# Constant Voltage charging for LA, pro and con?



## Sunking (Aug 10, 2009)

Stunt Driver said:


> Why Constant Voltage charging is not considered like an option for DIY conversion?


Who said it is not an option? It just takes longer, and possible no option for an equalization charge.

The one thing I will say if you are going to use constant voltage method you need to make sure of two things to be effective.

The voltage is precisely controlled and adjustable to match the battery chemistry it is being applied to. 
That the current is between C/8 to C/10 range, otherwise it can take forever but if kept in this range batteries will be fully charged in 24 hour maximum.

The only problem you might run into is if the charger does not have an equalize charge. This is needed from time to time to equalize battery cell voltages and prevent sulfate buildup issues.

As for me, I use a quality 4-stage algorithm.


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## Stunt Driver (May 14, 2009)

In my case - each battery will be on it's own 14.4 power supply, and no equalization needed here. 
That is another nice thing about this setup - S I M P L E.

And 8 A seems to be a good charge for 125AH MAXX. Let's say batt is 50% DOD, then 65AH devided by 8A is only 8 hours if current stays flat, which won't happen ofcourse, but I usually stay home for more than 10 hours, and batteries are normally not 50% dod


PS Sunking - how long does you "quality 4-stage algorithm" take to fully charge battery? I bet at the same current - yours and mine will reach 80% SOC within the same time!


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## ga2500ev (Apr 20, 2008)

Stunt Driver said:


> In my case - each battery will be on it's own 14.4 power supply, and no equalization needed here.
> That is another nice thing about this setup - S I M P L E.


It is simple But it seems to me that you can gain a bit of an advantage in a 2 stage system without too much additional effort with the addition of a relay per charger. The purpose of the relay is to switch in/out the dropping diodes (which you're going to need anyway). Wire all the relays to a cheap timer and power supply (which could easily be another laptop charger).

This is how it would work, At the beginning of the charge cycle you set the timer to turn the relays on, which drops out the diodes. So the full full charger voltage is available to the battery. Since it's only 8 amps, which is C/16, you don't even need to worry about current limiting.

When the timer times out, the relays turn off which switches in the diodes and lowers the voltage to the batteries.

The nice thing about it is that since you have 16V available you can do an equalization charge when needed by simply setting the timer and charging the batteries when they are already fully charged.

A good relay may be this 12V 40A automotive relay from All Electronics:

http://www.allelectronics.com/make-a-store/item/RLY-540/12-VDC-SPDT-40-A-RELAY/1.html

At $1.35 each (and another $3 for dual automotive sockets) it won't break the bank to implement.



> And 8 A seems to be a good charge for 125AH MAXX. Let's say batt is 50% DOD, then 65AH devided by 8A is only 8 hours if current stays flat, which won't happen ofcourse, but I usually stay home for more than 10 hours, and batteries are normally not 50% dod


It's a little light. But OTOH charging with free supplies cannot be beat.



> PS Sunking - how long does you "quality 4-stage algorithm" take to fully charge battery? I bet at the same current - yours and mine will reach 80% SOC within the same time!


Doubtful. Bulk charging allows for the input voltage to rise above 14.4V as long as the current is limited. Since the voltage is higher, more energy is being put into the battery in the same time frame. So it by definition must charge faster.

I find Lee Hart's charging basics page to be the most clear discussion on the net:

http://www.evdl.org/pages/hartcharge.html

ga2500ev


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## Stunt Driver (May 14, 2009)

ga2500ev said:


> Since the voltage is higher, more energy is being put into the battery in the same time frame. So it by definition must charge faster.


Have to disagree with this.

If at given current you have higher voltage on battery lugs - battery dissipates more energy, but not nesessarily absorbes more energy. Look into why would voltage go up on discharged battery? Junk batteries will have voltage Jump up, but guess how much energy is being put into them?

to get 100AH battery from 0 to 100% you have to put 10A thru it for 10H. It doesn't matter what voltage battery goes up to during charge. IMHO ofcourse


And besides, the only advantage you show - faster charging? Which I agree to give up - I leave car charging overnight, and do not care was it finished by 3Am, 6AM or 8 AM when I have to drive it out


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## dtbaker (Jan 5, 2008)

My understanding is that FLA need at least occasional over-voltage to get them to gas and reduce Sulphation on the plates.


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## Stunt Driver (May 14, 2009)

100% agree threre. Occasionally i'll throw my Shumacher's clamps on battery and let it go thru proper charge overnight. But probalby once a month, not more.
At this moment I am afraid that daily desulfation at higher voltages actually kills batteries


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## dtbaker (Jan 5, 2008)

Stunt Driver said:


> 100% agree threre. Occasionally i'll throw my Shumacher's clamps on battery and let it go thru proper charge overnight. But probalby once a month, not more.
> At this moment I am afraid that daily desulfation at higher voltages actually kills batteries


If you already HAVE a full cycle 2-stage charger, why not use it?

I seriously doubt the equalization charge phase kills batteries as ALL the industry standard FLA batteries do it. As long as you keep your batteries WATERED properly!


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## Stunt Driver (May 14, 2009)

well, if you dig bit in archive, there was a interesting post on solar bank usage. Batteries live much-much longer if they don't see voltage above 14.5 volts, maybe only except rare equalization.


I have 4 chargers, but all my reasons not to use them are above the thread. Shortly - too much interaction required, and they take valuable accessible space. Want not to even open hood - just plug in and go. Plus I am expanding my pack from 48 to 84 volts, and don't want to invest more $$ in charging. Schumachers were great for start up - reliable, show voltage, easy to snap on any battery. Now that I know what to expect from batteries, and I'm installing individual voltage monitor on dash - I want to simplify charging end. Also, I can possibly sell chargers.


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## ga2500ev (Apr 20, 2008)

Stunt Driver said:


> Have to disagree with this.
> 
> If at given current you have higher voltage on battery lugs - battery dissipates more energy, but not nesessarily absorbes more energy. Look into why would voltage go up on discharged battery? Junk batteries will have voltage Jump up, but guess how much energy is being put into them?


To quote the Hart battery charging page:



> The most basic rule is that you can charge at any current you like until the battery reaches 2.4 volts per cell at 25 deg. C (77 deg. F). That's the familiar 7.2v per 6v battery, or 14.4v for a 12v battery. Below this voltage, essentially *100%* of the current goes into charging the battery, so there is negligible heating or gassing.




So I reiterate that when batteries are discharged and the terminal voltage is below 14.4V that all of the energy, regardless of either voltage or current, will go into charging the battery.




> to get 100AH battery from 0 to 100% you have to put 10A thru it for 10H. It doesn't matter what voltage battery goes up to during charge.


Of course it does. You charge batteries with energy. Energy is measured in watts which is voltage x current. If the voltage is higher at the same current, then more energy is being put into the battery over the same time period. So by definition the time period to fill the battery with a specific amount of energy will be shorter if more energy is available.

BTW I wasn't talking about the battery voltage, I was talking about the input voltage of the charger.



> IMHO ofcourse
> 
> 
> And besides, the only advantage you show - faster charging? Which I agree to give up - I leave car charging overnight, and do not care was it finished by 3Am, 6AM or 8 AM when I have to drive it out


The other advantage is that you have a system that can equalize the batteries, which will prolong the life of your batteries and prevent premature death.

BTW when you drop 8A @ 2V across the diodes, you burn that 16W x your number of batteries up as heat. So another advantage is that you are actually putting wall power into the battery instead of just burning it up as heat. You charge batteries every day. This will represent a cost savings.

It's a single relay per battery and a small bit of wiring. But it'll give you quite a few advantages over simply doing CV charging.

ga2500ev


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## Sunking (Aug 10, 2009)

Stunt Driver said:


> In my case - each battery will be on it's own 14.4 power supply, and no equalization needed here.
> That is another nice thing about this setup - S I M P L E.


Hold up there, 14.4 is not a float voltage for a 6 cell FLA battery, let's talk 13.2 to 13.5 depending on which lead type we are talking about. 



Stunt Driver said:


> And 8 A seems to be a good charge for 125AH MAXX. Let's say batt is 50% DOD, then 65AH devided by 8A is only 8 hours if current stays flat, which won't happen ofcourse, but I usually stay home for more than 10 hours, and batteries are normally not 50% dod


A little low IMHO for a float charge. It will work just take longer. For a 125 AH 12 to 16 amps is the sweat spot for a C/10 to C/8 range.




Stunt Driver said:


> PS Sunking - how long does you "quality 4-stage algorithm" take to fully charge battery? I bet at the same current - yours and mine will reach 80% SOC within the same time!


Not too long depending on DOD 3 to 8 hours.


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## ga2500ev (Apr 20, 2008)

Sunking said:


> Hold up there, 14.4 is not a float voltage for a 6 cell FLA battery, let's talk 13.2 to 13.5 depending on which lead type we are talking about.


Sunking, he's not talking about a float charge. Stunt Driver wants to skip the bulk charge and only use the contant voltage absorption charging phase. These type of chargers are often called taper chargers.



> A little low IMHO for a float charge. It will work just take longer. For a 125 AH 12 to 16 amps is the sweat spot for a C/10 to C/8 range.


Yup. But when the charger in question (A laptop charger) is essentially free, I can see why he's willing to live with a bit of a current limit.

But that's the reason I argued that a bulk charge phase is even better here. Putting 16V @ 8A in at the bulk phase gives nearly the equivalent of 0.8A more current than if the voltage were set at 14.4V.

ga2500ev


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## Sunking (Aug 10, 2009)

Stunt Driver I am not sure but I don’t think we are on the same page with reference to 2, 3, and 4 stage charging algorithm, or float chargers. It can be a bit confusing.

I will define my version of a 3-stage algorithm. Stage 1 is the BULK charge at a set constant current of C/10 to C/8 up to a set voltage of 2.3 to 2.45 volts per cell. At that point it switches to ABSORPTION charge, well actually no switch occurs the charger then goes into constant voltage mode of the set voltage of 2.3 to 2.45 volts per cell and keeps this voltage fixed until the current tapers off to 1 to 3 % of the initial charge rate. Then at that point it switches to FLOAT mode where the voltage is reduced to around 2.2 to 2.25 volts per cell and remains there until you suspend the charge. The float mode just keeps the battery fully charged and overcomes the self discharge.

Now with that said you can just use a float charger of 2.2 to 2.25 volts per cell, but the charger needs to at least provide a decent charge rate. Again I go back to C/10 to C/8. This works real good for batteries in emergency standby service like telephone companies and UPS systems. The down side is it takes longer and not a good algorithm for deep cycle service like that used in EV’s where the batteries are constantly charged and discharged cycled. Using a float type charger in deep cycle service allows sulfate build up.


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## Sunking (Aug 10, 2009)

ga2500ev said:


> Sunking, he's not talking about a float charge. Stunt Driver wants to skip the bulk charge and only use the contant voltage absorption charging phase. These type of chargers are often called taper chargers.
> 
> But that's the reason I argued that a bulk charge phase is even better here. Putting 16V @ 8A in at the bulk phase gives nearly the equivalent of 0.8A more current than if the voltage were set at 14.4V.
> 
> ga2500ev


Ok I understand what you are saying, but there is a slight problem. Let's say you use a charger rated at say 15 volts @ 8 amps OK?

Now connect that to say a 100 AH battery that is say 50% DOD. There is no way a 8 amp charger can supply that battery with 15 volts. The voltage will fold back to say 12 volts and go into constant current mode of 8 amps. Whick is the BULK stage. Then once the battery gets fairly well charged up the voltage will rise up to 15 volts and at that point the charger goes into constant voltage and the current tapers off or the ABSORPTION charge. Which is basically a 2-Stage charger. The danger is leaving at 15 volts on for too long after the current drops below 3% of the. As long as you can monitor you are OK. If something happens and you have to leave, you can do some serious damage. Hence the 3rd automatic stage of cutting the voltage back to a safe FLOAT voltage.

I think we might be talking about some of the same stuff, just different views of when and how much.


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## Stunt Driver (May 14, 2009)

Sunking said:


> Hold up there, 14.4 is not a float voltage for a 6 cell FLA battery, let's talk 13.2 to 13.5 depending on which lead type we are talking about.


Who talks about float? 14.4 is a normal voltage in any ICE car, or boat, to charge starting, and most of deep cycle batteries. My batteries are dual purpose, why wouldn't they be happy with 14.4 to charge?
As for 16A charge - i think it's reasonable, i'll just parallel another set of PSUs. However, I believe in slow charge as being a lot better for batteries 



Sunking said:


> Not too long depending on DOD 3 to 8 hours.


then it's just like mine


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## ga2500ev (Apr 20, 2008)

Sunking said:


> Ok I understand what you are saying, but there is a slight problem. Let's say you use a charger rated at say 15 volts @ 8 amps OK?


Sure.



> Now connect that to say a 100 AH battery that is say 50% DOD. There is no way a 8 amp charger can supply that battery with 15 volts. The voltage will fold back to say 12 volts and go into constant current mode of 8 amps. Whick is the BULK stage.


Correct.



> Then once the battery gets fairly well charged up


The bulk stage works until the battery gets to about 80% SOC. At that point the terminal voltage should be 14.4V.



> the voltage will rise up to 15 volts and at that point the charger goes into constant voltage and the current tapers off or the ABSORPTION charge. Which is basically a 2-Stage charger.


I'm with you all except for the 15V. My understanding is that once you reach 14.4V you need to limit the charger voltage to 14.4V or the battery will start gassing.



> The danger is leaving at 15 volts on for too long after the current drops below 3% of the. As long as you can monitor you are OK. If something happens and you have to leave, you can do some serious damage. Hence the 3rd automatic stage of cutting the voltage back to a safe FLOAT voltage.


Correct. And I've seen current cut offs in the range of 1% to 3% of the Amp Hour rating of the battery. So in this case once the charging current drops to under 2A, then the battery is at 100% SOC and you should cut the charger off or drop the voltage to a float voltage of 13.8V.



> I think we might be talking about some of the same stuff, just different views of when and how much.


Nope. Same stages. Same names. Same types. Only discrepancy is the terminal voltage at the end of the bulk stage.

ga2500ev


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## Stunt Driver (May 14, 2009)

First test of my CV charger went well. MAXX 29 battery charged with CV holds voltage under load just a bit better than other 3, charged by Schumacher Smart-Chargers. 

I'll keep looking, but so far doesn't seem like a bad idea!



By the way, I have also tried relay approach (to let voltage go up to 15v, and then drop to float volatge) - but don't think it worths it: takes space, may fail, AND - doesn't seem to give any benefit, based on first test


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## ga2500ev (Apr 20, 2008)

Stunt Driver said:


> First test of my CV charger went well. MAXX 29 battery charged with CV holds voltage under load just a bit better than other 3, charged by Schumacher Smart-Chargers.
> 
> I'll keep looking, but so far doesn't seem like a bad idea!


Well that's good.




> By the way, I have also tried relay approach (to let voltage go up to 15v, and then drop to float volatge) - but don't think it worths it: takes space, may fail, AND - doesn't seem to give any benefit, based on first test


I saw your first crack at it. Seemed like it would oscillate because it wasn't latched. I think it was too complicated because it tried to use the terminal voltage to switch at the end of the charge cycle.

My idea OTOH was to use a timer at the beginning of the charge cycle to kick the relay in, then have it drop out after a fixed period of time bringing the diodes into the loop at a lower fixed voltage. No oscillation and less control circuitry.

As a backtop, I would suggest adding Lee Hart's zener shunt regulators to each battery too. With only 2 zener diodes and an auto light to bypass excess terminal voltage, it'll ensure that your batteries sill not sit and boil for any reason. You can find a detailed discussion and a construction PDF here:

http://teva2.com/projects.htm

I'm interested because I'm planning on going this route...

ga2500ev


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## peggus (Feb 18, 2008)

ga2500ev said:


> Of course it does. You charge batteries with energy. Energy is measured in watts which is voltage x current. If the voltage is higher at the same current, then more energy is being put into the battery over the same time period. So by definition the time period to fill the battery with a specific amount of energy will be shorter if more energy is available.
> 
> 
> BTW I wasn't talking about the battery voltage, I was talking about the input voltage of the charger.



This is not quite right. Batteries store charge, coulombs, Ah etc. Not really energy. Energy is a nice and useful side effect, but to say that a battery store energy is like saying that an air-tank with compressed air stores energy. You can get energy out of compressed air but the amount depends on a whole slew of external factors, the amount of air molecules you can get out of the tank is constant, or as much as you put in.

Batteries are the same way, the amount of charge you can get out is the same as the amount you put in. (ignoring equalization here) 

The problem with your above statement is that the battery dictates the voltage at the terminals not your charger. The higher voltage charger will charge the batteries faster because it stays in constant current mode longer hence resulting in a higher average current for the duration of the charge. 



ga2500ev said:


> The other advantage is that you have a system that can equalize the batteries, which will prolong the life of your batteries and prevent premature death.
> 
> BTW when you drop 8A @ 2V across the diodes, you burn that 16W x your number of batteries up as heat. So another advantage is that you are actually putting wall power into the battery instead of just burning it up as heat. You charge batteries every day. This will represent a cost savings.
> 
> ...



This I agree with!

Another solution is to tweak the voltage divider inside the power supply to fool it that it's outputting a different voltage than it actually is. Every switched mode power supply has a resistor divider on its output that is used to measure the voltage. I've found that you can tweak them over quite a range by changing this divider. In you application you could use a optocoupler to switch in a resistor in parallel with one side of the divider to raise the output voltage for the EQ phase.


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## yarross (Jan 7, 2009)

dtbaker said:


> I seriously doubt the equalization charge phase kills batteries as ALL the industry standard FLA batteries do it. As long as you keep your batteries WATERED properly!


Equalization does kill LAs, by oxidation of + plates grids. Unfortunately, not equalizing will kill them as well, because others factors will dominate.
LAs are a buch of painful compromises


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## Sunking (Aug 10, 2009)

ga2500ev said:


> The bulk stage works until the battery gets to about 80% SOC. At that point the terminal voltage should be 14.4V.
> 
> I'm with you all except for the 15V. My understanding is that once you reach 14.4V you need to limit the charger voltage to 14.4V or the battery will start gassing.


Not exactly accurate, you have to be vendor and chemistry specific.

Just using Trojan as an example they recommend 2.6 vpc for their FLA series which is 15.6 volts on a 12 volt configuration. A little gassin is a good thing as it keeps sulfation off the plates.


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## dtbaker (Jan 5, 2008)

this is the crux of my question.... is a 2.6vpc stage GOOD or BAD to do EVERY cycle? The off-grid solar guys who use deep cycles say the 2.4vpc charge is better for the life of the cells, and the 2.6vpc should only be done 'occasionally' to equalize. I have not seen any quantitative number like 'every x cycles.'

I believe it is the RATE of the bulk charge that helps prevent sulfation, not the voltage. The target rate being .3C, or whatever your charger can handle. At least, this is what I have been reading....


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## Sunking (Aug 10, 2009)

dtbaker said:


> this is the crux of my question.....


Ok I understand. I design/build quite a few off-grid solar systems. And again it comes down to 2 things.



 What manufacture and model number?
 Charge rate.
 
For my telephone company designs (remote cell tower sites) we use strictly Rolls Surrette RE series. Home brewers everything under the sun from junk to Trojan and Surrette. 

 The voltage you select is a compromise of trade-offs. On the lower end say 2.3 vpc the battery wants to be fully charged to get maximum capacity and avoid sulfation on the negative plate. At the other end say 2.6 vpc, a continually over-saturated condition, can cause grid corrosion on the positive plate. It also promotes gassing, which results in venting and loss of electrolyte. 

After 35 years of working with the manufactures here is my best suggestion. Choose the exact middle ground. For example using Trojan again. They suggest 2.45 to 2.7 vpc so 2.575 vpc is the sweat spot or 15.45 volts for a 12 volt stack using Trojan as an example. Look up your battery manufacture specs and see what the range is for your application.

FWIW, ignore the solar guys, they don't know too much and forget something very important. They do not have a sloar system that can use a true 3-stage charging algorithm. I kno wof no place on the face of the earth where you get a 10 to 12 Sun Hour day of insolation.


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## dtbaker (Jan 5, 2008)

I have a pack of 12 x8v US battery us8vgchcx 'golf cart' deep cycle floodies... definitely not junk batteries. ; 183aH 20-hr capacity. 

I also now have a Flow-Rite watering system installed which seems great in that the system requires less water as the caps seem to catch some, and watering to exact same level in all cells is automatic and EASY... It was a total pain by hand for the first 6 months, and if you've read earlier posts, I fear that I was hard on the cells by under-watering and probably not consistent cell to cell since some were hard to see and get to.

What I am trying to find out here is whether the default curve from Zivan for the ng-1 charger is the 'best' for battery life, or not. The initial phases are right in line w/ normal for FLA in that it does a CC, then CV to bring system to 2.4 vpc and senses when charge drops to about 2 amps. what happens NEXT is the question.

The Zivan then ups the target voltage to 121 (2.52 vpc) and holds at 2 amps until it gets there or times out before dropping to a trickle charge. As my batteries have aged, it no longer seems to 'get there', and I am questioning whether that last jolt is good or bad in the first place to do on a daily basis.


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## Sunking (Aug 10, 2009)

dtbaker said:


> I have a pack of 12 x8v US battery us8vgchcx 'golf cart' deep cycle floodies... definitely not junk batteries. ; 183aH 20-hr capacity.


I never meant to imply your batteries were junk. So if you took it that way I apologize. 

My other train of thought is run on the low end say 2.35 for example. Then monitor temp corrected spg and cell voltage and when you see an imbalance apply the high end voltage as to act as an equalization charge to bring the cells back in balance. 

As i am sure you know any lead acid battery just looses capacity over time with each cycle and is accumulative. Even the best cared for lead acid battery is pretty much shot in 3 to 5 years. Some studies suggest about 300 to 500 cycles is all you are going to get.

Good Luck


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## dtbaker (Jan 5, 2008)

Sunking said:


> I never meant to imply your batteries were junk. So if you took it that way I apologize.


not taking it personally. 



Sunking said:


> My other train of thought is run on the low end say 2.35 for example. Then monitor temp corrected spg and cell voltage and when you see an imbalance apply the high end voltage as to act as an equalization charge to bring the cells back in balance.


the high voltage set points are not tweakable by me.... factory set. best I can do is to unplug when CV phase ends. 



Sunking said:


> As i am sure you know any lead acid battery just looses capacity over time with each cycle and is accumulative. Even the best cared for lead acid battery is pretty much shot in 3 to 5 years. Some studies suggest about 300 to 500 cycles is all you are going to get.
> 
> Good Luck


yeah... although with 'proper care' and average 50% DOD I was hoping for closer to 700 cycles.... which is still only two years with daily use. So, with a rough first 6 months, a one year (300-ish cycle) life is probably not unheard of....


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## Stunt Driver (May 14, 2009)

ga2500ev said:


> I saw your first crack at it. Seemed like it would oscillate because it wasn't latched.


I have connected transistor output and relay NO contact - this works as self-latching link, so that one was solved. Still difficult to set exact cutoff voltage. And the only result that this seems to achieve - speed up charging process at expense of higher current at near full battery, which not necesserily is good.




ga2500ev said:


> My idea OTOH was to use a timer


Seem you can easily overcharge batts, if they aren't as empty as yout think. Such a complication - to figure out DOD and then needed time, and for the only reason of speeding up charge?? Well, I may be oversipmlifying my solution - but I like EASY and ROBUST constructions.




One more, about charging with high currents - I know people been saying it is good for batteries, but I don't believe. It is not proven!

Solar banks leave long time - because they NEVER get high-current charge, it's just not available from PV panels.

Also, not the same chemistry but same idea - my 12 year old NiCd batteries for camera are still good, because I use 16 hour charger for them. I have purchased set of newer batteries with 30 min charger - and batteries went junk after about a year. 
So I believe slower charge is good for battery. 
From common sence - battery has complicated chemical process going on, forced by charge current. Since it is based on surface, rather than in volume - I do not believe chemical layers will form properly if you push the speed of process up. IMHO but proven by personal experience


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## ga2500ev (Apr 20, 2008)

Stunt Driver said:


> I have connected transistor output and relay NO contact - this works as self-latching link, so that one was solved.


That's good.



> Still difficult to set exact cutoff voltage. And the only result that this seems to achieve - speed up charging process at expense of higher current at near full battery, which not necesserily is good.


Setting the cutoff could be done easier with a consistent voltage reference instead of just a voltage divider. Would add an opamp to the mix though.



> Seem you can easily overcharge batts, if they aren't as empty as yout think. Such a complication - to figure out DOD and then needed time, and for the only reason of speeding up charge?? Well, I may be oversipmlifying my solution - but I like EASY and ROBUST constructions.


That's why I suggested adding the shunt regulator. They simply would not allow the batteries terminal voltage to rise above a certain point because the excess energy is used to light the lamp.

There's a reason that high end chargers are pricey. I still believe that an 8 pin microcontroller and a bit of fluff can easily handle the issue on a per battery basis though.

ga2500ev




One more, about charging with high currents - I know people been saying it is good for batteries, but I don't believe. It is not proven!

Solar banks leave long time - because they NEVER get high-current charge, it's just not available from PV panels.

Also, not the same chemistry but same idea - my 12 year old NiCd batteries for camera are still good, because I use 16 hour charger for them. I have purchased set of newer batteries with 30 min charger - and batteries went junk after about a year. 
So I believe slower charge is good for battery. 
From common sence - battery has complicated chemical process going on, forced by charge current. Since it is based on surface, rather than in volume - I do not believe chemical layers will form properly if you push the speed of process up. IMHO but proven by personal experience[/quote]


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## Stunt Driver (May 14, 2009)

Yeah, a shunt, and a microcontroller sure will keep batteries happy, but gets overcomplicated. And again, what is your guess for benefit? I.e. what will you get in return, except slightly faster charging?? From what I see so far - battery charged with CV holds just as well (within .1v) as one charged with 3 stage smart charger




My take - it just doesn't worth it for a convertion with Lead-Acid batteries. Proove me wrong with numbers if you can.


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## ga2500ev (Apr 20, 2008)

Stunt Driver said:


> Yeah, a shunt, and a microcontroller sure will keep batteries happy, but gets overcomplicated. And again, what is your guess for benefit? I.e. what will you get in return, except slightly faster charging?? From what I see so far - battery charged with CV holds just as well (within .1v) as one charged with 3 stage smart charger


My argument really wasn't ever for faster charging. I just never saw the sense of wasting power into heat via the dropping diodes instead of just putting that power into the battery.

Other than the equalization issue, I don't believe anyone has said that CV charging wouldn't work. I believe that the only point that may have been missed is that it's possible to overcharge a LA battery even with a CV charger if you leave it on too long.

The only reason that I brought the microcontroller into the mix was that it can manage that multstage functionality (CC,CV,float) without a whole lot of external equiment per board. The minute you have to have a board per battery, the only complication becomes what goes on the board.



> My take - it just doesn't worth it for a convertion with Lead-Acid batteries. Proove me wrong with numbers if you can.


I really don't need to prove anything. You have a solution that works for you. I wasn't trying to talk you out of it. I was just pointing out the costs (wasted power, possible overcharging), and the alternatives (shunt regulator, multistage charging, temp compensation, etc.).

BTW the shunt regulator accomplishes both your and my goals with very little more complexity. Fundamentally using the zeners makes a diode that doesn't kick in until the threshold lever is reached. So early in the charge cycle, all the power goes into the batteries and non into the diodes and lamp. As the cycle progresses and the terminal voltage rises the circuit shunts more of the excess power away from the battery.

It's simple, rugged, and can be built into a permanently attached cable, one per battery.

ga2500ev


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## Stunt Driver (May 14, 2009)

Interesting about Zeners. Have a link handy explaining concept?
Because from my current understanding - zener, unlike my diodes, goes across the battery, and is supposed to pass ALL excess current thru itself, to keep voltage across battery within limits. In my case it would mean - up to 7A at 14V, which is a 100W per zener. That is what I call waste! Ofcourse it will only happen after battery is nearly fully charged, but how can you even dissipate that much???

While my oversimple thing dissipates only 16w (2v at up to 8A) and only while battery is charging. Once it reached 14v - current drops to ~1A, which is 2w of waste. To charge 50% DOD 125AH battery - i waste appr 130wh per battery. Which calculates to be much less than zener case.



That is why I asked for numbers. While diodes to drop voltage seem like a rood solution - it's not that bad numberwise. And doesn't require board.


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## ga2500ev (Apr 20, 2008)

Stunt Driver said:


> Interesting about Zeners. Have a link handy explaining concept?


Try this one:

http://www.electronics-tutorials.ws/diode/diode_7.html



> Because from my current understanding - zener, unlike my diodes, goes across the battery, and is supposed to pass ALL excess current thru itself, to keep voltage across battery within limits. In my case it would mean - up to 7A at 14V, which is a 100W per zener. That is what I call waste!


What you are missing is the fact that just like the battery, the zener will only draw as much current as necessary. And as you point out below, by the time the battery is close to fully charged, it is not drawing that much current.



> Ofcourse it will only happen after battery is nearly fully charged, but how can you even dissipate that much???


No need. At that point the current draw is only 1-2% of the Amp/Hour capacity of the battery. So somewhere between 1-2A for the MAXX 29's that you have.



> While my oversimple thing dissipates only 16w (2v at up to 8A) and only while battery is charging. Once it reached 14v - current drops to ~1A, which is 2w of waste. To charge 50% DOD 125AH battery - i waste appr 130wh per battery. Which calculates to be much less than zener case.


Once again you've missed the point. The zener circuit is in parallel to the battery. So it'll only draw current at the same rate as the the battery is drawing, and it'll only draw at a voltage in excess of the zener breakdown voltage. The rest of the energy is still used to charged the battery. The key point is that the zener shunt draws no current as long as the terminal voltage is below the trip point. So when the current draw is the highest at the beginning of the charge cycle, no current is being drawn across the shunt. So all of the power (at the full 8A initially) is going directly into the battery.

With the diode drop regulator dropping from 16V to 14V you
get at the start of the cycle [email protected] = 16W and at the end [email protected] = 2W.

With the shunt the initial terminal voltage of the battery is going to be somewhere around 12.5V. When you turn on the charger, all [email protected] goes into the battery. The terminal voltage will start to rise. Presume that the zener trips at 14V. Up until the point that the terminal voltage is 14V, it draws no current.

Eventually the battery gets to the 14V point. At this point it's at a 80% SOC and drawing something like 3A of current. So the terminal voltage continues to rise. The zener now kicks in and starts shunting to keep the voltage of the terminal at 14V. What you have missed here is that the battery is still charging. So that [email protected]=6W isn't completely shunted. The battery still drags the terminal voltage down to 14.1, 14.2, or 14.3V. So the zener only shunts the difference between the terminal voltage the battery rises to and 14V (i.e. 0.1, 0.2, or 0.3V @ 3A).

As the battery continues to charge, the current draw continues to drop. Eventually it'll drop off to under 1A though the terminal voltage at this point is somewhere near 14.5V. The shunt is still only shunting the difference in the terminal voltage and 14V at that less than 1A.

Now the charger still needs to be turned off, otherwise you're still wasting power. But unlike the series diode drop, the shunt kicks in when the battery has already mostly recharged, so most of the power of the charger went into the battery, not into the shunt.

I hope this clarifies.

ga2500ev


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## Sunking (Aug 10, 2009)

Stunt Driver said:


> One more, about charging with high currents - I know people been saying it is good for batteries, but I don't believe. It is not proven!
> 
> Solar banks leave long time - because they NEVER get high-current charge, it's just not available from PV panels.


That is not accurate, in fact exact opposite. Solar systems only get a few hours each day to recharge to replace what was used, so you have to run high charge rates. How high depends on your location and solar insolation in the winter, If you are unlucky and live in a place like Seattle you only get 1.1 Sun Hour per day in winter. 

So in Seattle if you use 1 Kwh per day, and design to a 5 day reserve capacity at 12 volts you need a 416 AH battery. With 1.1 Sun Hour and accounting for system efficiency you need a 1400 watt solar panel which means a carge current of roughly 100 amps or a C/4 charge rate to replace 1 Kwh in the battery.


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## Stunt Driver (May 14, 2009)

ga2500ev said:


> As the battery continues to charge, the current draw continues to drop. Eventually it'll drop off to under 1A though the terminal voltage at this point is somewhere near 14.5V. The shunt is still only shunting the difference in the terminal voltage and 14V at that less than 1A.


Thanks for link.

I guess in your description you are assuming a 3-stage charger used?
While I'm aiming at using 16.6v 8A power supply. 

If at 14.5v battery draws 1A, then remaining 7A have to be shunted, or voltage will go up on battery lugs. 
But still I have to recalculate: if battery is charged, and power supply sits at 16.6v, and ZD has to dissipate 7A, this would be 18W of power (all voltage above 14v). Not too bad now. Can you point me to the right zeners now please?


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## ga2500ev (Apr 20, 2008)

Stunt Driver said:


> Thanks for link.
> 
> I guess in your description you are assuming a 3-stage charger used?
> While I'm aiming at using 16.6v 8A power supply.


No. I know exactly what you were talking about.


> If at 14.5v battery draws 1A, then remaining 7A have to be shunted, or voltage will go up on battery lugs.


No. That's not how it works. 8A is the maximum current the charger can supply. It has no obligation to provide that amount of current at all times. Try a though experiment. Say you take a LED and a 1K resistor and tie it across your laptop supply. The 1K resistor will limit the amount of current that can be drawn across the supply to 16V/1K = 16 mA. Even though the supply can supply 8A, only 16 mA will actually be used.

A charging battery is like a potentiometer providing a variable resistance. A fully discharged battery will provide a low resistance path and will draw a lot of current. But as the battery gets closer to full charge, it draws less and less current from the supply.


> But still I have to recalculate: if battery is charged, and power supply sits at 16.6v, and ZD has to dissipate 7A, this would be 18W of power (all voltage above 14v). Not too bad now.


Correct on the voltage. Still not current on the current. At that point the battery will only be drawing an amp or so of current, because if the current were more, then the battery is more discharged, and so the terminal voltage would be lower than 14V. 



> Can you point me to the right zeners now please?


BG Micro has 8.2V and 6.2V 5W Zeners for less than a dime apiece. You can find them here:

http://www.bgmicro.com/index.asp?PageAction=VIEWCATS&Category=120&Page=1

Please pay attention to the fact that you need the 12V auto lamps to burn the excess power.

ga2500ev


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## Stunt Driver (May 14, 2009)

let's proof my understanding of yoru power supply theory first. by numbers.

Power supply, ideally, will hold 16v at up to 8A. But it's not perfect, so max Amps will go down a bit before you ger close to 16v. I have done rough measumerents - here it is in graph.

Around 14.4v it (deleted: is still able to) DOES give out about 7A. Guess my calculation holds?


IF you will put LED, or other high resistive load - curent will drop, but voltage will go up. 

My assureness - knowing graph below and voltage across power supply connected to load - you can definitely calculate Amperage. You agree?


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## dtbaker (Jan 5, 2008)

Stunt Driver said:


> Around 15v it is still able to give out about 7A.


...still 'able' to output 7a-8a is the key there. as a battery approaches full charge it cannot ACCEPT as much current. The voltage in Lead batteries gets up to a point, can't take any more charge, and will start heating up and 'gassing'. Li batteries will heat up also, and if they start gassing, you'll probably ruin them. 

The smart chargers tell when batteries reach a desired voltage setpoint towards the end of charging, and start cutting back available amps to HOLD the voltage at a safe level. At some point almost no more current can be added without the voltage going up, so the charger stops.


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## Stunt Driver (May 14, 2009)

Not sure are you just restating what is above?

From Ohm law it is clear that if battery "can't accept that current" - voltage will go up. If voltage is not up - battery is accepting current (good or bad it is) or something is shunting that current. Let me refrase that "still able" to - "does give out 7A per graph attached"

But if you put zener to keep voltage at 14.4v across battery - power supply will give out 7A granted. Zener will have to shunt ~6A, dissipating about 12W.

If a bult used in series with zener to dissipate that power - it has to be able of passing same 6A without much voltage drop, so 14.4v limit holds. That is where I'm lost - what type of bulb must it be?


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## dtbaker (Jan 5, 2008)

Stunt Driver said:


> Not sure are you just restating what is above?
> 
> Ohm law says that is battery can't accept that current - voltage will go up. If voltage is not up - battery is accepting current (good or bad it is). Let me refrase that "still able" to - "does give out 7A per graph attached"



no.... let me re-phrase. 
if the power supply is holding at 14 volts, it will NOT continue to pump out 7 or 8 amps. As the battery 'fills up', there are no more electrons to move across the plates, and the amps drop to 'nothing'.


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## Stunt Driver (May 14, 2009)

My power supply is 16.6v. What will hold it at 14v?

ps. let's not talk about smart chargers here. I am trying to adopt existing power supply to be used as CV charger. Discussion point is around how to make 14.4v CV charger out or 16.6v power supply. Diodes in series work, but aren't elegant solution


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## dtbaker (Jan 5, 2008)

Stunt Driver said:


> My power supply is 16.6v. What will hold it at 14v?
> 
> ps. let's not talk about smart chargers here. I am trying to adopt existing power supply to be used as CV charger. Discussion point is around how to make 14.4v CV charger out or 16.6v power supply. Diodes in series work, but aren't elegant solution


well.... if the charger is not a settable variable voltage with a knob on the front, then you DO need to find a way to limit the voltage to 14.4 for a 12v nominal lead battery, and maybe a little lower than that. If you hold the voltage at 14, the amps will take care of themselves.


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## Stunt Driver (May 14, 2009)

right, that is why I added Diodes, to limit voltage. And I see current will settle at less than 1A after overnight. Surely i don't want to leave this plugged in for a week, but I don't need charging to be that universal. Also, with diodes in series, unlike ZD in parallel, I get lower charge currents when battery is getting closer to full charge. And this seems to be good for battery. 

I'll be monitoring performance, and comparing with smart-chargers. Just want to share cheap BKMs with community.


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## ga2500ev (Apr 20, 2008)

Stunt Driver said:


> let's proof my understanding of yoru power supply theory first. by numbers.
> 
> Power supply, ideally, will hold 16v at up to 8A. But it's not perfect, so max Amps will go down a bit before you ger close to 16v. I have done rough measumerents - here it is in graph.


Good to see.


> Around 14.4v it (deleted: is still able to) DOES give out about 7A. Guess my calculation holds?


Not exactly. As the zeners kick in, it'll act the same as if you have switched your series diodes into the circuit limiting your voltage to the zener limit. So what will happen is your amps will jump from the charger only (the blue line at about 6A) to the charger + the diodes (the red line at about 1A). Note that the amperage draw is significantly less with the diodes in the circuit.

The difference is that charging will stay on the blue line until the zener voltage limit is reached.

So you get the best of both worlds: full power charging at the beginning of the charge cycle, and CV charging towards the end.

The bottom line is that you get exactly the same effect that you were looking for with your relay circuit: diodes out until a voltage threshold is reached, then diodes in to limit the voltage until charging is complete.

Good chart. Illustrates the concept quite well.

ga2500ev


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## Stunt Driver (May 14, 2009)

Got to nail this one

So what you are saying, is with wiring as below, current from power supply will act like shown on graph below?
Will power supply voltage reach it's 16v at idle load?


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## ga2500ev (Apr 20, 2008)

That is close to the correct behavior. The brown part of the line after the zeners kick in may not be perfect because the zeners voltage limit the terminal voltage. So the terminal voltage will never actually rise above whatever the limit is. The problem is that if the charger is left on continuously, the amperage through the zeners will continue to rise eventually burning them out. BTW I continue to remind you that you just cannot tie a zener across a power source because it'll cause a dead short. Lee Hart uses the PR2 auto lamps as a current limiter and energy burner for the shunt. So once the zeners kick in, the shunted energy lights the lamp.

Lee Hart recommends turning off the charger so that the shunt doesn't burn out which would cause the batteries to overcharge.

The one item that's unclear to me is how to operate this shunt in a single battery environment. Lee Hart originally designed this system as a balancer for a battery pack and a single high voltage charger. So say you have 3 12V batteries and a 36V charger. Each battery would have a shunt. If they are unbalanced, then one battery will have a higher SOC than the others and its terminal voltage will trigger first. The shunt kicks in and starts diverting power around that battery to the others that have not fully charged yet.

In a single battery environment, that power is shunted to ground. So it's burned off in light and heat into the lamp. But since the trigger voltage is above the battery resting voltage, the battery continues to charge, so it's terminal voltage continues to rise, while the charging current drops off. What is unclear to me is if at some point, the zener/lamp actually starts pulling energy out of the battery and burning it.

I'll try to do a test setup this weekend with a new 12V 7A gel cell I just got and a couple of 5W zeners (if I can find some in town).

ga2500ev


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## Stunt Driver (May 14, 2009)

rephrased:



> So the terminal voltage will never actually rise above whatever the limit is.


I agree, that is the whole purpose of ZD.

Per PSU output graph few posts up - at 14v PSU *WILL* give out 7A. There is NOTHING in the world to stop PSU giving out 7A except voltage>14v across it's terminals.

Next question - where will this current go?


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## ga2500ev (Apr 20, 2008)

Stunt Driver said:


> rephrased:
> 
> 
> 
> ...


I do believe I'm starting to see your point. In Lee's original application, the shunt would route around the battery and feed the power to another battery that was still charging. In the single battery case the shunt would have to drag the supply down to the trip point forcing the supply to put out 7A of current. While the battery would still charge at 1A, the other 6A of current would still need to be shunted though the zeners. Not a good look.

So it seems that the power rectifiers are still needed and that your current approach of them always being in the loop is a simple and effective strategy.

My plan is to still implement a microcontroller based manager that measures both terminal voltage and battery charing current.

Glad that we had this discussion. Good luck with your project.

ga2500ev


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## Stunt Driver (May 14, 2009)

Thanks, I think it always worths gettin got the point.

By the way, one of my over-smart Schumacher chargers just failed me! Pack was somewhat nearly full, but I wanted it charged all the way, because needed to drive almost the full range at lunch. So I set smart chargers to 12A. But being a SMART charger, one of 4 decided that voltage rose too quick on battery, and has switched to some very low cahrge, like 0.5A or so. 
That is how I ended up with 1 out of 4 batteries well behind in SOC. Other 3, that sit on CV - were happy and charged, ofcourse.

That is where you have two ways: do something bullet proof, like CV for free, or buy a proper high voltage charger, smart in a good way and expensive.
I choose first for convertion, and still waiting for Aptera to ramp, and bring me my #2224 reservation "Aptera 2e"


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