# Big deal to switch from LIFEPO4 to deep cycle?



## Ziggythewiz (May 16, 2010)

What sort of mishap was it?

No one switches from lithium to lead. You'll have less capacity and more weight giving worse performance and less range.

In addition to needing a new charger, you'll need new battery mounts and possibly brake and suspension upgrades.


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## Elithion (Oct 6, 2009)

willitwork said:


> Any drawbacks to making such a switch?


Honestly, Li-ion is not for everyone. Lead Acid may be a better match for some users: fewer hassles, no fancy equipment required, cheap, forgiving.

I say: go for it. Many of us have years of experience with Lead Acid, and you'll be able to draw from that experience.


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## Siwastaja (Aug 1, 2012)

Please share your mishap so that others can learn from it. There is too little actual data available on lithium installation failures on these forums. It could also help if you define what "no luck" means. Performance problems? Range problems?


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## dragonsgate (May 19, 2012)

Ziggythewiz said:


> What sort of mishap was it?


Yes I too would like to hear more details about your lithium problems. There are many of us that have not switched to lithium for various reasons and are still on the fence when it comes to lead Vs. lithium. If you have been running lithium for any amount of time I would imagine lead is going to be a let down in many ways. Right off would be the extra weight and lose of range.


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## onegreenev (May 18, 2012)

My Hi-Power cells were made in 08 and still working fine. They were purchased used and abused but still work great. Little magic boxes. Even the worst of the Lithium is better than the best of the lead. I'd almost bet he has not bottom balanced and has used a crappy BMS and has lost cells in the process. Since he gives no real explanation I can only suppose and speculate but since I have old Hi-Power that are old but still usable I see no reason to abandon the LiFePO4 cells. 

Hogwash to switching to lead acid. Just utter hogwash.


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## dragonsgate (May 19, 2012)

Ziggythewiz said:


> In addition to needing a new controller, you'll need new battery mounts and possibly brake and suspension upgrades.


 Why a new controller?


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## Ziggythewiz (May 16, 2010)

dragonsgate said:


> Why a new controller?


Sorry, meant charger.


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## dragonsgate (May 19, 2012)

Ziggythewiz said:


> Sorry, meant charger.


You are forgiven.


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## willitwork (Apr 9, 2008)

Hmm, thats good information that your Hipower are still fine. Mine are also as old, and I've had a few replacements that were newer.

The extra weight is no problem as the batteries are in a pickup truck. My main thing is cost and the apparent lack of quick availability for replacements. A few weeks delay before they would even get here. I got my cells originally from cloud electric when they were in 'cahoots' with LionEv. then got some replacements at lithiumstorage.com. If you know of a legit place where I can get replacement lifepo4 at a reasonable cost/delivery time, I would probably stick with lifepo4.

As far as a bad BMS, i dont think so, I am using BEQ, and paktrakr for monitoring. I had already asked zivan about reprogramming the charger, but didnt hear back.

My experience with the lifepo4 so far has not been good, the last failure was all my fault as I re-located the batteries to where they was no ait circulation. They were originally under the truck bed, but because I had an extended cab, several were out of reach when I needed to access them, so I moved them.


Maybe i'll stick with lifepo4 if I can truly find some good ones.
thanks


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## Siwastaja (Aug 1, 2012)

So what happened? Why did you need replacements? You still failed to answer that.


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## onegreenev (May 18, 2012)

Finding 08 replacement cells may be a bit difficult locate. Most are newer and not the same as the older ones. Most failures would be due to overdischarge or overcharge and not because they were placed where there is little circulation of air. LiFePO4 actually do well when quite warm. No real need to try to keep them cool. The trick is to keep them warm. Mine were originally abused because of faulty factory BMS systems connected to the packs. I got a pile of them for an excellent price and came out with some pretty good cells. I do however have some that are not so good. Usable for my Cushman but not for my car. I sold some, traded some and still have 62 good ones and 24 so so ones. 60 will be in my VW Roadster. 

Pete 

So what was the failure? Bloating? Melting? Stripped threads? Or just quit working for no apparent reason? Or other?


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## Siwastaja (Aug 1, 2012)

Lithium is easy in a sense that, due to non-existent Peukert effect and very little self-discharge, there is no reason why you couldn't mix different brands and ages of cells when connected in series, i.e., all have 100% charge efficiency (= Ah efficiency), and when the same current goes through them all, they stay in balance regardless of differences in resistance or capacity. Of course, all of them need to be good enough to be usable in terms of internal resistance and capacity, but that's about it. (Very poor ones may overheat.) A digital BMS would come very handy especially with "shady" or cheap packs or packs with different kind of cells, but unfortunately it does not go along with the low cost.

Of course the cells can only be balanced at one point (top, or some prefer bottom) so there is always one cell that is the first to reach full or empty, but that is true to any battery system, even if they are the same brand and batch. No-BMS can possibly work but some people make it sound like an easy silver bullet to all problems, while in reality it needs really deep understanding of the system, and some careful fine tuning and monitoring. A BMS system, too, needs to be properly installed and their instructions understood. It has also been claimed that there are non-functional BMS's on the market, but with no product names, let alone proof, provided.

Lead acid, by the way, also needs deep understanding and possibly also some maintenance.

You just need to remember that we cannot take a role of a "customer" here. When you DIY a car, you need to really _understand_ the technology behind it. Battery technology isn't difficult, but you can't go passively around it either. You can get batteries that "just work", but they are pretty expensive. They are enclosed modules with li-ion cells and integrated, well-tested BMS.


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## onegreenev (May 18, 2012)

> No-BMS can possibly work but some people make it sound like an easy silver bullet to all problems........


True, going BMS free is not a silver bullet but neither is using a BMS a silver bullet. I chose no BMS due to a FACTORY BMS failing. I do not TRUST them. I trust the system I use. It is a proven system.


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## onegreenev (May 18, 2012)

> You can get batteries that "just work", but they are pretty expensive.


Actually you can't get anything that JUST WORKS. Everything requires some knowledge and instruction to setup and use.


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## Siwastaja (Aug 1, 2012)

I can understand that pretty well, especially when it's a relatively new market area with small players you can't know anything about.

I will build my own BMS for both the trust reason and for budget reasons. (Even if it failed, it would be at least a learning event.) No BMS is not an option for me, maybe except for very careful initial tests. One of the reasons is that the car may be used and charged by many people, some of them possibly non-technical.


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## Siwastaja (Aug 1, 2012)

Pardon a stupid question, but what is BEQ? I'm not very good with TLA's.


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## willitwork (Apr 9, 2008)

Siwastaja said:


> So what happened? Why did you need replacements? You still failed to answer that.


The failure was caused by my 'buffoonery' I had the batteries in an enclosed box with little to no air circulation. I usually do very short trips, so the heat was never a problem, but on my last trip, I was doing around a 26 mile round trip and the heat literally baked the batteries. Yes, I ignored paktrakr warnings. So I admit my stupidity, so I lost around half the batteries and need to make a decision to replace or switch.

I originally had the batteries under the truck bed. But ran into problems there SO i moved to a less than optimal location.


For the question on what is the BEQ. It specifically is the BEQ1 lifepo4 made by HOT Juice electric (which is now out of business).

And they ended up 'bloating' as the one person said.


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## onegreenev (May 18, 2012)

That nails the issue. Its not the lithium batteries that are at fault.


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## Ziggythewiz (May 16, 2010)

onegreenev said:


> That nails the issue. Its not the lithium batteries that are at fault.


Except that they seem to have overheated, which most LiFePO4 prismatics would be hard pressed to do.


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## dladd (Jun 1, 2011)

replace the bad cells, redesign your battery box, and move on. Don't move backwards to lead. I personally have a wide range of cells (some more damaged than others) and they are playing very well with each other (48 in series with Mini-BMS), I wouldn't hesitate to put in newer cells along side your still-good original ones. 

I bet it would be cheaper too, to just replace the bad cells. Cheaper than all new Lead cells, new charger, new hold downs, etc.


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## onegreenev (May 18, 2012)

> made by HOT Juice electric (which is now out of business).


No wonder they are out of business. You over charged your cells or you over discharged a very imbalanced pack that last time out. The heat was caused by cooking empty cells. That is the other way to bloat a cell or bunch of them. Its also the reason I have gone totally BMS free and bottom balance my cells and never have anything sucking juice from my pack unless its from the entire pack. You want no parasitic loads that will cause an imbalance on your pack. Keeping the packtracker operational requires partial pack power and tapping off the pack for that will cause a huge imbalance. 

The Lithium Cells you have are not the issue. Balanced cells will not overheat on a normal drive but if you loose a low one it will become scorching hot. A bunch of them will be even more so. Scorching hot enough to melt the plastic. I was lucky it only made the plastic pliable. Lost two cells because of an imbalanced pack. Improperly bottom balanced. I cut corners. Once balanced I never had an issue even in hot weather and even when I drove them hard and drive them to near empty. 

BMS free.


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## Siwastaja (Aug 1, 2012)

Are you really SURE the problem was with overheating? Or is it possible it is actually caused by *overdischarge*? It would make sense as your trip was longer than before. LiFePO4 cells should not abruptly die because of heat, unless it's very extreme. (And if your cells did heat up that much, they probably were already compromised.)

Overdischarge, on the other hand, can kill the cells _instantly_. You didn't have a BMS to save you from overdischarge. (A top balancer is not a BMS.)

Lead acid cells, by they way, also die when overdischarged. Not one-shot, but they do suffer a lot.


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## onegreenev (May 18, 2012)

Ziggythewiz said:


> Except that they seem to have overheated, which most LiFePO4 prismatics would be hard pressed to do.


 Half of them overheated and that comes from overcharging or over discharging. Ask me how I know. You will heat your pack to scorching hot if you overdischarge and reverse your cells. I am sorry there is no speculating on this one. He had an imbalanced pack and at the end of his last ride he had cells that emptied and he killed his imbalanced pack. His cheap balancers and BMS could do nothing to stop that. 

Like he said: His buffoonery. We all learn. Some learn harder than others. Bummer. But all is not lost.


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## onegreenev (May 18, 2012)

If the cells were all bottom balanced he would not have had an overheat problem due to over discharge. What happened is he drove a pile of cells into reversal. That is the problem. Imbalanced at the end of charge. That is the very reason you NEED to bottom balance. It has always been not if you drive your car to the end of charge but when you do. He did and had an imbalanced pack. If balanced they all empty and none go into reversal and all remain normal temps. That is a known fact.


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## Ziggythewiz (May 16, 2010)

You can't blame the manufacturer and the user at the same time.


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## Siwastaja (Aug 1, 2012)

As a general note.

Carefully analyze any problems to find the real cause. Ask for help in that. I'm pretty sure it's overdischarge, caused by the lack of control systems (BMS) and/or other instrumentation (Ah meter with enough leeway) and/or knowledge how to use the system (how long to drive without a BMS; some people manage to do that).

Doing a random move without analyzing the cause is going to add up your costs a lot. Doing the same mistakes again using the lead pack that would have even shorter range would kill that pack very quickly, too. Change it every year without knowing why it performs so badly. Or do a bit of research and get a well-performing lithium system that lasts for 10 years and pays itself back in a few years.

For lead acid, you don't usually use a BMS, but just carefully monitor voltage and try to avoid overdischarge; it doesn't come so quick and even if it does, it is not as disastrous.


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## Ziggythewiz (May 16, 2010)

Siwastaja said:


> Carefully analyze any problems to find the real cause. Ask for help in that. I'm pretty sure it's overdischarge, caused by the lack of control systems (BMS) and/or other instrumentation (Ah meter with enough leeway) and/or knowledge how to use the system (how long to drive without a BMS; some people manage to do that).
> 
> Doing a random move without analyzing the cause is going to add up your costs a lot. Doing the same mistakes again using the lead pack that would have even shorter range would kill that pack very quickly, too. Change it every year without knowing why it performs so badly. Or do a bit of research and get a well-performing lithium system that lasts for 10 years and pays itself back in a few years.


Good advice.


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## onegreenev (May 18, 2012)

Ziggythewiz said:


> You can't blame the manufacturer and the user at the same time.


Sure you can.


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## Siwastaja (Aug 1, 2012)

As a note concerning bottom-balancing.

It is a kludge known to help in a non-BMS system to avoid overdischarge pretty well. What remains unsaid by the proponents, is that bottom balancing moves the lack of protection from the discharge stage into the charge stage. As you do charging more frequently than full discharging, this issue needs to be addressed. Apparently, some bottom balancers have succeeded in setting charge voltage and/or using charge timer so that no cells are badly overcharged. But you need to get this right, otherwise you will destroy the cells in overcharging. This strategy works because of the fact that LiFePO4 can stand some overcharging, but it's not a silver bullet.

Only a BMS can really protect the cells in both charge and discharge.

Still, there is no known report of a failed BMS system; only rumors with no details provided. And, the rumors can be traced back to only a handful of people, which makes it a bit suspicious. So, always provide all the data. It's important.


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## Ziggythewiz (May 16, 2010)

onegreenev said:


> Sure you can.


Sorry. I should have been more specific. An intelligent person will not blame the user and the manufacturer at the same time. You are free to do whatever you want.



onegreenev said:


> No wonder they are out of business. You over charged your cells or you over discharged a very imbalanced pack that last time out.
> 
> The Lithium Cells you have are not the issue.


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## Siwastaja (Aug 1, 2012)

I'm not surprised at these problems and would not blame the user. OTOH, the word "user" may be a bit misleading. Although this is "only" DIY, we still have to bear the role of system engineers.

Just _now_ we are starting to get enough data to have a valid foundation on how to select the products and how to use LiFePO4 cells without being rocket scientists, or pioneers.

Just _now_ two BMS products have earned enough reputation and enough actual usage data in the DIY community and have clear enough instructions so that they can be trusted; namely the Elithion system and the MiniBMS. There may be a few more, but not very many of them.

It was quite different when the OP designed his pack or when onegreenev had his negative experiences on one particular BMS (apparently still without a name). No one probably said to the OP; "hey, it's not a BMS at all, it's a top balancer." Still, not everyone here knows what "balancing" means and what it is for, and the same for BMS. It's a slow process of trial and error. This is pretty new technology.


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## onegreenev (May 18, 2012)

Ziggythewiz said:


> Sorry. I should have been more specific. An intelligent person will not blame the user and the manufacturer at the same time. You are free to do whatever you want.


But when you ignore the BMS its totally USER and being that BMS systems always are top balanced systems it is BOTH the user and BMS manufacturer faults. No BMS can stop stupid. 

You are also free to do what ever you want. No one here is a puppet.


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## onegreenev (May 18, 2012)

> or when onegreenev had his negative experiences on one particular BMS (apparently still without a name).


The BMS was built by Hi-Power themselves. Direct from the manufacturer. I only purchased the cells after the original owner encountered the massive failure on many packs using the manufacturers system. How screwed is that. I purchased the cells that survived. I also know what happens with an improper bottom balanced pack and I am not the only one here. Plenty of BMS free systems abound with no issues. 

It's easy to have your controller cut back if you happen to have a smart controller. Same for the charger. Never had and over charged cell except when testing fast charging with a single A123 cell and once my pack was properly bottom balanced I never had an over discharged issue that caused a reversal while driving hundreds of amps through an empty cell. 

If you have a dumb controller and charger you need a BMS. I will not refute that at all. Of the BMS systems I'd rely upon maybe the MiniBMS vs any other. 

It is after all your choice. Again, no one is a puppet. BMS free does work and quite well.


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## onegreenev (May 18, 2012)

> I'm not surprised at these problems and would not blame the user.


I would and the user said he ignored the warning. Too bad. This is the reason for building into your vehicle a way to shut it down so if you happen to be either not paying attention or you just flat out ignore the warning the controller will shut you down. No arguing with the system. Ignore the warning and loose your cells. Have a top balanced pack and drive the pack to the bottom you WILL loose cells.


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## onegreenev (May 18, 2012)

> It is a kludge known to help in a non-BMS system to avoid overdischarge pretty well. What remains unsaid by the proponents, is that bottom balancing moves the lack of protection from the discharge stage into the charge stage.


Well actually its a very simple and very elegant way to avoid disaster when you drive your cells to the end. Its not a matter of if but when. As for moving the problem to the charge end its also very simple. Never charge above the 3.6 volts nominal and keep your cell in the safe zone by limiting the charge. Of course you MUST have a smart charger to do this. A dumb charger can't. If your cells are so out of whack as to allow a charged cell to go beyond 3.8 volts then you need to replace the cell or add in another cell to the whole pack. It is actually a pretty simple exercise. 

Go for a BMS if you must or if you have old chargers and controllers. 

LiFePO4 can't handle overcharging. Period.


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## Siwastaja (Aug 1, 2012)

onegreenev said:


> Well actually its a very simple and very elegant way to avoid disaster when you drive your cells to the end. Its not a matter of if but when. As for moving the problem to the charge end its also very simple. Never charge above the 3.6 volts nominal and keep your cell in the safe zone by limiting the charge. Of course you MUST have a smart charger to do this. A dumb charger can't.


So it seems that you have actually missed the whole issue and are partially succeeding by luck; but it's good to hear it's working for you. 

This explains why you haven't provided any details how to solve the charge side problem, which is the _most important point_ in the critique about your methodology. Nobody's asking you to repeat over and over again that bottom balance together with controller LVC protects against overdischarge. It's quite clear it does exactly just that and works quite well for just that.

When you say "don't charge over 3.6 volts"... What you are missing is: how the heck do you know when the first cells hit 3.6 volts? How does the charger know that? Well, it doesn't!

It's exactly the same issue as with discharging with a top-balanced pack, just in the opposite end. Top-balance, discharge: the motor controller cannot know when the first cells go empty, as it causes only a minor drop in total pack voltage. Bottom balancing may solve this. Fine, they become empty at the same time. But the cells are still of a bit different capacity, and the pack is balanced _at bottom_; when you charge it, the cells become _full_ at different times, causing only very minor rise in total pack voltage, something a charger cannot see, no matter how smart it is (*). While you should stop when the _first_ cell hits 3.6V, you cannot because you don't have cell-level measurement to control the charger.

Now if you understand this, you'll also see how simple the task of the BMS is.

You don't seem to know what a BMS is but are having some large-scale delusions about some mystical "management" of a battery pack, which would be so complex that it would fail due to that, and take cells with it.

A BMS is simply a system that measures every cell voltage and stops both the charger and the load to prevent both overcharge and overdischarge. It could work on any balance point, but top balance just happens to maximize the energy available from the pack. If you wanted to, you could order MiniBMS without top-balancer (shunt) circuit, or remove it, and bottom balance your pack, and in addition to that, have MiniBMS to control the charger.

Now, all that being said, I really believe that a bottom balanced system without any cell-level charger control (known as "BMS") may work, as it seems to work for many people. It would be ridiculous to claim that those people lie about it.

However, it would be better if you did understand _why_ it works and _in which cases_. Here are some of the reasons:

- *LiFePO4 chemistry* is a bit forgiving. Lower nominal voltage, more leeway before instant electrolyte breakdown. A lot more leeway to thermal runaway. Slight overcharging does not instantly compromise the cells.

- *Similar enough cells*. If you have a few cells with significantly lower capacity, they will almost certainly die in the process. This, OTOH, is kind of natural selection. I have read that some bottom-balancers have needed to replace "a few" cells after some time. Their diagnosis is that those "cells are bad", which would be natural for a "cheap Chinese product", and they have accepted that as an explanation. Probably the explanation is just wrong and those cells had nothing bad in them, they just were bit less in capacity.

- *Low enough charging voltage*. Sacrificing a few % of SoC gives a lot of leeway. It also slows down the end of charge.

- *Low enough number of cells*. The fewer cells, the greater effect on total pack voltage from first cells getting full. It works 3 times better with a 100-volt system compared to a 300-volt system.

- *Charge timing*. Stopping the charging when approximately enough time has passed that the battery might be full. This is to minimize the time some cells see overcharging.

The fact that _you _have a working system without considering these things does not mean that anyone can replicate your result just like that. You need to have a little bit more responsibility in giving tips what to do with a $5000-$20000 investment.

If I was to go without a BMS, I would totally top-balance and just be very careful on the discharge side by using an Ah counter and leaving enough leeway there. After all, it's a rare situation that you want to run the battery fully flat, but charging it fully is a daily routine.

(*) Edit: Actually, it might be possible to design a charger that detects one cell getting full from precise pack voltage measurement. It would just be very finicky, probably a lot more than what a NiMH fast charger needs to do.


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## Ziggythewiz (May 16, 2010)

onegreenev said:


> If you have a dumb controller and charger you need a BMS.


Or a decent balance and a competent user (or JLD enforcer).



onegreenev said:


> Its not a matter of if but when. As for moving the problem to the charge end its also very simple. Never charge above the 3.6 volts nominal and keep your cell in the safe zone by limiting the charge.


How is it a matter of when? Don't be careless and WHEN never comes. You're right that you can't stop stupid. It doesn't matter what protections you have in place. Warnings can be ignored (see Tesla) and safeties can be disabled (see Chernobyl).

Just as it's simple to not charge above a certain level it's simple not to discharge past a certain level. In fact, by limiting DOD to 70 or 80% you're never even getting close, but you'll always be charging closer to the limit than that.

It's simple fact that bottom balancing makes you safer on the bottom and top makes you safer on top. Either way you're fine if you stay out of the ends.


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## vmrod (Jul 2, 2010)

i don't plan on ever running to the bottom of my pack. Probably less than 50% daily. 

I will charge it daily, though. Maybe even twice a day, if my workplace doesn't mind me plugging in.

Lithiumate Lite is my BMS. How can I go wrong with this? It will shut me down during any LCV event. (no destroyed cells) I can have it turn on 'valet mode' on my controller during warning events. It will also shutdown the charger during a HCV and report a fault to me for human investigations.

(I will be top balancing my cells.)

Even if I didn't use the BMS for automatic protection, I still would use it for amp hour metering and for individual cell voltage measuring.


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## onegreenev (May 18, 2012)

> It's simple fact that bottom balancing makes you safer on the bottom and top makes you safer on top. Either way you're fine if you stay out of the ends.


Yes. But its safer to keep the bottom balanced over the top because when your nearing the end of charge even with a ragged top your only putting in a few amps and since you will have a lithium charger that can terminate at a specified voltage the few cells in your pack won't die at 3.8 volts and 3 or 4 amps before termination. Where you have the problem is when your charger continues to charge due to the failure of the termination circuit or failure of your BMS and allows your charger to continue to charge at full amperage and over hours and hours of full current after being filled to capacity is when the cells bloat, heat up and burn. With driving and you have a ragged bottom and you drive to where one or more cells reach empty you can and will drive hundreds of amps of current through an empty cell killing it in a matter of seconds vs hours on the other end. 


But, Yes, Stay off the top and bottom and don't be stupid you can very successfully run without a BMS. It actual truth the charger and controller are the BMS on a BMS free system. They just don't keep track of single cells with all that tangle of wires and connections. No need.


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## onegreenev (May 18, 2012)

> This explains why you haven't provided any details how to solve the charge side problem, which is the most important point in the critique about your methodology.......


What? Elcon charger set to 3.65 volts nominal for the pack. It does not take into account that all cells are different and you will have some that show a higher voltage just before you shut down and a few that show around 3.3 volt when ended. But after you let it sit all the cells will be in the 3.35 volt range after your charge. It is fully duplicated and very simple to do. 

I am fully aware of what a BMS is and how they function. I could actually care less if you use one or not. Its your money. I am just giving the option of BMS or not. It is a proven method and has noting to do with LUCK. NOTHING. 

So what is the criteria for you MUST have a BMS?

I quite enjoy not having to muck with all those wires on a BMS.


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## Ziggythewiz (May 16, 2010)

onegreenev said:


> With driving and you have a ragged bottom and you drive to where one or more cells reach empty you can and will drive hundreds of amps of current through an empty cell killing it in a matter of seconds vs hours on the other end.


SO DON'T DO THAT!!

Seriously, most manufacturers recommend 70-80% DOD. There's no reason to regularly do 80% and occasionally do 100%. Shoot for 70 daily, 80 when you need to. Never over 90. It's not difficult.


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## Siwastaja (Aug 1, 2012)

onegreenev said:


> What? Elcon charger set to 3.65 volts nominal for the pack. It does not take into account that all cells are different and you will have some that show a higher voltage just before you shut down


... exactly, and when this "higher" is over 3.65 volts, it's something called "overcharging"... And if you have total of 3.65V per cell over the pack, and you admit some show higher than others, that absolutely MEANS you have cells overcharging there.



> But after you let it sit all the cells will be in the 3.35 volt range after your charge.


Yes -- it is perfectly normal that overcharged cells fall back to same voltage levels as non-overcharged ones, once disconnected from charging.

What you NEED to do is to jump around with a digital multimeter BEFORE the charger stops, and look at the individual voltages while the charger is working. You need to do this for some time, also before the charger drops the current. This way you can attempt to verify whether there is overcharging taking place or not.

I would suggest you start from the basics, even though you have a lot of experience, to get the grasp of basic theoretical concepts. There is a lot of information on EV battery basics online. No offense intended.

Maybe overcharging isn't so bad after all, as you seem to be doing it all the time and being just fine?


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## onegreenev (May 18, 2012)

You can always say don't do it but stupid happens as in this case so saying don't is not part of the equation. It does and will happen again and again.

As for charging you always need higher voltages to charge your cell or battery. At 3.65 I am not overcharging the LiFePO4 Cell. Even at 3.8 volts at a couple amps is not an issue. Many have actually gone to 3.55 volts as the ending voltage but its still higher than 3.35 volts. But under current the 3.8 volts is not over charged. If I let the cell sit for a day and it was at 3.8 volts then I'd say it was WAY over charged. But under current load charging, NO. 

Lots of Lead Acid battery stuff on line. Lots of Lithium stuff that is based on Lead acid and not actual testing too. Many just take that typing smart crap as gospel. Sorry, I don't. 

No offense taken.


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## Ziggythewiz (May 16, 2010)

Siwastaja said:


> Maybe overcharging isn't so bad after all, as you seem to be doing it all the time and being just fine?


OEMs said 4.2V to begin with...then 4, then 3.8 now they're at 3.65. CALB recomends not charging them over 90%. Cell destruction won't happen below 4V but varying levels of degradation occur between 3.4 and 4V


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## PStechPaul (May 1, 2012)

This has become a very informative thread on top vs bottom balancing and the importance (or not) of a BMS. It has taken me a while to understand sufficiently what the problems are with (over)charging and discharging and the destructive effects of cell reversal. I see the relative advantages and drawbacks to top and bottom balanced packs, and the experiences of the OP show the expensive consequences of battery pack mismanagement.

It would probably be helpful to retitle this thread or at least refer to it from one which is more accurately described. IMHO there is no question that LiFePO4 is currently the best technology for a practical DIY EV, although I still think NiMH or even NiCd may have some advantages in cost and survivability when abused. Lead may be appropriate if it can be obtained cheaply enough and used only as a temporary proof of concept and learning exercise to "jump start" an EV conversion.


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## Ziggythewiz (May 16, 2010)

Really we should just have a sticky thread for each Holy War debate where everything can be aired out and referenced.


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## EVfun (Mar 14, 2010)

Ziggythewiz said:


> Really we should just have a sticky thread for each Holy War debate where everything can be aired out and referenced.


That is a good idea. The links to the relevant experiences could be in the thread making user research easy.


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## rmay635703 (Oct 23, 2008)

And 3 years after the op left the thread went on


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## Red Neck (Feb 1, 2013)

If one has good knowledge of his cells, access to controller settings, etc, then top balancing is best, at some 3.8v in parallel, then placing them in series, with a charger set to take them to 3.5v with constant current and then stop.

Then in the controller, you set the car to limit current when at 30% of charge left and to stop before the lowest cells get to 1.5v under load. 

Then you're safe. Cells should also be at same temperature (+-5C), so no
thermal drift occurs and then you have no drift. And you do not need a 
BMS then.

Just an occasional checkup.. It is still good to have a backup for the charger to stop if it malfunctions, either via timer or other means.


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