 of 1%.
> 
> Even if you compare between 20 feet of 1/0 cable and 4/0 cable the difference is not great. At 200 amps the additional voltage drop is about 0.2 volts and at 1000 amps it is about 1 volt. If you regularly hit 1000 amps in a street vehicle I don't recommend 1/0 because you can make it warm. I do recommend the motor loop be wired one step larger than the battery loop (1/0 and 2/0 is typical for me) because the controller can make motor current higher than the battery current (at lower than pack voltage on the motor) but will never make the motor current lower than the battery current.


No, not getting carried away. I said if he can afford it, it would be wise unless he's driving something like I described that doesn't draw many amps. I did some calculations recently for someone running 1000A on 2/0. The voltage drop in wire is proportional to the length. The calculation I did was for 80 feet of wire and the voltage drop was 6.4V. That equates to two batteries being wasted heating wire, same as internal resistance in batteries. 40' would be 3.2V. Jumping to 4/0 dropped it down a good bit but don't recall how much. The 80' was for example purposes because that equates to a 2 cell drop in voltage at 1000A. My wiring in an S10 adds up to about a 65' loop. 

If you're pulling 1000A you're either moving a large vehicle or racing etc. If that's the goal then I would go with even larger wire or parallel smaller ones for an equivalent larger size. IMO there's no reason not to other than money. Why lug around one or two more batteries if you're just going to waste the capacity on heating under sized wiring??? Skip the weight and spend the money on larger wire. The wire would only add a few pounds compared to additional batteries and would free up space.


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## EVfun (Mar 14, 2010)

DIYguy said:


> Yes, they should all equalize. This is how to balance a new pack. Best to feed charger from two "sides" of the circuit perhaps even one tie in the middle...but yes, they should all equalize.


I'm curious is they would equalize if the charging was omitted. Just parallel a bunch of cells as received (about 1/2 full) and wait for some period of time.


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## DIYguy (Sep 18, 2008)

EVfun said:


> I'm curious is they would equalize if the charging was omitted. Just parallel a bunch of cells as received (about 1/2 full) and wait for some period of time.


Yep... that way too... Parallel and wait a bit. They're all gonna be the same.


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## GizmoEV (Nov 28, 2009)

ElectriCar said:


> If you're pulling 1000A you're either moving a large vehicle or racing etc.


Or running low voltage. To drive my Gizmo at 49-50mph (wide open ) the batteries are putting out ~125A. Climbing my hill to get home I see 150A minimum up to 230A. The original 4 gauge wire would be warm after the hill climb. I went to 1 gauge and now it doesn't get warm and I gained a whole 3-4mph top end speed and 2-3mph hill climbing speed (when running my 48V lead acid pack.) I don't want to go back to see what it would be like now so I won't be testing it. On a full throttle acceleration battery current peaks at a little over 400A.


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## EVfun (Mar 14, 2010)

ElectriCar said:


> No, not getting carried away. I said if he can afford it, it would be wise unless he's driving something like I described that doesn't draw many amps. I did some calculations recently for someone running 1000A on 2/0. The voltage drop in wire is proportional to the length. The calculation I did was for 80 feet of wire and the voltage drop was 6.4V. That equates to two batteries being wasted heating wire, same as internal resistance in batteries. 40' would be 3.2V. Jumping to 4/0 dropped it down a good bit but don't recall how much. The 80' was for example purposes because that equates to a 2 cell drop in voltage at 1000A. My wiring in an S10 adds up to about a 65' loop.


Whoa, I've built 3 EVs and haven't used 80 feet of cable in them combined! Remember how little time you spend at 1000 amps before sizing for it. Even a 200 amp hour pack can't spend 5 minutes per charge at 1000 amps! At a more realistic 30 feet and 300 amps you are down to less than 1 volt. It rises to about 2.5 volts at 1000 amps, normally only seen for a couple seconds when you're seriously gettin' on it.

My Buggy features 1/0 cable except for the motor loop is 2/0. The VW Pickup was built with 1/0 except the front pack to rear pack cables and motor loop where 2/0. The Datsun uses 1/0 except for the motor loop is 2/0. The Lithium in the Buggy reconversion will feature 1/0 except the motor loop will retain the existing 2/0 cable. I'm pretty sure even John Wayland's Blue Meanie only features 1/0 in the battery loop (no idea what runs under the car from the rear pack to the front.)

There is nothing wrong with using larger cable, it's mostly just a few extra pounds. There is a slight reduction in voltage drop, but in most cases the trip efficiency gains will be under 1%. With todays copper prices I can't recommend it (add another cell for about the same weight.)


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## ElectriCar (Jun 15, 2008)

EV, a quick calculation follows. I've 24 batteries with an 8" jumper between them. That is 15' right there. Add about 4' for the tie between the three battery boxes in the back, about 25' getting to the back and back to the front, about 10-12' coursing underneath the hood to the motor & back, through the disconnect etc, and I've got nearly 60' right there in my S10. 

I did a quick calculation at 200A comparing 2/0 to 4/0 cable. A 65' trip yields 1.001V drop on 2/0 and .65V on 4/0, a 35% savings. At 400A climbing a hill for 10 sec or so and it doubles to 2V, or nearly 1 lithium cell worth of voltage. Not a terrible lot but for a little more expense I can save 35% of that and get a little more oomph, more than the small savings would appear to contribute. 

Here's a tidbit of data to show how significant a small voltage drop affects overall power. I learned this after moving into a new home where the electrician skimped on wire. I've been an electrician for 30 years and didn't realize this. 

I noticed a space heater wasn't putting out near the heat it did in my other home. Investigation revealed the voltage dropped to 110 from 120V upon energizing the heater, *a 9% drop. However the resulting power output dropped 30% *from the rated 1500W at 120V down to 1050W at 110V. Doesn't make sense but if you do the calculations, that's what it is. 

I also boosted the voltage on a heater at work rated 4000W on 240V from 208 to 232V, +11.5%. The power output went from 3000W to about 3700W, about 23% improvement!


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## spdas (Nov 28, 2009)

EVfun said:


> I really don't recommend charging with the pack split into two parallel packs and discharging those two packs in series. It is very hard to insure that charging current splits evenly and this is important with Lithium because the charge voltage curve is so shallow until the very end. There is no reason to charge more than just slightly into the top end of the voltage curve so it will be difficult to insure the packs both get equally full.


Aloha, to end the confusion I caused, I will have 44 cells in series to make 160v at full charge of 3.6 each or 141 at 3.2 each. My electronic MPPT charge controller being fed by my solar panels has a kajillion computerized settings for voltage/amperage/time/percentage etc etc. But it only charges up to 80v, so I will be charging 1/2 the pack at a time. The charge controller is computerized and samples the sun strength and optimizes voltage vs. amperage. It is capable of setting voltage 10v to 80v 1/10th of a volt at a time as well as regulating amperage and percentage of charge and time and temp of batteries. When the controller throttles down to say 3-4 amps (or arbetraly to .1V) to indicate a full charge then I will use a A-B battery switch to charge the 2nd 22 cells in series. (I am waiting for Outback or Morningstar or Xantrex to make 160v controller and i will be the first to buy it). In the meantime I will get a free charge that should take about 6 hours on a sunny day. but as you know sun does not shine often in Hawaii on the leeward coast!! Ya right. BTW. all the battery cables are "Yaris electric 600v 2/0 www.tristar.com" and the longest length from the rear to the controller in front is 8.5 feet.

francis


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## EVfun (Mar 14, 2010)

ElectriCar said:


> I did a quick calculation at 200A comparing 2/0 to 4/0 cable. A 65' trip yields 1.001V drop on 2/0 and .65V on 4/0, a 35% savings.


That is one way of measuring your savings, but look at what the controller "sees." With the 2/0 you get about 135 volts at 200 amps while the 4/0 delivers about 135.35 volts at 200 amps. That is about 1/4 of 1% more efficient. 

A significant voltage drop is a more serious issue for a space heater because it is a resistive load. The reduced voltage causes a proportional drop in current. The heat output roughly tracks the voltage squared.


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## EVfun (Mar 14, 2010)

spdas said:


> Aloha, to end the confusion I caused, I will have 44 cells in series to make 160v at full charge of 3.6 each or 141 at 3.2 each. My electronic MPPT charge controller being fed by my solar panels has a kajillion computerized settings for voltage/amperage/time/percentage etc etc. But it only charges up to 80v, so I will be charging 1/2 the pack at a time. The charge controller is computerized and samples the sun strength and optimizes voltage vs. amperage. It is capable of setting voltage 10v to 80v 1/10th of a volt at a time as well as regulating amperage and percentage of charge and time and temp of batteries. When the controller throttles down to say 3-4 amps (or arbetraly to .1V) to indicate a full charge then I will use a A-B battery switch to charge the 2nd 22 cells in series. (I am waiting for Outback or Morningstar or Xantrex to make 160v controller and i will be the first to buy it). In the meantime I will get a free charge that should take about 6 hours on a sunny day. but as you know sun does not shine often in Hawaii on the leeward coast!! Ya right. BTW. all the battery cables are "Yaris electric 600v 2/0 www.tristar.com" and the longest length from the rear to the controller in front is 8.5 feet.
> 
> francis


If you set the charger up with a tight voltage control that doesn't drift and shut it off based reaching a tightly controlled low current you should be O.K. Perhaps something like 79.2 volts +/- 0.1 volt and 0.5 amp +/- 0.05 amp should be pretty dang close. With split charging I would recommend some type of LVC detection (yes, some type of battery monitoring system) so you can shut down if one half ends up going flat first.


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## DIYguy (Sep 18, 2008)

Still think it may be a good idea to do your charge the two sub-packs in parallel mode. This way there is no worries of differences as well as not having to tend it to change over pack charging from one half to the other. Shouldn't be too hard to set up.


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## spdas (Nov 28, 2009)

DIYguy said:


> Still think it may be a good idea to do your charge the two sub-packs in parallel mode. This way there is no worries of differences as well as not having to tend it to change over pack charging from one half to the other. Shouldn't be too hard to set up.


I think charging in parallel is the best too. And it saves me remembering to switch to charge the second bank. But on the other hand, the charger throttles down to .01 amps so both packs should be charged the same at the end of charge. And I loose the advantage if one cell is somehow defective, both packs of the parallel charging setup may be hurt, whereas only one pack is by charging individually. 

What are your ideas for a fool proof method of charging in parallel? The only way I can come up with is using a large Anderson connector to split the pack in half then use smaller Siamese Anderson connectors to charge each pack.


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## EVfun (Mar 14, 2010)

DIYguy said:


> Still think it may be a good idea to do your charge the two sub-packs in parallel mode. This way there is no worries of differences as well as not having to tend it to change over pack charging from one half to the other. Shouldn't be too hard to set up.


I would agree with you. I would still suggest choosing a cut-off current that is very low so the differences in state of charge caused by wiring are minimized. I would also recommend some type of LVC monitoring or Lee Hart style battery bridge because it could detect if one half didn't get as much charge before damage is done.


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## spdas (Nov 28, 2009)

EVfun said:


> I would agree with you. I would still suggest choosing a cut-off current that is very low so the differences in state of charge caused by wiring are minimized. I would also recommend some type of LVC monitoring or Lee Hart style battery bridge because it could detect if one half didn't get as much charge before damage is done.


Since my experience is with charging FLA and AGM's, and I know Bulk, Absorb, Float algo's. Do you not charge higher than the expected end voltage, ie @ 3.9 to get 3.6, or do you charge 3.6 to get 3.6? 

Then to charge a 3.2 battery to 90% what should I charge to? 3.5, 3.55? 

Will Lithium provide a similar resistance as AGM's to throttle down the amperage?

thanks francis


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## DIYguy (Sep 18, 2008)

spdas said:


> I think charging in parallel is the best too. And it saves me remembering to switch to charge the second bank. But on the other hand, the charger throttles down to .01 amps so both packs should be charged the same at the end of charge. And I loose the advantage if one cell is somehow defective, both packs of the parallel charging setup may be hurt, whereas only one pack is by charging individually.
> 
> What are your ideas for a fool proof method of charging in parallel? The only way I can come up with is using a large Anderson connector to split the pack in half then use smaller Siamese Anderson connectors to charge each pack.


Just get a couple of these
http://t0.gstatic.com/images?q=tbn:ANd9GcSWPPu0qrMUR-nHjw2fGRnkmqQMDtwUrLaioZXtZAXCsZ9hve4nxA
and control the low voltage with an interlock in your charge plug. Then u don't have to remember anything. If your charger is not temperature compensated and you charge packs at different temperatures, there may be some influence there also.... ??


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## DIYguy (Sep 18, 2008)

spdas said:


> Since my experience is with charging FLA and AGM's, and I know Bulk, Absorb, Float algo's. Do you not charge higher than the expected end voltage, ie @ 3.9 to get 3.6, or do you charge 3.6 to get 3.6?
> 
> Then to charge a 3.2 battery to 90% what should I charge to? 3.5, 3.55?
> 
> ...


For TS, you could charge to 3.8 for Calb probably 3.45 or 3.5 at most. (not using HVC that is) Lithium curves are actually less complicated. The typically go in CC mode to the knee of the curve and CV to finish off. CV the whole way would probably work fine but just take a lot longer. Others may chime in on this one.


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## EVfun (Mar 14, 2010)

spdas said:


> Since my experience is with charging FLA and AGM's, and I know Bulk, Absorb, Float algo's. Do you not charge higher than the expected end voltage, ie @ 3.9 to get 3.6, or do you charge 3.6 to get 3.6?
> 
> Then to charge a 3.2 battery to 90% what should I charge to? 3.5, 3.55?
> 
> Will Lithium provide a similar resistance as AGM's to throttle down the amperage?


Lithium has a very flat charge curve so the voltage slowly climbs to about 3.45 volts per cell (vpc.) Past that point the cell is 95+% full and the end of charge ramp is quick when it starts. There is no reason to fully charge Lithium every cycle, in fact full charges slightly shorten cycle life. The cells start taking immediate damage if they exceed 4.2 volts (or so.) So the goal tends to be just getting into the end voltage range so you can determine they have been charged to near full (perhaps 98% full) but not letting it go to high on any cell. The current will drop to nearly zero as a steady voltage, more so than with good AGM lead. I think they are actually easier to charge, you just need to avoid overcharging (and over-discharging in use.)


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## GizmoEV (Nov 28, 2009)

By my rough measurements, hand recording meter readings and stop watch times, on a TS-LFP100AHA cell that there is only about 1Ah from 3.45V to 3.65V and less than a third of an Ah from 3.5V to 4V. I'm now only charging my TS pack to an average of 3.485vpc. Once my charger starts to back off on the current it only takes 10-15 minutes to reach the end of charge cutoff voltage. This is with a 120VAC Zivan NG1 charging a 200Ah pack of 20 cell pairs.

As to charging the two half packs separately or together. I'd recommend charging them in parallel so that you can end the charge at any time and know the two half packs are at essentially the same capacity. The last thing you want is to have a need to go somewhere and only have half the pack charged.


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## spdas (Nov 28, 2009)

GizmoEV said:


> By my rough measurements, hand recording meter readings and stop watch times, on a TS-LFP100AHA cell that there is only about 1Ah from 3.45V to 3.65V and less than a third of an Ah from 3.5V to 4V. I'm now only charging my TS pack to an average of 3.485vpc. Once my charger starts to back off on the current it only takes 10-15 minutes to reach the end of charge cutoff voltage. This is with a 120VAC Zivan NG1 charging a 200Ah pack of 20 cell pairs.


Wow not much current at the top!!! Do you have AH data for other voltages under 3.5v down to say 20% SOC? thanks
francis


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## GizmoEV (Nov 28, 2009)

I have one where I started at 3.30V. Unfortunately I didn't record what my ending current was to get a cell to 3.30V. IIRC, I discharged a cell below 3.30V far enough that the voltage didn't suddenly jump to 3.30v so that I could let my CC/CV powersupply bring the battery up to 3.30v. I very likely left it for several hours so the current had dropped to under 100mA. I started charging and recording time, voltage, and current. 935 minutes later I stopped the charge at 3.451V at 476mA. The energy came out to 66.0Ah.

I sure do wish I had a recording device to do this. Naturally I didn't repeat the experiment. I had to get my pack into my rig!


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## EVfun (Mar 14, 2010)

GizmoEV said:


> By my rough measurements, hand recording meter readings and stop watch times, on a TS-LFP100AHA cell that there is only about 1Ah from 3.45V to 3.65V and less than a third of an Ah from 3.5V to 4V. I'm now only charging my TS pack to an average of 3.485vpc. Once my charger starts to back off on the current it only takes 10-15 minutes to reach the end of charge cutoff voltage. This is with a 120VAC Zivan NG1 charging a 200Ah pack of 20 cell pairs.


Now this is learning time. I have been charging my 60 amp hour TS cells to 3.65 vpc (146 volts for 40) and holding that for 1 hour using a Manzanita Micro PFC-20. I cannot accurately measure current at the end because I'm using the cars 500 amp shunt, but it appears to be about 1 amp (I get a 0.1 mv reading on my old Fluke 70-3.) I need to get a 0.01 ohm resistor to use as a charging shunt in order to get accurate numbers but it hasn't been a priority. 

What charging time and rate where you seeing between 3.45 and 3.65 volts, and at what was charging rate at the charge cut-off? I'm pretty sure that 3.65 volts at nearly zero current is essentially fully charged and I'm trying to get a feel for how much is being left on the table. If it is one amp hour at a sufficiently low rate then it may be only slightly more than one amp hour below absolutely full. 

I don't mind leaving about 2 or perhaps 3 amp hour on the table, but don't want to give up to much because that means every discharge is that much deeper. I've mostly been playing around in the middle and would like to lower my charge voltage to about 3.5 vpc (140 volts) if it doesn't leave much on the table. I know some of the CALB users are doing that but I haven't heard as much about low finish charge voltages with TS cells.


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## spdas (Nov 28, 2009)

Looking at the thundersky manual for the LFP battery, I notice optimum charging at .5CA and at 93% of the knee, we are at 4.30v. Not the 3.5v or so volts many here are recommending. At 3.5v TS says the cell is 60% charged. Whats up? 

Francis


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## GizmoEV (Nov 28, 2009)

Here is the basic setup I did. It looks like I did 5 test runs the last two of which I "ran together" meaning I charged to a particular voltage and current and then cranked up the current for the second half. IIRC, for all but the very last setup I discharged the cell well below my starting voltage so that when I hooked up the cells to my BK Precision 1761 Power Supply and cranked up the current it would take a while to reach the desired starting test voltage. I did this to be sure I wasn't actually starting at a voltage over my start voltage. This power supply displays current to the nearest 0.001A and I used an Extech Instruments DMM which reads to the nearest 0.001V connected to the battery terminals. I didn't use the power supply's voltage because I didn't want the voltage drop in the charging lines to affect my voltage reading. I set the max voltage on the power supply and let the current taper down to a few mA before starting my test.I used the stop watch on my watch for time and I did my best to observe and record the voltage and current at different intervals, usually one minute in length until the voltage and current didn't change very much between readings.

To calculate Ah I used average current divided by time in hours. For example on my 3.600-4.000V test the first reading was 3.600V at 3.486A, one minute later the reading was 3.830V at 2.000A. The formula I used was (3.486+2.000)/2*(1-0)/60=0.0457Ah. Naturally this is what I used in a spreadsheet and I didn't manually calculate each point. I'm not that bored 

These tests were done on a single TS-LFP100AHA LiFePO4 cell. I think, but am not sure, that this may have been the last shipment before the LiFeYPO4 cells. I know that tests 1-3 were on the same sell and likely tests 4 & 5 as well but I'm not sure. All the cells were from the same production run.

Test 1, January 2010
current before test start <100mA (very likely <25mA)
Start voltage: *3.600V*
Initial Current: 3.486
End voltage: *4.000V*
Ending current: 0.023A
Total Time: 142 minutes
Total Ah: 0.2213Ah

Test 2, January 2010
current before test start <100mA (very likely <25mA)
Start voltage: *3.542V*
Initial Current: 3.485
End voltage: *4.000V*
Ending current: 0.024A
Total Time: 140 minutes
Total Ah: 0.3550Ah

Test 3, January 2010
current before test start <100mA (very likely <25mA)
Start voltage: *3.397V*
Initial Current: 3.486
End voltage: *4.000V*
Ending current: 0.038A
Total Time: 85 minutes
Total Ah: 0.6588Ah

Test 4, July 14, 2010
current before test start <100mA (very likely <25mA)
Start voltage: *3.300V*
Initial Current: 3.507
End voltage: *3.451V*
Ending current: 0.476A
Total Time: 935 minutes (At 300 minutes the voltage had only risen to 3.339V so I stopped the charging, paralleled the two halves of my power supply and resumed the charging at 6.604A)
Total Ah: 66.0155Ah (This might be a little low because of the higher ending current. The "extra" is in the next test.)

Test 5, July 14, 2010
current before test start 476mA (I just cranked up the current at the end of the last test to continue this one so the Ah for this test might be a little high except that the ending current here isn't as low as in the first 3 tests.)
Start voltage: *3.451V*
Initial Current: 3.530
End voltage: *3.650V*
Ending current: 0.420A
Total Time: 55 minutes (minute 935-990 continuing from the previous test)
Total Ah: 1.0056 Ah

The last two tests had a significantly higher ending current than the first three tests. The most energy put into the battery after the current dropped below 500mA in the first three tests was 0.1436Ah in test #2 so I doubt the Ah count is very far from letting the current drop any lower.

All my cells are now in my battery pack so I'm not willing to pull one out and do more testing.  Hopefully someone else will verify my tests on other cells to give a better picture of actual capacity at various voltages.

I don't know how low of a current the Manzanita Micro PFC-20 can go to but I'm blessed with a Zivan which will cut back to zero current if necessary and it does every time if I let it finish the charge.

As for what is up with what TS says remember that 0.5C is 50A for a 100Ah cell. I have my cells in a 2p20s arrangement so a 200Ah pack and I'm ending at below 500mA. Even that is 0.005C for a 100Ah cell or 0.0025C for my 200Ah pack. Also, voltage is being measured at the cell terminals, not inside the cell. If you are charging at 0.5C to 4.30V and turn off the charger I'd guess the cell will come to rest at about 3.42V. I am guessing this by going back ~7Ah from the end on my data from test 5 & 4 above. Doing the same thing for the 60% figure I'd guess the resting voltage would be 3.335v.

It is very important to note the charging current when comparing cutoff voltages. My Zivan NG1 starts to cut back at somewhere around 68.5V or 3.425vpc. After 10-15min it has ramped back to under 500mA current. If I let it finish and time out after this point I've only seen my Kill-a-Watt meter record something less than 0.05kWh. I'll try to get a more formal check sometime but I don't remember much change in the energy out of the wall.

Wow, I think I'll post this to my Blog. It has been one of those write-ups I've been meaning to do.


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## spdas (Nov 28, 2009)

Thanks David for the above post. I am a little more confused and maybe you will clarify some points.

1: In your 5 tests Total AH are mostly below 1, but to me it seems to be 10x more. But in test 4 you state Total Ah: 66.0155Ah whereas other tests say Total Ah: 0.6588Ah and such. Are these typos or more my misunderstanding.

2: Commenting on TS says, you mentioned they charge to 4.30v and turning off the resting voltage may be 3.42v. Please clarify as I thought you charged without any leading voltage. ie. charge at 3.6 to end up at 3.6, not (as in AGM charge at 14.8v to end up around 13v)?

Here is the link to the PDF TS manual that was too big to upload here. I am sure everyone is familiar with it, but I need to clear up my understanding. Page 16 of the manual is the chart, but the whole manual is a good read.

http://evolveelectrics.com/Thunder Sky Lithium Batteries.html?gclid=CPvP8Nq2-J8CFSYbagodfGo7XA

Thanks for your help.
Francis


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## GizmoEV (Nov 28, 2009)

spdas said:


> 1: In your 5 tests Total AH are mostly below 1, but to me it seems to be 10x more. But in test 4 you state Total Ah: 66.0155Ah whereas other tests say Total Ah: 0.6588Ah and such. Are these typos or more my misunderstanding.


That isn't a typo. Note that in each test there is a start voltage and an end voltage. In test 4 it is from 3.300V to 3.451V and that it took 935 minutes or nearly 16 hours. The first three tests were to show how much energy there was from different start voltages to an ending voltage of 4.000V. Also note that the ending current is very low: 0.00038C to be precise. That is a long way from 0.5C.



> 2: Commenting on TS says, you mentioned they charge to 4.30v and turning off the resting voltage may be 3.42v. Please clarify as I thought you charged without any leading voltage. ie. charge at 3.6 to end up at 3.6, not (as in AGM charge at 14.8v to end up around 13v)?


If there is no voltage difference no current will flow. I set an upper voltage limit on my power supply and it would charge as fast as it could but not let the voltage get over the set point. It would cut back the current to keep from going over the set ending voltage. Because my ending current was so low the resting voltage after charge was very close to the number I gave. That is why it is important to know what the current is when a voltage is given. Charging to 4.00V is actually quite high and the cell will "relax" to a lower voltage. When I charge at such low currents to only 3.5vpc there is very little "relaxing" that happens. For example, my pack charges to 69.6-69.7V with a very low ending current. There is a very small load due to the DC-DC always on. In the morning when I go out the pack voltage will be around 68V. Even after sitting for two days the voltage will be between 67 and 68V. If I charged to 80V and came back in a day or two the voltage would be between 67 and 68V too. I would gain at best 1Ah of energy storage. See, it doesn't make sense to stress the cells by charging them to 4vpc when the ending current is rather low.

The TS manual you linked to is a 2007 copyright. I wouldn't go by that one. The one that came with my batteries is a 2009 copyright and it has lowered the max voltage to 4.25V. The more recent ones have lowered it even further to 4.0V. That should tell you something about the high voltage setting. As they have learned they have lowered it.

In any case, the graph you are referring to has three curves: Charge current, cell terminal voltage, and % of capacity or SOC%. Note that the charge current is 0.5C until the cell reaches its maximum rated voltage then the current is tapered back to avoid going over that point. Remember, however, that this voltage is only terminal voltage. The bigger the current flowing into or out of a cell the farther off the terminal voltage will be from the open circuit voltage of the cell. This is the same thing you see with your AGM batteries. TS says you can charge upto 3C until the cell is 80% full. I guarantee you will see a terminal voltage over 4V before the cell reaches 80% SOC. If you were to stop the current at that point the cell voltage would drop very rapidly at first and then settle down at a voltage representing 80% SOC. Also note that the current ramps down to near zero. My book shows this point at 0.015C. This would equate to 1.5A for a 100Ah battery or 3A for my 200Ah pack. The most my charger puts into the battery pack is ~15A or 0.075C. Even if I had a PFC-75 to charge with that would only be 0.375C. Why am I mentioning this? Unless you have a small pack you are unlikely to be charging it at 0.5C! I charge at such small rates that is why when my charger starts to cut back the current the pack is nearly full so it only takes a few minutes to top it off. The ending voltage is very close to the open circuit resting voltage because the current is so low.

Hope that clarifies a little.


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## spdas (Nov 28, 2009)

I will read through this a couple more times, but one thing strikes me in Test 3. How can you raise the voltage from 3.39 to 4v by adding only .6588ah into a 100ah cell? I see starting Current and very low ending current....just how does the voltage get up to 4v?

In test 4 you go from 3.30v only to 3.45v using 66ah. 

Is the point being made that really "zero" capacity is added after the cells reach 3.5v or so (reguardless of whether the charging voltage is even up to 4v)? And all the current capacity is stored under 3.5V. ?? (So then why charge or force the resting voltage over 3.5v?) (and if you charge at .5c your resting voltage will still come down to 3.5v or so, even though you may be stressing the cells to 4.15v by doing a .5c for a short time or a .1c for a long charge time?)


thanks for your time

Francis


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## GizmoEV (Nov 28, 2009)

spdas said:


> I will read through this a couple more times, but one thing strikes me in Test 3. How can you raise the voltage from 3.39 to 4v by adding only .6588ah into a 100ah cell? I see starting Current and very low ending current....just how does the voltage get up to 4v?


Very slowly... I've attached a graph of the data to help you see what is going on. The 0.6588Ah is the area under the red curve. In fact note the tiny area under the last two data points at 55 minutes and 85 minutes. Compare this to the fact that the majority of the Ah, 0.5537Ah in fact, were put in during the first 14 minutes of charge and the rest during the remaining 71 minutes!



> In test 4 you go from 3.30v only to 3.45v using 66ah.


That is right. It shows how much energy is stored between those two voltages in this 100Ah cell.



> Is the point being made that really "zero" capacity is added after the cells reach 3.5v or so (reguardless of whether the charging voltage is even up to 4v)? And all the current capacity is stored under 3.5V. ?? (So then why charge or force the resting voltage over 3.5v?) (and if you charge at .5c your resting voltage will still come down to 3.5v or so, even though you may be stressing the cells to 4.15v by doing a .5c for a short time or a .1c for a long charge time?)


That is exactly right!


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## Guest (Jan 21, 2011)

The resting voltages for the Hi-Power 100ah cells I have are around 3.3 volts. I charged to 3.7 and when we reached that point we stopped the charge. Within 10 minutes the resting voltage was 3.3 to 3.31 volts. Still after a week resting the resting voltages are holding steady at 3.3 volt for all 4 cells. The last time I charged I charged to 3.8 volts and they still rest at 3.3. I discharged them down to 2 volts and when we stop the run they bounce back up to about 3.1 volts. However there is no real charge left in them at that point. It is important to do AH counting in and out to help determine SOC. However if your running you can see that the voltages are down and that can give you a good indication of SOC while moving. So both voltage and AH in and out are important. If I was unaware and someone said they are flat at 2 volts and I get into a resting vehicle and the pack says 3.1 volts resting after a long drive I could be fooled into believing I still have a bunch of power left when I don't. Now my lead batteries would bounce back up too but no nearly that much and it would be easy to see I was low on power with just a volt meter. 

So no need to really charge higher than 3.6 volts per cell. Not much capacity above that point and if you do that little capacity will burn off real fast. 


Here are my charge numbers. 

3.17	3.16	3.17	3.19
3.26	3.25	3.26	3.26
3.26	3.26	3.26	3.26
3.28	3.27	3.27	3.28
3.3	3.29	3.3	3.3
3.33	3.33	3.33	3.33
3.34	3.34	3.34	3.34
3.34	3.34	3.34	3.34
3.36	3.37	3.36	3.37
3.38	3.39	3.38	3.39
3.39	3.41	3.38	3.41
3.43	3.46	3.42	3.45
3.45	3.48	3.43	3.48
3.5	3.55	3.5	3.54
3.55	3.57	3.52	3.58
3.62	3.63	3.6	3.64
3.67	3.67	3.66	3.69
3.72	3.71	3.7	3.72
Below is after stopping and resting for 10 minutes. These batteries are full. 
3.3	3.3	3.3	3.31


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## GizmoEV (Nov 28, 2009)

Francis,

Here is the graph of test 4. In it you can see several things. Initially I had a max voltage set on my PS and soon after the current started cutting back. This is because the PS was measuring the voltage at its terminals and not at the battery terminals. You can see that at 80min I cranked the voltage knob up on the PS so it again started putting out max current of around 3.5A.

At 300 minutes I decided that things were taking too long and this is where I paralleled the two power supplies in my unit which doubled the current.

At 665 minutes the current starts to drop again. From my data it looks like I had the voltage limit at about 3.425V. At 720 min there is a voltage drop where I went back to one PS. The voltage jumped again and then the current started to drop as the voltage stayed steady.

At 785 min I decided to make 3.45V my ending voltage so I cranked up the current again. The voltage then went over my target so I turned down the current so that the ending voltage was 3.450V.

The main reason I decided to post this graph is that you can see where the terminal voltage of this 100Ah cell would jump when the current changed. This shows why under charge or discharge the voltage is a poor indicator of SOC alone. It is important to have an Ah counter too, as gottdi pointed out. However, under low currents, getting the voltage to the beginning of the knee of the charge curve is ample to charge the battery 99% or more.


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## GizmoEV (Nov 28, 2009)

gottdi, Do you remember what your ending current was on that Hi-Power test?


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## Guest (Jan 22, 2011)

It was about 10amps. The manual charger I have does not have the ability to do a true CC CV so I started the charge with 15 amps and held it there as best I could since I can control manually the amps in. Once it got to like 3.6 I let the amperage start to drop both naturally and some intervention by me. Once I got to like 3.7 something I ended the charge. I have an Elcon but it's not set up for 4 cells so I did not use that. It's not going to be used until I have my bus ready. Gonna use the QuickCharger for the MG. I am going to send it in for a lithium algorithm. They will upgrade for a small fee. They just need to know the AH of the pack and how many cells and what cut off I want. 

Pete 

For testing it's my manual charger I must use. I can't control the voltage but I can control the amps to a degree. It will do up to 20 amps.


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## Overlander23 (Jun 15, 2009)

So what's the difference in resting voltage (after a night) between a cell charged to 3.6v and one that was charged to 3.6v but has been drained of, oh say, 20% capacity?


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## JRP3 (Mar 7, 2008)

I see a lot of concern with getting every last ah of capacity into a cell, yet Tesla and others undercharge their packs to increase cycle life. I'd say a 5-10% undercharge is desirable, unless your pack is so small that you will regularly take it to 90% DOD when driving by doing so. I'm considering skipping the CV phase and just shutting off the charger after the CC phase hits 3.45V or so, which should leave about 10% unused capacity when charging at 20 amps. Remember voltage changes with current, so shutting off the charger at 3.45V and 20 amps means a lower SOC than shutting off at 3.45V and 10 amps.


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## Guest (Jan 22, 2011)

Overlander23 said:


> So what's the difference in resting voltage (after a night) between a cell charged to 3.6v and one that was charged to 3.6v but has been drained of, oh say, 20% capacity?


Well if you jet off as soon as you pull off the charger then you still have a surface charge that will just disappear in an instant and your cells will drop like a rock to the resting voltage stage. I saw that in my 4 cell test. The batteries were at a very high resting voltage because of a previous overcharge. The moment I put a load on the cells dropped in voltage and within a minute the voltage was at 3.3. My cell resting voltage is 3.3. I can charge up and see maybe like 3.6 then jet off and that surface charge will just be gone. It is noticed on my lead pack too. So there is no need to cram in all that extra for a minute extra of power. It is not worth the life of the cell to do that. With the Hi-Power cells I think I can discharge them a bit extra than the TS or Calb but I dont charge quite as high either. But in the end it's a wash anyway. They all are about the same. Find the knee and stay put both top and bottom for your cells and run with that zone. If you need an extra battery or two then plug them in.


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## Guest (Jan 22, 2011)

JRP3 said:


> I see a lot of concern with getting every last ah of capacity into a cell, yet Tesla and others undercharge their packs to increase cycle life. I'd say a 5-10% undercharge is desirable, unless your pack is so small that you will regularly take it to 90% DOD when driving by doing so. I'm considering skipping the CV phase and just shutting off the charger after the CC phase hits 3.45V or so, which should leave about 10% unused capacity when charging at 20 amps. Remember voltage changes with current, so shutting off the charger at 3.45V and 20 amps means a lower SOC than shutting off at 3.45V and 10 amps.


I'd still do the CV stage. I think what it does is help balance the pack at that point. The cells that are a tiny bit lower will have a chance to catchup and those that are a tiny bit higher can't go higher. They just hang out with the gang so to speak. That CV stage I don't think is very long anyway. I think this is why many report having a well balanced pack after some time rather than a pack of imbalanced. cells. 

My CV state is terminated at 2amps. 

Pete


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## JRP3 (Mar 7, 2008)

Since all cells are getting the same amount of current how can some "catch up" to others?


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## GizmoEV (Nov 28, 2009)

JRP3 said:


> Since all cells are getting the same amount of current how can some "catch up" to others?


I've wondered about this. Does the internal resistance go up at higher voltages? If it does than maybe there can be some catch up of the lower cells. But it seems that if there is a higher resistance at higher voltages that more heat would be generated which would lower the resistance. I know JR has said the cells appear to get closer together over time. Maybe what he is seeing is due to something else.

JRP3, have you seen any converging of your cells? IIRC, you don't use any CManS (cell level management system) right?


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## JRP3 (Mar 7, 2008)

I have not seen any noticeable convergence as yet. I'm not sure what the convergence would be in reality. They won't change in capacity in relation to each other, they may have a tendency to somewhat top balance over time, though I'm not sure what the mechanism would be, but that just means they are more unbalanced at the bottom, so convergence may be the wrong term, if it exists at all. I am CMS free.


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## Guest (Jan 22, 2011)

At CV it holds the pack voltage and not cell voltage. So if any cells are out by a tad then they have the chance while the Constant Pack Voltage is being held while the amperage goes down as the cells do their last bit of filling. 

Pete


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## EVfun (Mar 14, 2010)

JRP3 said:


> Since all cells are getting the same amount of current how can some "catch up" to others?


I'm not sure if this is actually happening or not, but if the pack shows some convergence it would most likely be because charge efficiency is lower as the cell voltage rises above 3.4 or 3.5 volts. So when you hold the constant voltage at about that pack level the cells that are creeping ahead in voltage are charging less efficiently. That is, some small percentage of the amp hours (amp minutes at this point?) are being wasted as heat instead of moving Lithium ions.


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## JRP3 (Mar 7, 2008)

Yes that sounds plausible, and points toward top balancing as opposed to convergence. If you are running bottom balanced without a BMS then that would not be a good thing.


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## GizmoEV (Nov 28, 2009)

I've been trying to decide whether to bottom balance my pack this summer. It was top balanced last on July 28, 2010. It doesn't show signs of changing much, if at all. I still have my CManS boards in place but the top balance voltage on these is 4.00V and I'm not going over 3.5vpc so that feature is essentially unused. Maybe if I bottom balance and then continue to periodically monitor the voltage at end of charge I'll see if there is a top balancing trend. I agree, the term convergence is not the right term.


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## ElectriCar (Jun 15, 2008)

GizmoEV said:


> I've been trying to decide whether to bottom balance my pack this summer. It was top balanced last on July 28, 2010. It doesn't show signs of changing much, if at all. I still have my CManS boards in place but the top balance voltage on these is 4.00V and I'm not going over 3.5vpc so that feature is essentially unused. Maybe if I bottom balance and then continue to periodically monitor the voltage at end of charge I'll see if there is a top balancing trend. I agree, the term convergence is not the right term.


With this possibility of cells self balancing at the end of charge, a bottom balance would be negated over a few recharges. Whether to bottom balance or not should be based on whether you're going to charge it to that level or not if that is indeed happening. If you're going to stop at a safe level below the top thus not reaching that point, you should be fine bottom balancing. 

Based on what I understand about these things, I'm going to bottom balance. Otherwise if you do push the pack to get that last mile home so you don't have to call the tow truck, you have a much less risk of toasting a cell. You all know at times there's a diversion to your planned trip making it longer than expected. However so far in 7500 miles of driving I've only been stranded once, right after I got it on the road and didn't understand that lead batteries don't do near as well when really cold as they do when warm! Even then I just sat a few minutes and drove it another quarter mile or so then had to stop and repeat until I made it to a place to plug in my bad boy charger.


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## Guest (Jan 23, 2011)

I find the balancing on both ends if you don't go to far either way. So I can charge to 3.7 volts and my resting voltage will settle in at about 3.3. At the end it will settle in at 3.1 even if I go all the way to 2.4 while running. The amount that they are off while running is truly minimal. So if your batteries are out of whack like some of mine were then hook up your cells and discharge them then until the first one reaches like 2.2 volts. Let them sit for an hour or so then bring up the lowest of the cells by charging them until the match as close as you can. Do that cycle a few times and you will see how quickly they come together and it will be sort of bottom balancing. The goal is to get them as close as you can to begin with. Most new cells in a batch are not very far out if at all. Those do not need any intervention. Mine are slightly used and on pack to the other I have a few that were out of whack. I will be working on my MG pack this coming week. I have the pack together and I will go run the car out front up and down the road to discharge the pack. It will allow me to see what kind of mileage I get too. I will then bring up the low cells to match the others. It won't take long. 

Pete


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## GizmoEV (Nov 28, 2009)

ElectriCar said:


> With this possibility of cells self balancing at the end of charge, a bottom balance would be negated over a few recharges. Whether to bottom balance or not should be based on whether you're going to charge it to that level or not if that is indeed happening. If you're going to stop at a safe level below the top thus not reaching that point, you should be fine bottom balancing.


So far I'm not seeing a trend of the highest cell dropping in voltage at end of charge or the lowest cell comming up at end of charge. It could be because I'm only charging to 3.485vpc average. I'll have to collect more data to see what is going on.


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## spdas (Nov 28, 2009)

Aloha, although i am at the Kindergarden stage of understanding batteries, I have shown myself some very interesting things. I got a CBA 3 and played around with an AGM 9ah battery. Testing at 10amp draw, battery takes only 13mins to reach 10.5V. At 5amp draw i get 48 min. Now at 2.5 amp draw I project (gotta leave so estimating) 150 min. And this seems to be at predictable rates when you compare the immediate voltage sag when you start the test. So I think i will be able to judge my used Lifepo4 cells when they arrive this tuesday by viewing the sag. (BTW is this the Peukert thing)?

Francis


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## GizmoEV (Nov 28, 2009)

Yes that is the Peukert thing you are seeing. For LiFePO4 it is nearly non-existent so any Ah counter which has a setting for the Peukert exponent is usually set to 1. The CycleAnalyst I'm using doesn't have a setting for this and it seems to track reasonably well comparing discharge Ah and charge Ah. Note too that the temperature of the batteries has a big effect on the amount of voltage sag for a given current. Assuming you are not living on the top of the mountain you probably won't have to worry much about cold temps, however.


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## spdas (Nov 28, 2009)

I experimented and got very diminishing and surprising AH results as I went from------ 

.25C (140min and total 6AH) 
and at 
.50C (48min and total 4AH) 
and at 
1C (13min and total 2.25AH) 
on the AGM non deep cycle 9ah battery. To go from 13v to 10.5v
and get the number of amps back at that C rating.

Then to me then it seems a better idea to buy a larger Lifepo4 pack than you could get away with and use them at a lower C rating and get a lot more miles out of the pack. But now you have to contend with extra weight and extra $ for batteries! In other words Available Amps v.s Miles is not linear when using different C's.

Francis


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## GizmoEV (Nov 28, 2009)

That is correct and definitely so with lead-acid batteries. If you drain that 9Ah battery at the 20 hour rate, I believe it is labeled as C/20, or 0.45A you will likely get 9Ah out of the battery. That is why an EV never plans on using the full battery Ah rating in addition to the fact that greater than 50% DOD starts to significantly shorten the life of the battery.

Remember, however, that for LiFePO4 that your results would have been entirely different even with a 9Ah battery. TS shows getting full capacity at 1C. The internal resistance of a LiFePO4 battery is so low that most of us ignore it in our Ah counting since we don't plan on using more than 70-80% of the capacity any way.

Basically if you built two identical EVs except one with lead acid and one with LiFePO4 say with 100Ah packs using the C/20 rate figure on only getting ~50Ah out of the lead acid pack to not go to far below 50% SOC but you could safely get a full 70Ah out of the LiFePO4 pack and only dip slightly below 70% DOD under high currents. It truly is amazing.


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## GizmoEV (Nov 28, 2009)

I finally got my CycleAnalyst data port hooked up to my laptop and I recorded a charge from a short drive which used about 11.5Ah from my 200Ah pack. You can see the voltage take a quick jump as the charger started up. The highest pack voltage reading was 69.78V. The jumpiness of the current reading I believe is due to the sampling rate of the CA and the pulsing charge of the Zivan. I don't have a scope to watch the wave form of the charger but I've heard of one other person asking me if I saw the same behavior. I guess that would be a yes. The Ah in seems to track reasonably close to the Ah out so I guess the meter is tracking reasonably well. At the end of charge you can see the voltage drop slightly. This is during the time the charger is in the last phase and it just comes on for brief moments at a few mA. Since I have a 500A shunt the charge current reading only has a 0.1A resolution. The data is at a 30 second sampling rate.

The current started ramping down at about 69V at the 43min mark and was below 500mA at the 58min mark. At best only 0.03Ah were added after that point. In fact, only about 0.75Ah were added after the 43minute mark where the current just dropped below 11A or 0.055C. It looks like it doesn't matter much in the capacity department if you let your charger ramp all the way down to minuscule currents. This is with a 3.485vpc cut off voltage.


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## spdas (Nov 28, 2009)

Now I can't wait for my Lifepo4 to arrive in a couple of days so I can test them!. But for the Lead, I can safely say that if i had 100ah batteries and got 50 miles out of them per charge, I am sure if i had 200ah lead batteries instead I would get 115-125 miles out of them per charge.

(now I am testing 10amp draw on the 9ah SLA's to 10.5v. I will let them rest for 15 minutes and then see how many more amps I can coax out at .05ah draw) vs .05 ah draw from the start.) 

Francis


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## ElectriCar (Jun 15, 2008)

Francis I have 232ah flooded lead batteries, 24 for a 144V pack, 4147lb truck and get about 30 miles/charge in the summer. Winter I may get 15 with normal driving, 20 or so if I baby it. The key of course is to have the batteries at a temperature of around 60F or so. And I can't wait until my 50 200ah Calb cells arrives in about a month!


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## GizmoEV (Nov 28, 2009)

My pack is essentially 20 cells at 200Ah. Nominal voltage is close to 3.2vpc so 64V. This gives me a 12.8kWh pack. I can go a comfortable 70 miles in warm weather and not go below 80% DOD. ElectriCar's new pack is 32kWh which is 2.5 times the energy of mine. I expect he will get a similar range in his pickup as I do in my Gizmo, possibly more if driven gently.

What ever you do, make sure you have an Ah counter installed so you have a good idea where you are on the discharge path.


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## ElectriCar (Jun 15, 2008)

I ordered the in-dash Cycle Analyst Friday. They are discontinuing that model and only selling it in an enclosure now. But I think it's a great device with lots of data. It has a low voltage feature. Any idea how it can be made to shut down or limit the throttle?


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## Guest (Jan 24, 2011)

> Any idea how it can be made to shut down or limit the throttle?


Did you ask the guys who make it? 

Pete


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> I ordered the in-dash Cycle Analyst Friday. They are discontinuing that model and only selling it in an enclosure now. But I think it's a great device with lots of data. It has a low voltage feature. Any idea how it can be made to shut down or limit the throttle?


http://www.ebikes.ca/drainbrain/CycleAnalyst_Manual_Vers223.pdf

7. Using the Limiting Features
There are many situations when it is desirable to limit the amount of
power that the controller is able to draw from the battery pack. For
instance, you might want a current limit in order to:
A) Protect the cells in a battery pack from delivering more than their
rated amperage
B) Extend the range of your vehicle by reducing current draw during
acceleration and hill climbing
C) Safely cycle at low current a NiMH or NiCad pack that has been
sitting unused for a long period
D) Keep the motor's power within a legally stipulated power limit
A speed limit can help make any electric bicycle abide by the legal
speed caps that exist in most jurisdictions while not affecting
performance below that speed. It can also be useful for extending the
range or for taming a setup that is otherwise too fast for comfort,
without sacrificing hill climbing torque.
The voltage limit is used primarily to prevent the battery pack from
being over discharged which can be damaging to the cells. Typically,
you would set it between 29 to 31V for a 36V pack, and between 39 to
41V for a 48V pack.
7.1 How the feedback works
To understand how the limiting features work, just imagine how you
would operate the throttle manually. If you are going over a desired
speed limit, you would back off the throttle. If the vehicle then reached
a hill and started to slow down from your target speed, you would
further engage the throttle, thus continuously adjusting the throttle
position to keep at your desired velocity.
38.4 V 25.6 kph
3.13 A 6.214 Ah
Select
Watts
or
Amps
12
The Cycle Analyst behaves similarly. When it senses that any one of
the limiting quantities has been exceeded, then the throttle over-ride
signal starts to decrease from its default resting value (usually
between 4 to 5V, determined by ITermMax). A simple circuit is required
so that the controller only sees the lower value of the throttle signal or
the Cycle Analyst signal. This is generally achieved with a diode as
follows:
There are various setup options which control the speed at which the
Cycle Analyst responds to these signals. If the settings are too fast,
then the control can be twitchy or oscillate around the desired value,
while gain settings that are too low will cause a long lag time before the
limiting kicks in.
7.2 PI Controller
Each of the three limiting features is implemented as a digital
Proportional/Integral (PI) controller. The actual output for speed
regulation is computed as follows:
ITerm = Previous ITerm + IntSGain*(Set Speed - Actual Speed)
Clamp: ITermMin < ITerm < ITermMax
Override = ITerm + PSGain*(Set Speed - Actual Speed)
Similar values are calculated with the current limit, and low voltage
limit, and the smallest of the three over-ride terms is output as a
voltage. If this output is less than the user’s throttle voltage, then it is
the Cycle Analyst which is ultimately controlling the vehicle.
7.3 Tuning


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