37v 10s2p vs 37v 10s4p

[JMK1000]

Hi Group,

Thank you for accepting me to the group. I have a question (probably layman question) about the battery for a scooter I have.
It is a scooter with a 250W brushless hub motor in a front wheel and a 5.8Ah 37v battery in configuration 10s2p.
Since the distance on single charge is really not very impressive (about 5 miles), I want to add an external battery with a switch, allowing me to switch to an external battery when the main one is exhausted (or rather start with the external and when it's gone switch to the internal.
I would like to use, as an external, a battery with more capacity, so I thought about 10s4p. As I understand, comparing with the 10s2p, the 4p has less voltage drop, with the same system attached.
My question is about the dangers: it can draw twice as much amperage if the attached system requires that, so is it risky to attach it to the system which originally had 10s2p? The battery was limiting the output. Or it should not matter. My scooter is Megawheels S5, but this is not important since there are plenty of scooters in that configuration.
I would appreciate if anybody could address such a trivial question of a 'newby'. Thanks. Jack

 

[amberwolf]

My question is about the dangers: it can draw twice as much amperage if the attached system requires that, so is it risky to attach it to the system which originally had 10s2p? The battery was limiting the output.

the controller should be what's limiting the output, so nothing should change from having a larger capacity battery. (it might sag less in voltage, and so have better response to hard acceleration, or hill climbing, to some degree, but not usually very much).

if your controller does not do current limiting (unusual) then the battery voltage sag would indeed be what is limiting power, so one that sags less would limit less. how much that affects your system, heat-wise, you'd have to find out experimentally.


when you do add the external pack, i recommend wiring it in parallel with the output of the internal pack, rather than switching it, as that is easier on both packs. if that's not an option, switching between them works fine, but you must use a switch that is rated for the dc voltage and current that will pass thru it, so it might be on the larger side.

just disconnect them when charging (so charge current can't bypass the bms input and overcharge a cell via the output if the bms of one shuts off it's input).

 

[JMK1000]

Amberwolf, thank you so much for the answer.
This was my understanding.

I will install the switch. The one I chose is rated for 15A on 120V. So it should be OK, I guess. And I will be switching when stationary, so arch is not a problem. It will give me better control of the power at my disposal.

Cheers,
JMK

 

[JMK1000]

Amberwolf, another question, since you suggested a parallel connection.

One of the batteries is 10s2p with it's own BMS, and the other is 10s4p with it's own BMS. Isn't it true, that when you connect the different capacity of the batteries together (in Parallel) they do not discharge evenly? How is it in reality? I want to use both batteries to their full capacity. The whole purpose of this exercise is to extend the range of the scooter, as much as possible.

Cheers, JMK

 

[amberwolf]

The one I chose is rated for 15A on 120V.

is that 120vac or 120vdc?

if it's designed for ac, i wouldn't recommend switching dc with it.

 

[amberwolf]

One of the batteries is 10s2p with it's own BMS, and the other is 10s4p with it's own BMS. Isn't it true, that when you connect the different capacity of the batteries together (in Parallel) they do not discharge evenly? How is it in reality?

they'll discharge based on their internal resistance. if they're paralleled, they'll always be at the same voltage, so if one of them sags a lot internally due to high internal resistance, then the other one will supply more of the current.

basically since the current draw is divided between the packs when paralleled, the load on each one is less, so the packs are not pushed as hard, and they get both a longer lifespan, and at least a small amount more of usable capacity than if they were used separately. (it might be such a little amount it's irrelevant to your needs, but it might be enough to give you noticeably more range than you had with each one independently, used one after the other).

when the first one (whichever that is) reaches it's low voltage cutoff, it's bms will disconnect the output, and the other pack will then take over the whole load, until it's bms does the same.

but the controller should have it's own lvc that shuts off the controlelr before either bms does that (because running a battery down to it's own lvc, every time you use it, is hard on the battery. typically the bms is meant to be an emergency shutoff, not the every day shutoff, and the controller lvc will be a bit higher so it's not as hard on the battery) (there are more advanced bmses that allow the lvc to be set higher, to do this kind of thing at the bms itself, but the cheap ones are usually at the lower point).


either way, there shouldn't be a problem, as long as the only connection paralleled during discharge is the discharge port, and the only connection paralleled during charge is the charge port.

 

[JMK1000]

Thank you very much.
I will use them separately. Taking under consideration, that the external battery is a cheap battery (with a unpronounceable name), and the internal claims to be LG, but who knows... it's more prudent.

Now the only thing left is wait for a shipment from China, make an external housing (aluminum, rectangular tube), and run additional leads to and from the switch.
Thanks again.
Cheers,
JMK

 

[JMK1000]

Amberwolf, thanks for the advice so far. I hope that you are staying safe.

You recommended using the booth pack in parallel simultaneously.

I finally got the 10s4p 37V battery. Since I disassembled the whole scooter, I know that the controller limits the current to 12A.
So far I use the packs separately ( I have 10s2p - 5.8 pack and 10s4p - supposedly 14 pack). To my surprise, the range increase is minimal, but acceleration and climbing, say 25% better.

Since you recommended using them in parallel - what would be the effect of it. How would it affect the range (the climbing might be a bit better if the scooter doesn't already drop 12A from the bigger battery).

Can you speculate on that? The original 10s2p is LG (supposedly), and the 10s4p is some 3rd (or 300th) party (haha).
Thanks in advance for your advice.
Jack

 

[amberwolf]

So far I use the packs separately ( I have 10s2p - 5.8 pack and 10s4p - supposedly 14 pack). To my surprise, the range increase is minimal, but acceleration and climbing, say 25% better.

If you don't get much range increase, then either the scooter is using a lot more power a lot of the time because of less voltage drop, or the new pack isn't anywhere near the capacity it says it is (or is really crappy cells, and/or is severely imbalanced).

The original 10s2p is LG (supposedly), and the 10s4p is some 3rd (or 300th) party (haha).

Well, 6A per cell, for a 2p pack at 12A, could be some serious voltage sag if the cells can't handle it well (due to type of cell, or aging, or both). So adding more cells decreases the voltage sag, increasing the actual power output (v x a) capability of the system.

If the unknown cells in the new pack are as good as the original pack's cells, you should be seeing almost three times the range you had before, because you would have three times the capacity.

Since you're not, that means either

the new cells are very crappy, which you can't do anything about other than replace the pack,

or

they are very unbalanced and so it can't deliver the full capacity due to the non-full cells in there. They have to be *very* unbalanced, because if you are only seeing a few percent (?) range increase, some of the cells in there must be nearly empty even when the rest of the pack is full, so that pack cuts out pretty early in a ride. That you can fix, at least temporarily, by leaving the pack on the charger for a long time (probably days or even weeks if it's that bad), and as long as the BMS is a balancing type, it will fix the problem over time. The longer you leave it on the charger, and the more often you do that, the better it's balance will become, but if the cells are crappy or there are problems with the pack (build quality, cell quality, etc) then this is only temporary each time, and would have to be redone after every ride.

 

[JMK1000]

The new battery is crappy, that's beyond the question. I opened it up, and checked the groups. Now all of the 4 cell groups have the very similar (almost identical) voltage when charged and after the run (of course I can't check the individual batteries, but when all parallel (4 batteries) groups behave the same, I do not have the problem with the stability of the system.

My old (small) battery 10s2p charges to 42.1V and then cuts off when 34.6V, whereas my 'crappy' new battery charges to 42.2V and cuts off when 36.6V. I believe this is regulated by the inside circuits. This definitely has the impact on the range. But the climbing and accelerating is better.

So, would it be beneficial using them together i parallel? At this point they are both outside. I can change it easier, and shut off completely. I control the temperature of the batteries when run up-hill, or as fast as it goes for a while. Also while charging. So far they do not heat up. Again, it's probably because of the limiting electronics.

What would be your take on it?

 

[amberwolf]

The new battery is crappy, that's beyond the question. I opened it up, and checked the groups. Now all of the 4 cell groups have the very similar (almost identical) voltage when charged and after the run (of course I can't check the individual batteries, but when all parallel (4 batteries) groups behave the same, I do not have the problem with the stability of the system.

You might be misunderstanding how the battery is wired, or what to check. There will be 10 (ten) groups (each with four cells that you cannot check individual voltages of) that must be checked. Each one of these 10 should be about 4.2v full, and about 3v minimum when empty, but usually closer to 3.3-3.5v.

You will want to check at least two different things, in either order.

When the charger shuts off the first time during a charge, check the 10 (ten) different group voltages. All should be about 4.2v. If they are not, then any that are different have a problem. Post all of the votlages, starting from the most negative, going up to the most positive, here in teh thread, and we can then help you figure out which of them have what problem.

When using just that battery on the scooter, and it shuts off from being empty, check the 10 (ten) different group voltages. All should be the same, and at something around 3v, or around 3.3v, or around 3.5v, etc. If they are not all the same, then any that are different have a problem. Post all of the voltages, starting from the most negative, going up to the most positive, here in teh thread, and we can then help you figure out which of them have what problem.

My old (small) battery 10s2p charges to 42.1V and then cuts off when 34.6V, whereas my 'crappy' new battery charges to 42.2V and cuts off when 36.6V. I believe this is regulated by the inside circuits.

They may cut off at different voltages because of the BMS, but it's more likely that they do this because of imbalance between the cells. (the first one to run out shuts off the whole pack).

So, would it be beneficial using them together i parallel?

It's unlikely to make much difference to the range, but because of less lost energy in voltage sag, it would make some (you might not notice the difference).

Since you are getting the same range even though you now theoretically have about three times the amount of capacity ("6p" vs 2p, even if 4p and 2p are not used at the same time), the new pack must only last you a very very short time to not add any range to the system with the old pack. That won't change if it's paralleled, until you fix whatever is wrong with the pack that causes such an extremely low capacity.


it would mostly make a difference to the acceleration and whatnot, because of less voltage sag more power reaches the motor and less is wasted in the batteries.

However, you said you are already getting this on both batteries (from whatever you've changed in the scooter (connnections, etc?)) even though you are using the batteries separately, rather than in parallel.

 

[JMK1000]

Answering to your questions:
1."Each one of these 10 should be about 4.2v full, and about 3v minimum when empty, but usually closer to 3.3-3.5v. "
Each is 4.1V full and it goes to 3.56V when shot off - in my newer 10s4p battery. This is my point what I was rising it doesn't go down to the same voltage as my 10s2p which is going much lower.

The whole battery, and all goups do go to 41.2-4V, not above. I tried with 2 different chargers. My "small" battery goes to 42.2V.

When my bigger (newer) battery shuts off all groups are consistent, but at 3.6V. Almost to the 3rd digit after the coma.

And I was running the butteries (so far separately) - so 2p vs 4p. with a 25% range improvement and GOOD improvement on acceleration and climbing.

At this point I am waiting for a 10s4p battery replacement. So I will have the third battery (same 'crappy' as the second bigger one).

I can't change what i deal with (other that trowing it away). I can check if the groups are OK, and the internal resistance of the groups, and the whole batteries, but other than that I am stuck.

As I said: so far I was using each battery alone, and switching (I gave up the electric switch - just plug-unplug - I change the ports for convenient ones.

IS THERE ANY REASON TO DO THEM IN PARALEL to increase the range or it won't matter.

Open for any suggestion.

I understand, that I didn't buy the most efficient scooter, and my replacement battery is a 'cheap' substitute. But the contraptions is not expensive, and it runs. I am trying to 'beat the odds' a little to the limits of what I can and can't. I appreciate the advice.
_______________

With the 10s4p battery I had a problem to start with - it came broken. The last 4 battery group tests 0.0V. I disassembled it and found 1 battery physically damaged. I replaced the whole group with the batteries I had and then charged the group to the consistent voltage before connecting. I checked the internal resistance - it matched. It doesn't heat up. it works, but I do not expect miracles.

I will get a new replacement some time (#6 weeks) all from China.

But it all boils to the question - is it working and can I push it. this is the whole point of inquiry. I am pretty satisfied (provided what I had in my hands) with the result - but running it in parallel - would it extend the range, or just use the batteries more safely? Sorry for such a trivializing question - but this is what I actually want to know.

I won't be offended if you tell me to go away because I wanted something which is impossible. But let me know. Thanks.

(I am a professional photographer - I changed, modified, improved probably all of my equipment. But since I am not an expert in many things [Except photography] - I ask questions and heed the advices)

 

[JMK1000]

One more thing:

When I use the these two packs of batteries in parallel - I assume, that I should disconnect them for charging, right?
And, I assume, I shouldn't keep them connected when not in use.
Am I thinking correctly?

Thanks again for your help.

 

[JMK1000]

HI, I just want to clarify:
You wrote:
Since you are getting the same range even though you now theoretically have about three times the amount of capacity ("6p" vs 2p, even if 4p and 2p are not used at the same time), the new pack must only last you a very very short time to not add any range to the system with the old pack. That won't change if it's paralleled, until you fix whatever is wrong with the pack that causes such an extremely low capacity.
_______

About the range - when using the packs separately - say I have about 6.5 miles range from 10s2p, and when I switch to the 10s4p about 8miles with much better acceleration and climbing power.

So, 2 batteries - range 2+ times better.
If I switch to parallel packs, can I keep the same?

 

[amberwolf]

Ah, the way you had posted the previous information made it sound like the packs were possibly already paralleled, which then implied that the new pack was really horrible.

As previously noted:

basically since the current draw is divided between the packs when paralleled, the load on each one is less, so the packs are not pushed as hard, and they get both a longer lifespan, and at least a small amount more of usable capacity than if they were used separately. (it might be such a little amount it's irrelevant to your needs, but it might be enough to give you noticeably more range than you had with each one independently, used one after the other).

So while you would have to test the actual results, in principle you should see better performance with them paralled, than with either individually.


And yes, I would disconnect the outputs from each other when charging, though it should be safe to parallel the inputs during charging (and disconnect when not charging).


As to whether you can "push it", I have no way of knowing. That depends on the quality of the packs, what they are designed and actually built to do, vs what you intend to demand of them. The farther you go past design intent and actual parts capability, the more likely something will age faster than desired or actually fail.

 

[JMK1000]

Thank you Amberwolf!

I will do the testing today or tomorrow. The principles of connecting and using both batteries in parallel I understand. But, taking under consideration that both batteries charge to a bit different voltage( .5V difference) and shut off at different voltage, I have to make sure that it works in practice.
I am waiting now for the replacement of the 10s4p from China. I fixed the first battery (as I wrote one group was completely damaged, and replaced by me - individual groups perform almost identically after the fix). Hopefully the new battery will come un-damaged, and I will be able to test it against the one I fixed.

I am not expecting miracles. This is only 250W motor with max output around 500W - the controller limits the current to 12A. So, I am not going to put more money in it. I will run it until I get something more advanced, newer, better.

Thanks again. I will post the results of the tests soon.