[speculawyer]

Dave Kois has done a wonderful job of establishing a good pipeline to Chinese-made LiFePO4 batteries. See here:
http://www.evcomponents.com/SearchResults.asp?Cat=28

With LiFePO4s now costing less than $350/KWH, is there really any point to getting lead-acid batteries anymore? Granted, the LiFePO4s are still more expensive than lead-acid, but the fact that they are supposed to be good for some 2000 cycles means that they should easily last more than twice as long as a lead-acid set.

I think the only advantages of lead-acid at this point are:
1) Upfront price . . . they are less up front, but in the long run they will cost more.
2) Durability - Lead acid batteries can be abused and over-charged and they'll still work fine. LiFePO4s are much more sensitive. If you over-charge them or over-discharge them, they may die.

But (2) can be addressed with a good Battery management system. And this is the only area where I see real weakness in lithium-ion batteries. The available Battery Management Systems are crappy, expensive, flaky, and/or not easy to use. If someone produces a good inexpensive mass-produced easy-to-use Battery management system, I really think lead-acid is on its last legs.


This idea came to me when I was looking at helping someone deal with an NEV having battery issues. To replace a full set of 6 12-Volt lead acid batteries for an NEV can be pretty expensive. If you get good deep cycle marine batteries, they can cost close to $200 a piece. And since they are so damn heavy, you know the shipping will push them to that $200 price such that a full set of six batteries for a 72Volt based NEV is $1200.

Well, if one picks up 24 of these 60 Amp-hour lithium iron phophate batteries, the total price is just $1584:
http://www.evcomponents.com/ProductD...de=TS-LFP60AHA
$1584 is just a little more expensive than the $1200 price for a full new set of lead-acids. But that is more than made up for by the longevity, lighter weight, and improved performance of the LiFePO4s.

But the problem is that you really should have a BMS system. You can probably get away without one for a while (Just hook up the 24 cells in series and charge them up . . . maybe even with the existing charger.). But if you do that, you are taking a risk. If one cell shorts out, you may end up over-charging the others thus destroying the whole pack.

If someone made an inexpensive BMS, I think lead-acid would start going away.

[JRP3]

Actually I'm seeing pretty good evidence that a cell level BMS is not necessary if you keep well within the discharge/charge parameters. Jack Rickard has made a pretty good argument to split your pack in half and monitor each half. As long as they are equal you know they are in balance, and as long as you don't pull high C rates they should stay in balance.

[jorhyne]

Another trick I have heard of is occasionally (or at least initially) is to equalize all of your batteries by connecting them in parallel and charging them as one big 3.2 volt battery. Once they are fully charged rearrange them back into your series alignment and supposedly they will stay close to balanced for a good while.

[speculawyer]

Actually I'm seeing pretty good evidence that a cell level BMS is not necessary if you keep well within the discharge/charge parameters. Jack Rickard has made a pretty good argument to split your pack in half and monitor each half. As long as they are equal you know they are in balance, and as long as you don't pull high C rates they should stay in balance.

I figure that an NEV that ran on lead-acid batteries won't really stress a LiFePO4 cells. And if I periodically test the cells and manually balance them somehow, I would think it would work fine.

Originally Posted by jorhyne

Another trick I have heard of is occasionally (or at least initially) is to equalize all of your batteries by connecting them in parallel and charging them as one big 3.2 volt battery. Once they are fully charged rearrange them back into your series alignment and supposedly they will stay close to balanced for a good while.

Is there some kind of special charger for this?

[JRP3]

An adjustable 5 volt power supply should work, though it might take a loooong time to get it done unless it's a high current unit. I suppose you could charge the pack in series to maybe 3.5V per cell or so then finish off in parallel for the final charge to 3.6. You would need to monitor closely during the series charge because if one or more cells is at a significantly higher SOC they could start overcharging before the others are done.

[sunworksco]

A BMS system is so easy to install on your individual batteries.Why is everyone here getting their shorts in a bunch?

[dimitri]

Originally Posted by sunworksco

A BMS system is so easy to install on your individual batteries.Why is everyone here getting their shorts in a bunch?

I think its the fact that with LiFePo4 prices being lower nowdays, the cost of BMS becomes significant part of overall cost, so naturally people are looking for cheaper alternatives, nothing wrong with that.

And what do you mean by "easy to install" ? This is too general of a statement. Does that include charger and controller integration with BMS? Because there is nothing easy about it these days since chargers and controllers are all different. If you are referring to a simple shunting / balancing BMS, then yes, its easy enough, but many people want more safety / protection than that.

There are many opinions on BMS, ranging from complete ignorance to ridiculous overkill, so until there is a standard off the shelf system that is widely accepted by most users, these discussions will live on

[Bowser330]

I hope they continue to drop, the prices of LIfepo4s that is...

Also whatever happened to those optimized lead-acid batteries e.g. firefly?

BMS,

Say I wanted to install a small genset (240V & 20A 5kw) can a BMS balance the charge and discharge profile of cells at the sametime...say I wanted to charge my pack (via the Nivan charger) while I was driving...

[sunworksco]

People on this forum need to study and play with RC planes,rock crawlers,boats.These are small versions of ac motor drivetrains with lipo batteries,balancers,contollers and chargers.Learn inexpensively before you take the expensive plunge.No one ever said evs are cheap except the no fear blissfull ignorant ones. This is not to say that skills are not required but they can be obtained if you research the subject.You need a smart pc sensored contoller/charging system and balancer harnesses installed on individual batteries connected to a battery balancer to keep minimum/maximum voltage levels.This is needed for charge/discharge and brake regeneration.A pc tablet to anaylise the controller/motor/BMS system is required as well and can be used for your gauge cluster.This is not a black art and anyone with electrical skills can obtain.

[dimitri]

Originally Posted by Bowser330

Say I wanted to install a small genset (240V & 20A 5kw) can a BMS balance the charge and discharge profile of cells at the sametime...say I wanted to charge my pack (via the Nivan charger) while I was driving...

If you use genset AC output and connect it to the charger AC input, then everything after charger looks and works the same as if it was plugged into the garage outlet, i.e. charger will slow down at the end and your genset will pretty much waste fuel running idle.

However, in real life you will never get to the balancing stage via genset during driving because you will spend energy 5-10 times faster than genset puts it back, so it will always be below balancing voltage levels.