# Lead Acid Charger on lithium batteries



## BMI/LiFeTech (Aug 12, 2009)

Many of the lead acid chargers can be used to charge a LiFePO4 pack but there can be problems. Most often the problem is the end of charge voltage for the lithium pack is higher than that of an equivalent nominal voltage lead acid pack. You need to work on an end of charge voltage of 3.65-4V per cell for the lithium pack (depending on manufacturers specs) and check that the lead acid charger will reach this end voltage. 
The main issue is that due to the flat CC/CV charge/discharge curves of the lithium pack, if the lead acid charger is only a few volts under the recommended lithium battery end of charge voltage, the lithium pack may fall well short of full / 100% charge when the lead acid charger is used and thus you will not be able to fully recharge the pack.


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## hardym (Apr 2, 2008)

Yes, a LA charger will work on Lithium. 

The LA charger for Flooded LA will run to 2.6 volts a cell. so a 48 volt FLA charger will run as high as to 62 volts. 

LiFePo4 cells can be charged anywhere from 3.6 to 4.2 volts. There is very little energy added to the cells between these two voltages during charging. It allows balancing based on the charger profiile. 

The Li charger needs to reduce current when the average cell voltage reaches 3.6 or so to allow balancing. 

Your BMS needs to be adjustable to this threshold and balance when the current is reduced. 

So any CC/CV charger can be used for Lithium, the BMS will need to monitor and cutoff when any cell reaches max voltage (4.2v).

Mark
Hardy EV
ConvertTheFuture.com


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## JimDanielson (Oct 19, 2008)

Would it be ok to use the 84 volt charger then?


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## JimDanielson (Oct 19, 2008)

How does a BMS work (i would be using the volt blocher)? Once that cell reaches full voltage, does it act as a wire and just allow electricity top pass to the other cells in series or does it do something different?


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## neanderthal (Jul 24, 2008)

The voltblocher (and most others) actually just turns the extra energy on any cell reaching a certain voltage to heat. It heats up a little heatsink, it doesn't transfer it to another cell.


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## _GonZo_ (Mar 23, 2009)

jimbo12d said:


> How does a BMS work (i would be using the volt blocher)? Once that cell reaches full voltage, does it act as a wire and just allow electricity top pass to the other cells in series or does it do something different?


A BMS is a Batery Monitoring System, what it does is control the battery paramenters, some are very simple, they just balance the cells, control min/max voltage of the cells and power in/out.
More sophisticated ones are fully programable and can record battery life, charges, discharges, take care of the charge, etc...


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## 86Honda (Apr 15, 2009)

I used my BC-20 charger for both my old FLA pack and my new LiFePO pack. It helps that the BC-20 is both current and voltage adjustable. It will taper down to about 4 amps or less after being carefully watched and adjusted on the first charges. VoltBlochers take care of overcharge (and help heat up my battery boxes). So far the system has worked well and requires little care after setup.


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## Voltswagen (Nov 13, 2008)

If you watch Jack Rickard's video on charging LiFePO's (EVTV) he suggests not charging them to full voltage anyway. I believe his cutoff is at 3.9 or 4 volts max. This extends the life of the pack at a greater percentage compared to the few miles of lost range.


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## paker (Jun 20, 2008)

He's also is against battery managment systems, calling them "dangerous".


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## Voltswagen (Nov 13, 2008)

Paker
Yes, you are right Rickard doesn't believe that the current BMS systems are worth the expense and could actually damage the Lithiums.
But......look at his charger......it has adjustable voltage and a mighty high price tag.


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## MN Driver (Sep 29, 2009)

He is against them because the BMS systems discharge the excess current as heat, which he says that in his experience has started a fire or fires due to getting far too hot.

I agree with him when he says that shunt balancing on every charge isn't neccessary but the most important part of the BMS is that it is a safety device, it will cut the charger if voltage gets too high for a single cell or shunt the amperage preventing such a thing from happening, and while discharging it will prevent the lowest cell from dropping below the death voltage point.

Personally what I'd like to do is balance my cells well enough to be able to just have a BMS that cuts down the charger amperage down to keep the max voltage in check for the highest voltage cell and terminate the charge when the charger current is at the ending level. That way you aren't burning off and wasting electricity as heat to keep all the cells at the top. When discharging while driving I'd prefer to monitor the cells and if they seem out of balance then the chance could be used to do a manual balance or use the balancing shunts as neccessary but not on every charge as charging to 100% SOC is not neccessary with a new pack if you give yourself a good 30% of play in your range. Then possibly use the shunts to balance them after every few weeks if your car is a daily driver. From the info I seem to be coming across, getting the pack to 95% of SOC doesn't need you to be running past even 3.7 volts and pretty much every manufacturer of LiFePO4 cells that I've come across, with Thunder Sky excluded have a max charge voltage rating of 3.6 or 3.7 volts for LiFePO4 chemistry. I'm still convinced that the 4.25 max voltage charge is a safety factor but ignores max cycle life factors. With the Lithium Ion Cobalt technologies that the Tesla uses they discuss ending charging voltage at 4.1 volts(or even lower) instead of the 4.2 volts for Lithium Ion as it provides additional life of the cells if you don't need that extra little bit of range, but keep in mind that is standard LiIon not LiFePO4. I think that working with 3.6 volts may extend the life of the pack. How much additional Ah percentage is there from 3.6 through 4.25 on a Thundersky cell if you were to charge to 3.6 volts at C/10 and 4.25 volts at C/10 as well. C/10 is the right ending amperage for these right. Do we have any numbers. If not 3.6, then maybe 3.7 is better because there really isn't anything there from 3.7 through 4.25 from what I've come across. The testing I've seen for the Sky Energy cells seems to demonstrate that from 3.59 to 3.76 volts there is only a 3.5% additional capacity that is pumped into the cell while charging and their rated max is 3.6 volts, directly past 3.6 the voltage spikes on Sky Energy cells. Those cells are a bit different than the Thunder Sky cells though.

When I end up putting my EV together, I'll be oversizing the cells to make their lives easy with lower C rate discharges, a more capable pack at lower temperatures(even though I'd use a battery warming solution for charging and for the first leg of a trip with a well insulated box to hopefully keep them decently above freezing temps with -20f temperatures outside for about 11 hours which is the worse case daily scenario while at work) and also when the packs come towards the end of their life, I'd like to still have room so I'm not running 100% DoD all the time. Then maybe after 3000 cycles if I'm lucky and I still get 80% of the capacity when the wheels fall off the car I'm driving so to speak I can take my controller, motor, and pack and migrate to the next(likely newer) car to convert without too much cost when it comes to the next vehicle.

Basically, my plan is to oversize things so that the maximum distance that I plan to go only brings me to 70% DoD, but without knowing the full power needs of my setup, I need to overplan from even that point. I'd prefer a pack that can manage 100 miles if I need to stretch it. My daily commute is 30 miles, so I could manage to charge every other day. With 100 miles I could drive into Minneapolis from where I live or work and back to home on the same charge or drive to friends houses farther away on the same charge as work and still make it home. 100 miles really is the longest theoretical daily trip for me if I'm not going on a road trip somewhere else, it's a long stretch for many people with EVs and a HIGH cost at this point for anyone who wants to do it at 80% DOD too!

I do have an advantage at the moment, I won't be doing an EV conversion for at least two years so it is possible that the current drop in cost for LiFePO4 cells will continue as well as better volumetric, power and weigh advantages that may come up. I'm currently looking at the HPGC AC50 system with a absolute max voltage of 130 volts for the controller. With the Sky Energy cells and their top charge voltage at 3.6, I could use 36 cells and be at 129.6 volts or use less cells since it's a regen package. I'd want an additional few cells in case I have failures, but since the system was designed around 96 volts it wouldn't damage performance much, just range. If I went with Thundersky cells I'd stick with 35 or 34 to use in my pack. I figure with a super light and aerodynamic vehicle such as the Honda Insight(also rustproof) or something lightweight like the Toyota Echo or Tercel to seat more than 2 then I could accomplish reasonable power with the 50 peak HP and slightly over 100 ft-lbs of torque available. At 200 Ahr with those cells, if the 1800 pound(with gas engine) aerodynamic car with LRR tires can manage 200 Whr a mile with a 35 cell Thunder Sky pack(22,400kWh) it would top out at 112 miles with 100% DoD. This wouldn't get me the longest possible trip with the 70% DoD consideration but 78.4 miles would realistically be good enough for me and the pack isn't going to be hitting 3C even under max acceleration. ...but with the next size up using 35 260Ahr cells(29,120 kWh) if I figure a 5 seater 4 door car that is lightweight and gets decent gas mileage before EV conversion and can manage a more conservative estimate of 250Whr/mile, it would be 117 miles, and when figuring 70% DOD of 81.5 miles or 93.184 at 80% DOD, I could still manage 100 miles without hitting 90% DOD but I'd have to make sure I top off the pack before such a trip. ...but with a 200Whr/mile vehicle and setup, the 70% DOD could get 101.92 miles. With 260Ah cells and a max acceleration draw of the 550 amp controller, I'd only be pulling 2.1C which even during the winter, I don't need to be as concerned over voltage sag especially with the standard slower acceleration that is usually required with ice and snow too.

All of this comes at a high battery cost of course, it comes out to be $10k with a 35 cells of 260Ah or a little under $8k for a 35 cell 200Ah pack but the pack of either of those two sizes would hold up better and for longer with less amperage draw and shorter DOD draws, as well as being able to charge it every other day with the standard work commute taking it down to 60% DOD each time I charge. I just checked the Thunder Sky page and they are showing 0.5C as the standard charge/discharge and 5000 cycles at 70%. With a 260Ah pack, I would likely be cruising at 0.5C pretty much all the time unless I'm accelerating, passing, or climbing a hill(of which there are not many due to the glaciers passing through MN back in the day). I wouldn't be running below 60% on a regular every other day charge basis but even if I did charge every day and got 5000 cycles, we come out to 13.7 years, or for an every other day charge 27 years. Do I think they really will get 5,000 cycles, probably not, but I'd be incredibly content if they did!! The only concern I'd have is that as cells age their internal resistence rises meaning that higher C rates are more difficult to obtain which is also a reason of why I'd oversize the pack other having the pack be able to work with a car that would get 250Wh/mile. It provides me a very generous amount of room beyond when the pack only gives 80% of its original capacity and less amperage draw capability.

One thing I'd have to be very sure of is that I could live with the same or similar low voltage modestly powered AC setup for the life of the pack because raising the voltage of a pack like this would be -very- expensive with this cell size but worst case scenario I use a high amperage DC setup to replace it to work with the lower voltage.


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## Voltswagen (Nov 13, 2008)

MN
Because these Lithiums have such a high price tag and longevity it may be wise to purchase a few extra cells over what you will actually need. 
The chemistry and voltage may change in the next 5 or 10 years and we may not be able to purchase replacements of the battery type needed should a couple of cells fail during the life of the pack.
Just my .10 cents


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## MN Driver (Sep 29, 2009)

Voltswagen, I must have forgotten to mention that but it is part of the plan. I plan to have a few extra, perhaps having 38 cells, using 35 but knowing full well that I could operate using 34 cells leaving a decent 4 more than I really need, without much loss or possibly even less in a worst case scenario if I were lose 4 or more cells which would be factoring a 10% failure rate which hopefully doesn't occur but I would be preparing myself for. I figure if there are any serious issues that I would know in the first year and be able to still purchase more as well if needed but with the at least two to four years or so of time to be sure my finances are plenty ready for a conversion I can find out how well these may seem to fair over that time. I'm also waiting to hear from people using these in real world EVs with their cold weather characteristics of the cells which is something I'm very curious about, even though I plan to heat them during charge and the first leg of a trip and have well insulated boxes to protect them better than most probably will be doing or need to do.


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## Voltswagen (Nov 13, 2008)

I'm sure you will make the right choices as you seem to have thought this through.


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## czwbattery (Oct 13, 2009)

The Charge is ok. Problem not voltage, but currency.

Like 12V, 10A battery pack, you can use 9~~15V even, 20V charges for input/output, but the currency should be liminted. 

The PMC or MS is non of business. So it will be short or explored. So much attention to the currency.

www.czwbattery.com


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## czwbattery (Oct 13, 2009)

EV Lithium Batteries,

most of EV lithium batteries use the Li-Fe batteries single Square cells or Cylindrical Li-Fe batteries cells:
Li-Fe Cylindrical cells: 18650, 26650, 38120, 32900, 32600, 42120, etc.

Singgle Squre cells: 3.2V , 10A, are most particular.
Also, 3.2V, 50A, 3.2V 100A, 3.2V, 400A, 3.2V 180A, etc.

EV Battereis are much different Lead Acid.

So when you charding or discharging, please do use the lithium batteries.


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## _GonZo_ (Mar 23, 2009)

> He is against them because the BMS systems discharge the excess current as heat, which he says that in his experience has started a fire or fires due to getting far too hot.


There is different tipes of circuits for managing batery packs.
As simple as a volt watcher that just burns extra current when voltage reases certain level.

Others that control each cell voltage and when any of the cells reaches maximun voltage cuts down the charge as well they monitor the voltge on discharge and if any of the cell goes under the limit, shuts down the out put.
This are usually called PCM and are used on phones, computers etc.

The next level is BMS that as comented before can be very simple or very complicate.
Any way just to let you know there is two ways the BMS control the balancing of the cells.
One tipe is the one you describe that burns the extra power (Like the volt wathchers) That are ususlly called resistive balancing.
And another tipe is the ones that redirects current from the cells that are higher on voltage to the ones that are lower. That are usually called capacity transfer balancing.
Depending on the use and mainly on the charging sistems one or other tipe is used.


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## MN Driver (Sep 29, 2009)

_GonZo_ said:


> And another tipe is the ones that redirects current from the cells that are higher on voltage to the ones that are lower. That are usually called capacity transfer balancing.
> Depending on the use and mainly on the charging sistems one or other tipe is used.


I just made a thread asking if something like that was possible and pretty much everyone who commented on the thread said that it would be extremely expensive and wasteful for power if something like this was put together and used. I haven't seen this used on any EV conversion using a standard charger accessible for most of us that I've come across yet.

You mention high and low voltage used to step down charging and discharging, I already plan to use something like that because I would have to in order to use shunts, especially when charging a cell pack of 35 200Ah cells or so when the C/20 rating is at 10 amps. If I reached the LVC cutoff when driving I'd probably just want the system to shut off since the pack is near dead as it is and if I'm watching things, I'll know it's coming anyway.


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## Voltswagen (Nov 13, 2008)

Oh goody! Another Chinese battery ad with no prices.
Hey James....you want to get our attention? List the pricing for prismatic 100ah and 200ah........and *DON"T* send me an email thank you.


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