Understanding Lithium Vs. Lead Acid Help

[nota]

Originally Posted by nota

what is used to measure this resistance a VOM ?
what is a high number or a low one ?

still want to know how to do this measure the resistance ?

[Otdulley]

Going to order a new 2021 Club Car Onword, been pondering lead vs lithium battery thing. Any opinion about this would be appreciated

[Murby]

This thread has raised a few questions about lithium batteries, let me see if I can help answer some of them.

1st question seemed to address the capacity of a lithium battery as compared to the capacity of a lead acid battery.
An amp-hour is an amp-hour no matter where it comes from. With Lead Acid batteries, their life expectancy is greatly affected by their charge/discharge profile. LA batteries do not like being discharged or remaining in a discharged state. The absolute quickest way to destroy a LA battery, besides allow it to dry up, is to allow it to remain in a partially discharged state. The more the discharge and the longer it remains there, the more sulfates build up on the plates and the faster the battery dies.

That said, most deep cycle type LA batteries are rated for around 1500 cycles to a DOD (Depth of Discharge) of around 30%. That means you only get to use 30 amp-hours from a 100 amp-hour battery. If you take it down to 50% DOD, you might only get 500-700 cycles. This assumes you discharge the battery and immediately charge it back up right away.. Allowing the battery to sit for hours or days will further degrade its life expectancy.
Some LA batteries can not even reach 1500 cycles, some, like Trojans, can go even higher.

LA batteries can lose more than 1/2 of their capacity at temperatures below 40 degrees, and at freezing temperatures, they can lose even more. LA batteries perform best when they are warm, but the heat also shortens their life.

Lithium batteries do not mind being left in a partially discharged state, in fact, they love it. If you want to make a lithium battery last a long time in storage, store it at just above freezing at about 30% of its rated charge voltage, and it will probably still be good when you're 6 feet under.

Lithium batteries degrade because of undesirable parasitic reactions (PR's). PR's are always happening within a lithium battery, the question is "at what rate are they happening?".
PR's increase at high voltages, meaning that if you have a lithium cell that is rated for 3 volts to 4.2 volts, then the PR rate increases when you give the battery a full charge to 4.2 volts. I should note here that I'm talking about Lithium Polymer(ion) type batteries and not the Lithium Iron Phos cells. The LiFePo4 cells run under much the same rules, but their voltage ranges are different, so make sure you keep that in mind.

With most lithium ion batteries, you want to keep your charge/discharge profile between 3.4 and 4.05 to 4.1 volts. You will lose 8% at the bottom, and another 8%-10% capacity at the top, but you will quadruple the cycle life of the cells.

PR's increase in lithium ion batteries proportional to temperature. The cooler they stay, the longer they last.
PR's increase in lithium ion batteries in respect to the cell voltage as well. In general, never charge them all the way up. This applies to your cell phone, flashlight, and your EV passenger car. (although the car has a computer programed to show you 100% when before the cells reach 4.2 volts)

All lithium batteries have a C rating. C stands for the capacity of the battery at one hour. So if you have a 100aH battery and you discharge it at 1C, then you've discharged the entire battery in an hour. That same battery at 2C means you've discharged the entire thing in 30 minutes.. and at C/2, it means you discharged it in 2 hours.

Chevy Volt cells can discharge at around 7C to 10C.. They are absolutely amazing batteries. My original off-grid system used a Chevy Volt pack. The problem is that they are only a 12s configuration so they are fully charged at only around (4.1v x 12s) = 49.2 volts. As your voltage drops, your load has to draw more amps to do the same job. For off-grid inverters, this can be an issue.. I'm not sure (yet) how golf cart control circuitry would behave.

If you decide to build your own custom lithium (any) battery, make absolutely sure you get a high quality BMS. Stay the hell away from anything made in China. REC BMS, Orion, Batrium, etc.. are all good units.. and they are priced accordingly. Expect to pay $800 or more for a good BMS that won't allow your expensive batteries to catch fire.


Internal Resistance: You can not measure the internal resistance of a lithium cell with a multi meter. The internal resistance is a calculated measurement that is made after and during charge cycles. The internal resistance on high quality EV cells is usually in the 0.1 ohm range.. the test leads on a multi-meter have more resistance than that.

You won't know what the internal resistance of your cells are until you hook up a BMS and charge them.

Buying used lithium ion batteries is always a gamble.. although not a big gamble. The best test you can do to them is a straight forward capacity test. Problem with that is it usually takes some specialized equipment to perform that test on large packs. Its not like you can hit the power switch and see how long the light bulb stays on. You need a calibrated load and a monitoring system. Best to use common sense and purchase from a reputable dealer or something who is trustworthy.

Lithium is far superior to lead acid in almost every way imaginable.. LA wins in the safety department however. But properly designed, lithium batteries are safe..

I hope that helps,

[DaveTM]

Originally Posted by Murby

...If you decide to build your own custom lithium (any) battery, make absolutely sure you get a high quality BMS. Stay the hell away from anything made in China. REC BMS, Orion, Batrium, etc.. are all good units.. and they are priced accordingly. Expect to pay $800 or more for a good BMS that won't allow your expensive batteries to catch fire. ...

Your post is a great source of information. I will point out though (always a "but ) that a ZEVA BMS is a good unit and cost me $490. Not near the $800 you have stated above.

Just an FYI!!

[Murby]

Originally Posted by DaveTM

Your post is a great source of information. I will point out though (always a "but ) that a ZEVA BMS is a good unit and cost me $490. Not near the $800 you have stated above.

Just an FYI!!

The problem with the ZEVA BMS is that it only has 80ma of balance current. That's fine for small e-bike batteries and things of that nature, but if you hook that up to a large pack, or a pack that requires a lot of balancing, its going to be like trying to drain an Olympic sized swimming pool with a drinking straw.

In fact, that's one of the biggest problems with a lot of these BMS's.. their balance current is so small its basically useless for larger packs.

Take a 100ah pack of Chevy Volt batteries and the ZEVA would probably work fine.. but that's only because Chevy Volt batteries are of such high quality that they almost don't even need a balancing function. I've seen people on youtube claiming they've run the Volt batteries for over a year without a BMS.(I don't recommend that)

Try that with a Nissan Leaf battery and I don't think that ZEVA would keep up.
From my own experience, and from listening to the experiences of others, you need a balancing ratio of around 0.001 to 0.002 to the size of the pack in amp hours.

So a 100aH pack x 0.001 = 100ma of balance current at an absolute minimum. And if the batteries are of a lower quality, then its 100ah x 0.002 =200ma of balance current per 100aH of capacity.

One other note to be fair about this: I think it also makes a difference on how frequently your battery bank is used. In a solar application like mine, the battery gets used 24/7 when the grid goes down.. with a golf cart, that's not the case unless your cart happens to be used for work purposes or you go riding every day.

A battery bank that does some work and is then charged and left to sit for days or even weeks, would allow time for a BMS with a small balancing current to do its job. With that in mind, if your 100ah golf cart battery is being used for occasional recreation purposes, and if you leave the BMS connected at all times, you could probably get away with the small balancing current.

[Sergio]

Why do You think that balancing is needed that often?

There are quite a lot of folks here that have built their own lithium packs like myself and "keeping the cells balanced" is not an issue.

If using a BMS the only practical solution is a "Top Balance" which means if the cells differ in capacity or age they may/will show a larger delta near the bottom but that is not an issue as they will return to the same "balanced" level when charged.

The Volt packs are not very economical if you need to parallel more than one due to the cost of additional BMSs and properly combined LV and HV cutoff systems.

[Murby]

Originally Posted by Sergio

Why do You think that balancing is needed that often?

There are quite a lot of folks here that have built their own lithium packs like myself and "keeping the cells balanced" is not an issue.

If using a BMS the only practical solution is a "Top Balance" which means if the cells differ in capacity or age they may/will show a larger delta near the bottom but that is not an issue as they will return to the same "balanced" level when charged.

The Volt packs are not very economical if you need to parallel more than one due to the cost of additional BMSs and properly combined LV and HV cutoff systems.

I think everyone has their own methods to running lithium cells. I like to make sure mine are balanced to within 10mv of each other.

You can use a single BMS on multiple Chevy Volt packs if you tie all the cells together from each pack. I didn't do it myself because the way I had my bank set up, I used the factory BMS connector which made it easy to plug the BMS into each of the packs occasionally. That, and the fact that they mostly stayed balanced all on their own.

But if you have an older Volt pack, you can run a 14 gauge wire and connect all Cell 1 tabs, Cell 2 tabs, Cell 3 tabs, etc. Just use a fuse on the wire for safety. The BMS will see the individual cell numbers as a single unit.

The more a pack is unbalanced, the more capacity the pack loses until all cells are balanced.
A large pack that is out just 300mv could lose 5kw of capacity until those cells are balanced. But I don't think most folks with most packs run into anything like that.

[Sergio]

If You search the site You will find out that everyone's pack here is pretty much balanced within 0.01v when charged.

The only time I see folks get erroneously concerned with balancing is when they check the cells voltage near the bottom of the SOC and interpret any difference in voltages as an indication of "imbalance", which is not.

If you search the site You will find many different implementations of DIY packs that are fully automated so you don't need to move any cables around.

[DaveTM]

Originally Posted by Murby

Try that with a Nissan Leaf battery and I don't think that ZEVA would keep up.

I've been running a 14 module Leaf pack on my cart for sometime. (Prior to the 14 module pack, I ran a 7 module pack for about two years). My ZEVA unit has yet to "bark" about anything. However, I have the settings set to the proper parameters and the cells were all in balance when installed.

Like this:

The Zeva has been more than adequate to keep in check and balance my Leaf pack. I don't know where you get your information about the ZEVA, but perhaps double checking your source may be in order.

[Murby]

Originally Posted by DaveTM

I've been running a 14 module Leaf pack on my cart for sometime. (Prior to the 14 module pack, I ran a 7 module pack for about two years). My ZEVA unit has yet to "bark" about anything. However, I have the settings set to the proper parameters and the cells were all in balance when installed.

Like this:

The Zeva has been more than adequate to keep in check and balance my Leaf pack. I don't know where you get your information about the ZEVA, but perhaps double checking your source may be in order.

What is the amp-hour capacity of your leaf pack?