What to I misunderstand about batteries?

[hodgie]

I understand that:

Batteries can come with a BMS attached or not.
Most batteries sold in kits that have a basic power supply AC to DC have a BMS inside the case, with the battery.
Some shrink-wrapped packs, like Ping, have a BMS included, usually - I assume they only require a power supply to charge.
You can buy a BMS to add to a shrink wrap battery.
Or, you can buy a shrink wrap (Zippy) that has no BMS and use an external iCharger i.e. to charge and balance the batteries.

Have I got this totally messed up?

[gensem]

Only RC lipo does not usually have a BMS all the others shrink wrapped batteries do have.

[ZOMGVTEK]

The BMS isn't really just for charging. BMS is a term thats often used very loosely. Many BMS's are very poor. The fact that it has a BMS does not mean its a perfect system that can be used or abused like a lead acid battery. A BMS should cut charge power when all the cells are full, disconnect the battery from the load when any cell gets too low, and keep cells in balance. You can charge basically any battery with a power supply. Most Lithium batteries tend to be EXTREMELY easy to charge. You just need to know the cell voltage, and thats about it. PB/NiMh/NiCd all have more complex charging schemes to achieve peak performance. The only issue, is you need to know EVERY cell voltage. If you have a high voltage pack, with 24 cells in series, this means you need to monitor 24 cells. A BMS can do this for you, or you can do it yourself. You can buy a BMS and install it on any pack, or buy a pack with one in it already. It just depends on your goals. For high power, most pre-made packs tend to be poorly suited. The RC LiPo (Turnigy/Zippy/etc) tends to be well suited to this, but fairly dangerous when used improperly. You can get packs pre-made out of 18650 cells that are 'safe', but won't dump tons of power, and often charge slow.

You don't NEED a BMS to charge or discharge any battery. It's just a good idea, especially for an inexperienced user. I don't think batteries generally have a charger built into the BMS/case.

[dogman]

Actually, a bms equipped battery like a ping prefers to be charged with a lithium charger. Why? because it shuts off when it's supposed to.

In the case of the ping, the charger puts out a set voltage. The bms monitors the voltage of each set of paralelled cells. When the battery gets close to fully charged, the charger shuts off. At that point, the bms is already letting some charge out of the highest charged cells. After awhile, the bms discharges the high cells far enough, and the charger starts up again. This is repeated till the battery is fully charged and balanced. A very out of balance pack may need days and even weeks on the charger to fully balance. But normaly, the pack charges fine and needs no balancing at all.

You can charge a bms equipped battery with a power supply, but you might want to set it to undercharge just a bit. Otherwise, the PS will just chug along till you have overcharged some of the cells in the pack. The bms will still let some charge out of the high cells, but it won't be able to keep up unless the PS shuts off, like the charger does automaticly.

The ping bms also works while discharging, shutting off the entire pack if one group of cells is discharged.

[hodgie]

Thanks alot for taking the time to explain all that.

So, a Zippy pack can be charged with a charger and balanced every so often but that is still not as sure as having a BMS on board that is constantly assessing the state of charge/discharge for the individual cells?

Do people who use shrink wrap packs have their own quality BMS that they attach to the pack (even replacing an OEM BMS if they think it is crap)?

How do people typically set up their packs? What do they do/attach to charge them? Are diodes a good idea for parallel packs to avoid undesirable current flows between batteries?

If you are a "casual" user, is it just safer to use a pack with a BMS like Ping or just stick with a low-performance idiot-proof battery unit (rack mounted or bottle battery)?

Thanks in advance for kind responses.

[dogman]

With lipo, you are naked. So the bms, such as it is, is generally you. So you need to do something to be sure you don't overdischarge.

There are HVC- LVC boards you can buy. Then you have a lipo bms. viewtopic.php?f=31&t=36414

And there are various ways to monitor packs. I always recomend new lipo buyers to get a cellog 8. A very handy device for checking packs individual cell voltages quickly. Some buy several, and they become part of the bike.

Others may just monitor the entire packs voltage. This is what I do, combined with not riding farther than the theoretical range of the pack. I use a Cycleanalyst, and running a 10 ah pack, try to be back home on 7-8 ah.

You can use a speedo, or just a set distance you know you can make. Say you work 5 miles from home, and have a pack you know can go 15 miles. Not much to worry about then, riding 10 miles to work and back.

And there are low voltage warning devices. I use them when I am going on long rides, and want to completely discharge one pack, then switch to another.

[hodgie]

Thanks for comments.

Why don't you just run those battery packs in parallel? Would that reduce stress on the packs?

[Ykick]

Thanks for comments.

Why don't you just run those battery packs in parallel? Would that reduce stress on the packs?

We do and it does.

DM's talking about 10Ah which is 2P (parallel) 5Ah bricks. I usually only need 10Ah but in winter I double to 4P (20Ah) in order to keep stress and cold weather sag to a minimum. Sometime, I run a 3P (15Ah) pack to help with any detours from my normal commute.

Although I may say 10Ah, in practice I try not to ask more than 7Ah from that configuration and rarely charge to 4.2V/cell. This also helps reduce stress on RC Lipo bricks.

[hodgie]

Understand. Can a person use too high of a "C" rating...causing the controller to crash? Do controllers limit the current?

[Ykick]

No such thing as too high C rating. Nothing to worry about there.

[Joe Perez]

Understand. Can a person use too high of a "C" rating...causing the controller to crash? Do controllers limit the current?

They say that you can't be too rich or too thin.

You also can't have a battery with too high of an Ah rating or too high of a maximum discharge C rating.

The battery's Ah and C ratings are only a measure of how much current they are capable of delivering without being damaged or experiencing excessive voltage sag, but the actual current which is drawn from the battery is entirely dependent on the controller. The only specification on a battery which can be "too high" for a given controller is the voltage.

It's possible for the controller to draw more current than the battery or BMS are capable of handling. It is not, however, possible to have "too high" of a current rating on the battery or BMS relative to the controller. So long as you had a sturdy trailer to haul it around on, you could build a 1,000 Ah battery with a 50c discharge rating, and it would work just fine on a 20A controller.

[hodgie]

@Perez: Great explanation. That clears up alot for me.

I read that the "C" rating is often grossly overstated....by as much a 50%.

If I have a 36V geared motor on my EVG bike with a 50A max controller that typically pulls 5-15A continuous and 35A burst, I am assuming a quoted "C"rating of 25 would be more than enough. But, I also have read that the higher the "C" rating, the more resillient and long lasting a battery can be.

So, I am thinking of startng with 5S2S (25-35C) LiPo batteries that I run in parallel with another battery (using diodes to keep the batteries friendly). I don't really like being a human BMS. But, say, a LiFePo4 battery pack with BMS is terribly expensive for a starter like me.

[hodgie]

I am a cautious guy. And, the dangers of charging a LiPo are of concern - it seems a little like trying to create rocket fuel in a basement lab.

Also, I REALLY like rolling my bike up to my outside outlet and just plugging in a wire or two and walking away until the next time I need to run an errand (I have an SLA in the battery compartment and bottle battery outside on my EVG bike right now). Of course, the SLA sucks but it provides enough extra current to give me that extra boost that my wimpy, low "C" bottle battery does not have.

Sure like the plug and play aspect of my setup right now. But, I have two EVG battery boxes. So, I could trade out used for fresh fairly easily.

[Joe Perez]

Also, I REALLY like rolling my bike up to my outside outlet and just plugging in a wire or two and walking away

That's really what pushed me towards Cell_Man's LiFe battery- simplicity. Come home, plug in one cable, and walk away. No need to fuss with a half-dozen different charging and balancing and charging leads, or to maintain a regular regimen of externally balancing all the cells once a week (or whatever it is the LiPo crowd does).

And, to be honest, I found that once I added up the costs of not just the LiPo packs themselves, but all of the charging / balancing / BMS hardware to go along with them, the final cost wasn't all that far off of a turnkey LiFe solution of equivalent capacity which should deliver roughly double the number of discharge cycles.

LiPo certainly has its place among those running motors with penis-shaped vent holes cut in them who can actually take advantage of 30c discharge rates, but for a commuter bike, LiPo no longer makes sense.

[dnmun]

trying to go cheap on a battery pack ends up costing way more in the long term. if you are naive about battery packs, then just buy a ping pack. and buy at least a 48V pack so you can use the full capacity with the 36V controller like i recommended on the other thread you started on this.

lipo packs can and do cause fires, especially if you do not use the full HVC charging protection like methods sells.

lifepo4 do not cause fires.

your current battery is limno4, cheap but not capable of producing the current you think you need. but if i recall, you still do not know if it is the current or weak cell that shuts down your little baby bottle battery.

[Ykick]

RC Lipo makes sense to me because I can replace 20Ah high rate cells for under $500. I can charge those cells in minutes instead of hours and they're smaller and lighter than LifePo4 alternatives. Sure, I had to source some equipment but it's great equipment to have and serves as my tuition to EV battery school.

When I get in from riding, I unplug the battery/controller plug in the charge lead, note the pack voltage and if that looks good, power up the supply and walk away. Minutes later it's full, but I won't leave any high current power supply source unattended for very long. That's asking for trouble no matter what chemistry you wanna fool yourself about being safe.

RC Lipo ain't for everybody and if you don't get it, stay away from it. If you do get it, it can be a great deal $/Wh.

[hodgie]

Thanks for all the comments. Widens my perspective on the pros and cons.

[cal3thousand]

RC Lipo makes sense to me because I can replace 20Ah high rate cells for under $500. I can charge those cells in minutes instead of hours and they're smaller and lighter than LifePo4 alternatives. Sure, I had to source some equipment but it's great equipment to have and serves as my tuition to EV battery school.

When I get in from riding, I unplug the battery/controller plug in the charge lead, note the pack voltage and if that looks good, power up the supply and walk away. Minutes later it's full, but I won't leave any high current power supply source unattended for very long. That's asking for trouble no matter what chemistry you wanna fool yourself about being safe.

RC Lipo ain't for everybody and if you don't get it, stay away from it. If you do get it, it can be a great deal $/Wh.

How many minutes are we talking?

30?

[Ykick]

How many minutes are we talking?

30?

10A charger - 30-40 is my average trip. Very rarely over 60.