Max current draw issue?

If you hook two with bms in parallel, that's fine.

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I have 2 identical 72v 11.6Ah luna battery packs, each one has a BMS with 50A continuous 70A peak.

I could only ever draw 55A max out of a single pack.

I have both packs hooked together in parallel, but still only drawing 55A max. Controller is Lyen Mark II rated to pull 65Amps. I'm trying to figure out if the BMS can limit total power output, because I was under the belief that I should be able to get 100A (140A peak) from this setup. Am I missing something, or do I need to check out the controller settings? Was going to upgrade the controller next anyway, but not if the BMS is going to keep total current draw to 55A.

Thanks!

This thread seems young and alive so I might find some help here!:

I have 2 identical 72v 11.6Ah luna battery packs, each one has a BMS with 50A continuous 70A peak.

I could only ever draw 55A max out of a single pack.

I have both packs hooked together in parallel, but still only drawing 55A max (voltage sag is less now). Controller is Lyen Mark II rated to pull 65Amps. I'm trying to figure out if the BMS can limit total power output, because I was under the belief that I should be able to get 100A (140A peak) from this setup. Am I missing something? or do I need to check out the controller settings? Was going to upgrade the controller next anyway, but not if the BMS is going to keep total current draw to ~55A.

Thanks!

xnoitulos said:

Controller is Lyen Mark II rated to pull 65Amps.
<snip>
I should be able to get 100A (140A peak) from this setup.

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No;, see bolded part of your statement. If the controller can only safely pull 65A then that's what it can pull. If you can program it or modify the shunt (lots of threads about each of those) then you can pull more current, but if the controller can't safely handle it it may just blow up.

It also depends on whether or not what you are doing with the system will even cause it to pull that much current--just because it's available doesnt' mean the system will use it.

But really your question doesn't have anything to do with the topic at hand; I'd recommend letting me move this to it's own thread.

No;, see bolded part of your statement. If the controller can only safely pull 65A then that's what it can pull. If you can program it or modify the shunt (lots of threads about each of those) then you can pull more current, but if the controller can't safely handle it it may just blow up.

It also depends on whether or not what you are doing with the system will even cause it to pull that much current--just because it's available doesnt' mean the system will use it.

But really your question doesn't have anything to do with the topic at hand; I'd recommend letting me move this to it's own thread.

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Please, take it where it needs to go! :wink:
I'm only looking to make the controller pull 65A. On my stock GNG gen2 kit, I use the same luna 50A BMS, but the controller will only pull the 20A its rated for. I was under the impression that these 2 packs in parallel would be capable of 100A, allowing the controller to reach it's full rating of just 65A, and going easier on each pack as each would see ~33A draw?
I'm climbing some big hills and taking hard pulls from standstill (testing everything! ) What's suspect to me is that the peak amp draw is the same as a single pack. I guess my question is can the BMSs "see" each other or some other way it's keeping the limit at ~50A with 2 packs together in parallel? Or should I be looking at the controller for the limit/bottle neck?

Thank you

I split it off to it's own thread; you can edit the title of it if desired by editing the first post in the thread.


Regarding the problem, if it is teh same current draw but with less sag using two packs vs one, then it means your limitation is either in the controller itself, or it is simply that your system isn't even trying to draw more than that, becuase it isn't being pushed hard enough to do so.

It could also be that whatever you're using to measure the current is inaccurately reading it.

IMO, what is really going on here, is your ass is not fat enough to MAKE your bikes draw the max amps.

Get what I mean? You have so much power, and are light enough, you will never see the full potential of your controller, you get going too fast on less. It's NOT a problem. IMO, it's what you aim for in a build. Even bigger motor, or just overload it till it's squealing for mercy, then you will pull that 65 amps. But if it's not screaming for mercy, it might last a lot longer in daily use.

I'm having a hard time believing my ass size is the problem here. Using a CA3 for measurements.

Can anybody confirm that two batteries, each with their own BMS, can be hooked up in parallel and have their max amperage doubled?
If I go and get a 100 amp controller, is it still going to peak at 55A because that's all my ass needs to get moving?

dogman dan said:

IMO, what is really going on here, is your ass is not fat enough to MAKE your bikes draw the max amps.

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xnoitulos said:

I'm having a hard time believing my ass size is the problem here.

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This made me laugh so loud I nearly spilled my drink over my laptop….

Parallel won’t give more amps Series will give more amps as series makes your watts bigger so you have a bigger battery more speed more amps. if your controller can take more amps then you will be limited to your controller amps period. Parallel will give you more range (distance).

If you need to pull 65amps you need a controller that will do that. But if your battery is rated lower amps you will have less life and eventually ruin the battery cells due to pulling (forcing) higher amps/ watts.

Perhaps I am wrong, but I thought a BMS only monitors voltages. It doesn't measure current, so it should let the battery pump amps until the series voltage on a parallel cell combo gets too close to the individual 18620 LVC or sags down to that level. Meanwhile, it also watches the overall battery LVC and kills the battery if that is reached. With two batteries in parallel, nothing changes.

The peak battery current is a design number obtained from how many batteries are in parallel, and their safe power output.

Maybe they were overly optimistic about the controller rating, but you probably just don't need more than 55 amps to do what you are doing. Got a trailer and a big dog? Try towing that up the hill.

Parallel won’t give more amps Series will give more amps as series makes your watts bigger so you have a bigger battery more speed more amps. if your controller can take more amps then you will be limited to your controller amps period. Parallel will give you more range (distance).

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Perhaps there's something specific to this setup that somehow alters this (though I doubt it), but normally parallel does indeed give you more amps. Look at any battery pack and you'll see that the total continuous current rating is the same as an individual cell's continuous current ability multiplied by the number of parallel segments (unless/until limited by something like a BMS). Adding power sources in parallel does increase capacity (amp-hours) as well as instantaneous flow (amps), it is true.

The situation would be no different with two packs in parallel (assuming fairly matched resistance, etc.) -- each will provide half the amps you draw. From the perspective of each BMS, they should only see that they are sourcing x amps out of the 2x you're drawing, so you should as you surmised be able to provide twice the current from those two in parallel compared to one alone. I think the others are probably correct in suggesting that your motor at full throttle up a hill simply doesn't pull any more current from those two batteries than what you're seeing.

But hey, your batteries will last twice as long this way.

Ok, let me rephrase that comment.

I think part of the problem is you are too light. You get going so fast, there is not enough load on the motor to reach its potential maximum. Yer flying on 50 amps.

Get it? Your power to weight ratio is too good to have the motor even try to pull it's hardest. That's how electric motors work. It won't pull any harder than it needs to.

The rest of the problem is going to have to do with other shit, including watt meter calibration. It could be some resistance in the wires, connectors, etc. It could be that the controller is in fact programmed for less amps than you thought, any number of other things.

One easy test would be to put more load, more weight on the bike. See what happens. If you don't see more amps, then it's a real something else limiting it.

Or could ride with brakes on and max throttle for a short while. Hopefully doesn't burn up controller and motor.

A 70A peak capable BMS won't interfere with current until beyond that value, and when it does, it will trip off. It has no way to "limit" current other than to zero, like a switch or circuit breaker.

The controller makes a voltage down-conversion depending on the throttle position. The motor resistance, back EMF and wiring resistance determine the current that flows. Make sure all the wires are short and adequately heavy, and the connectors are high current capable good connectors, on both the battery to controller and controller to motor. The motor current will be at least several times the battery current at low speeds. Ebike wiring is often a bit light for the current it carries, but if it is too light it will reduce current flow and get hot, possibly even fail.

There are a couple of settings in the controller that limit the current, one is the obvious battery current limit, the other is the phase current limit or multiplication factor. If it is set too low it will override the battery current limit at low speed. It needs to be set to a safe current for the motor and wiring.

Generally a controller will only hit max current somewhere in the midrange of speed, it won't be as high either at the start or at the high speed level.