Connecting 2 x 48V 15Ah kettle battery packs in parallel
- Thread starter swen
- Start date
dogman dan
1 PW
Others may disagree, but I'd just connect them up. Put two plugs for input on your controller wire.
Series is what gets tricky for the bms. Parallel should be ok.
Series is what gets tricky for the bms. Parallel should be ok.
Drunkskunk
100 GW
Pro- you have twice the range.
con- Ummmm... its heavier?
Pro- The load will be shared between both packs, causing less voltage sag and contributing to longer life of both batteries.
con- well... You won't be able to justify buying a new battery in a few years when a better battery is invented and available, because your old battery is still working fine?
con- Ummmm... its heavier?
Pro- The load will be shared between both packs, causing less voltage sag and contributing to longer life of both batteries.
con- well... You won't be able to justify buying a new battery in a few years when a better battery is invented and available, because your old battery is still working fine?
gwhy!1
100 kW
just make sure that both batterys voltages are within a volt each other before you join them up.. you dont want to connect a flat battery in P with a fully charged battery that would not be a good idea 
Drunkskunk
100 GW
If there is a difference in voltage, the battery with the higher voltage will dump it's extra voltage into the other battery, limited only by their internal resistance. At .01 ohms each, a 2 volt difference would cause the higher voltage battery to be dumping power into the other battery at 100 amps. That could melt your cabling and connectors, cause damage to the cells, and possibly start a fire.
Just keep them paralleled all the time, and there isn't any reason why they should have different voltages.
Just keep them paralleled all the time, and there isn't any reason why they should have different voltages.
999zip999
100 TW
The details what about some. One new one old ? What cells ? Where they come from ?
dogman dan
1 PW
Sorry I didn't understand which details you needed.
Voltage must be equal. Charge fully then connect. "48v" can be 13 cell that charges to 54v or 14 cell that charges to 58v. So make sure the packs are really compatible with each other. Not one lifepo4 and the other limn. They need to be more similar, and preferably nearly identical.
However, they don't have to be the same capacity. You can hook a 10 ah up to a 20ah. As they discharge, the 20 ah will drop voltage slower, and the result will be more electrons flow from it. Even if no flow from the 20 ah to the 10 ah is possible, it will more or less balance out and both will reach empty close to the same time. Most bms today will allow some flow from one pack to the other, so in that case, they will stay the same voltage the entire ride, with a small flow from big pack keeping the small one the same voltage. No harm done, which is why I said go ahead and parallel. It won't wreck your bms.
They don't have to be the same quality either. As long as they are the same chemistry type and cell count, you can run a high quality expensive pack in parallel with a cheapo pack.
Charge separately, unless you have rewired the two to run on one batteries bms. I was not assuming you wanted to get that into it. Just plug in two batteries, run them together. The unplug them from each other to charge. Faster to run two chargers anyway when it's time to fill up.
Very nice to have two batteries. Carry one when only one is needed. Carry two when you have a long ride in mind. Supplement range of one expensive pack with a large cheapo pack is what I do.
Voltage must be equal. Charge fully then connect. "48v" can be 13 cell that charges to 54v or 14 cell that charges to 58v. So make sure the packs are really compatible with each other. Not one lifepo4 and the other limn. They need to be more similar, and preferably nearly identical.
However, they don't have to be the same capacity. You can hook a 10 ah up to a 20ah. As they discharge, the 20 ah will drop voltage slower, and the result will be more electrons flow from it. Even if no flow from the 20 ah to the 10 ah is possible, it will more or less balance out and both will reach empty close to the same time. Most bms today will allow some flow from one pack to the other, so in that case, they will stay the same voltage the entire ride, with a small flow from big pack keeping the small one the same voltage. No harm done, which is why I said go ahead and parallel. It won't wreck your bms.
They don't have to be the same quality either. As long as they are the same chemistry type and cell count, you can run a high quality expensive pack in parallel with a cheapo pack.
Charge separately, unless you have rewired the two to run on one batteries bms. I was not assuming you wanted to get that into it. Just plug in two batteries, run them together. The unplug them from each other to charge. Faster to run two chargers anyway when it's time to fill up.
Very nice to have two batteries. Carry one when only one is needed. Carry two when you have a long ride in mind. Supplement range of one expensive pack with a large cheapo pack is what I do.
Leebolectric
1 kW
Great tips, taking them in.
So, on this topic, my questions are...
1- Suppose I have two 52v12.5ah triangles...both new and ready to use.
As they wear...and eventually loose some capacity...what if one is able to charge to 58.5v and the other only charges to 57v at "100%"?
Would the voltage difference make them go BOOM when connected parallel? ....do they need to be exact?
2-I think you are saying the parallel connector should be removed from the batteries leads BEFORE charging.
Would they balance to each other better if connected? ...or am I just electrically stupid? :lol:
Two chargers, operating at the same time, one for each battery, then once unconnected from charger, add the parallel adaptor?
3-anything I should watch out for?
I use all xt90s connectors for battery connections...and xt60 for charging.
Should I take everything outside when doing the parallel connection?
What would be the ACTUAL reaction be if this was done wrong? what kind of Boom? fire? smoke? spark?
(just in case something bad happens, i wanna know what's happening so i can respond fastest.)
Probably use this guy...
So, on this topic, my questions are...
1- Suppose I have two 52v12.5ah triangles...both new and ready to use.
As they wear...and eventually loose some capacity...what if one is able to charge to 58.5v and the other only charges to 57v at "100%"?
Would the voltage difference make them go BOOM when connected parallel? ....do they need to be exact?
2-I think you are saying the parallel connector should be removed from the batteries leads BEFORE charging.
Would they balance to each other better if connected? ...or am I just electrically stupid? :lol:
Two chargers, operating at the same time, one for each battery, then once unconnected from charger, add the parallel adaptor?
3-anything I should watch out for?
I use all xt90s connectors for battery connections...and xt60 for charging.
Should I take everything outside when doing the parallel connection?
What would be the ACTUAL reaction be if this was done wrong? what kind of Boom? fire? smoke? spark?
(just in case something bad happens, i wanna know what's happening so i can respond fastest.)
Probably use this guy...
Drunkskunk
100 GW
swen said:
That would be best, yes. It's not critical, as long as you insure they both reach the same charged voltage. It might be easier to balance your pack with them separate, and if it is, do it that way.
Your battery is actually a collection of cells wired together in parallel. wiring in another pack in parallel is the same as adding more cells to the first pack. Effectively, you just have one large battery while they are wired together.
Leebolectric said:
Assuming they are lithium batteries from the same charger, if you have voltages that are that far out after a charge, take them carefully out of the house and place them on a fireproof surface away from any standing structures until you can determine what the fault is. You may be about to have a fire.
The 57V pack may have a dead cell. That could cause the other cells to be overcharged if you used a bulk charger or a BMS that couldn't shut down the charger for a failed cell. Assuming NMC lithium, those could explode at voltages over 4.3 volts. a dead cell and a charge of 57 volts means you would have 4.4 volts on each cell.
Leebolectric
1 kW
all hypothetical, just questions to understand better, thanks.
don't these 18650 cells loose charge capacity over time?
Like after 300 cycles...and run heavily...do they ALWAYS reach full "100%" charge?
at that kind of wear...not a bad cell...don't they get lower top end or something?
I'm wondering, if when I use one for short rides...will it wear out faster than the other one that only goes on long rides paralleled?
I probably should alternate them for the short rides to wear them equally?
don't these 18650 cells loose charge capacity over time?
Like after 300 cycles...and run heavily...do they ALWAYS reach full "100%" charge?
at that kind of wear...not a bad cell...don't they get lower top end or something?
I'm wondering, if when I use one for short rides...will it wear out faster than the other one that only goes on long rides paralleled?
I probably should alternate them for the short rides to wear them equally?
Drunkskunk
100 GW
Cool. Cells keep the same charge and discharge voltages, they just lose capacity in between.
Leebolectric
1 kW
so, you're saying, they will always read the same voltage numbers when full and empty...no matter how old...
...it will just burn those amp hours faster for fewer overall miles once it wears?
Sorry for dumb questions...but it's making better sense with each one
...it will just burn those amp hours faster for fewer overall miles once it wears?
Sorry for dumb questions...but it's making better sense with each one
Drunkskunk
100 GW
No worries. You pretty much have it. except you don't burn amp hours faster. You just lose the use of some of those amp hours.
A cell that starts with 10 amp hours capacity loses a little bit each time it's used. after 300 cycles, it might lose 20%, so it now works like an 8 amp hour cell. That lost 2 amps is made up of small parts of the inside of the cell that have gone bad and aren't usable anymore.
A cell that starts with 10 amp hours capacity loses a little bit each time it's used. after 300 cycles, it might lose 20%, so it now works like an 8 amp hour cell. That lost 2 amps is made up of small parts of the inside of the cell that have gone bad and aren't usable anymore.
Leebolectric
1 kW
Excellent, I get it.
so...on the opposite theme...series connection....
Assuming the same two batteries, 25r 18650 triangles with 52v12.5ah each...
Can I connect the two and get a 104v12.5ah battery? (so I could run a different higher voltage system)
Will the BMSs and everything accept this configuration? would it confuse the controller?
What would that wiring diagram look like compared to the "parallel" connector?
I have one parallel connector, prebuilt...but I don't know what is going on INSIDE it exactly.
(sorry for hijacking your thread Swen)
so...on the opposite theme...series connection....
Assuming the same two batteries, 25r 18650 triangles with 52v12.5ah each...
Can I connect the two and get a 104v12.5ah battery? (so I could run a different higher voltage system)
Will the BMSs and everything accept this configuration? would it confuse the controller?
What would that wiring diagram look like compared to the "parallel" connector?
I have one parallel connector, prebuilt...but I don't know what is going on INSIDE it exactly.
(sorry for hijacking your thread Swen)
nutnspecial
10 MW
Yes. . . wow, 104 is alot.
Yes, it would confuse the controller poor thing would go braindead lol. You'd need a controller rated for that voltage. Another consideration is the motor would have 2x the topspeed.
Volts for motor speed, amps for motor power. Watts is overall measurement.
Also, bms's would conflict I think, but I don't know much on them.
Instead of ++ -- going to the controller, it would be + (+-) - for series.
Absolutely right on the idea that cell voltages remain the same, with just less capacity inbetween overtime. A pack unable to charge completely would either be charger, bms, a cell, or a bad bms or cell connection in the pack.
If one pack has an issue it'd be better to get resolved. I think connecting 2 packs 4v off will throw sparks, trip bms's, and maybe melt connectors. Not sure, little exp with bms's and the problem isn't clear. Results depend on the initial problem.
Yes, wear is dictated by cycle life. The pack getting more use will drop capacity quicker, but it doesn't hurt to parallel different capacity packs (like even 10 + 20ah). Voltage needs to match for parallel so they don't try to equalize voltage hurting the smaller set of cells with overcharge, and AH should match for series so the cells on each side reach bottom of charge at the same time. If AH in parallel is unmatched, lower capacity side will bottom out their voltages first. That will kill cells not bms'd, but w/bms it would prob just shut that low pack down.
Yes, it would confuse the controller
poor thing would go braindead lol. You'd need a controller rated for that voltage. Another consideration is the motor would have 2x the topspeed. Volts for motor speed, amps for motor power. Watts is overall measurement.
Also, bms's would conflict I think, but I don't know much on them.
Instead of ++ -- going to the controller, it would be + (+-) - for series.
Absolutely right on the idea that cell voltages remain the same, with just less capacity inbetween overtime. A pack unable to charge completely would either be charger, bms, a cell, or a bad bms or cell connection in the pack.
If one pack has an issue it'd be better to get resolved. I think connecting 2 packs 4v off will throw sparks, trip bms's, and maybe melt connectors. Not sure, little exp with bms's and the problem isn't clear. Results depend on the initial problem.
Yes, wear is dictated by cycle life. The pack getting more use will drop capacity quicker, but it doesn't hurt to parallel different capacity packs (like even 10 + 20ah). Voltage needs to match for parallel so they don't try to equalize voltage hurting the smaller set of cells with overcharge, and AH should match for series so the cells on each side reach bottom of charge at the same time. If AH in parallel is unmatched, lower capacity side will bottom out their voltages first. That will kill cells not bms'd, but w/bms it would prob just shut that low pack down.
don't forget that if the 2 batterys have slightly different internal reistance then one will act like a load to the other, its one of the main reason you have dual battery kits in cars (and the fact you don't want a fridge to drain all juice and not be able to start the car)
Actully hooking up a dumb solenoid would be a great idea, eg batterys are in 2 separate banks enless key is on (or switch) then the 2 packs are in parrell, these are made to handle big loads (eg winching a 4x4)
they could then be charged separately or together
Actully hooking up a dumb solenoid would be a great idea, eg batterys are in 2 separate banks enless key is on (or switch) then the 2 packs are in parrell, these are made to handle big loads (eg winching a 4x4)
they could then be charged separately or together
nutnspecial
10 MW
I think that works better on lead acid with far less voltage range (sub 1v). Doing that between a partial and full charge liion would not be great without pita safeguards to level the packs slowly?
Leebolectric
1 kW
Is this diagram correct? (those are supposed to be TrianglePacks^)
Yes, 104v was hypothetical and crazy...I guess two 36v batteries could give me 72v which is more common.
paracidium
1 mW
104v isn't crazy, I've just made that voltage setup using a Lyen 12 fet 4115 84-132v controller. I have enough spare lipo to to run at even higher voltage (150v being the absolute limit for the fets). I just had to include a pre charge resistor in my circuit for connecting the packs because it makes quite a spark if you don't . Only other thing I made sure of was that all my connections were well terminated and as waterproof as possible (don't fancy getting a shock from 130vdc in the rain whilst connecting!)
. Only other thing I made sure of was that all my connections were well terminated and as waterproof as possible (don't fancy getting a shock from 130vdc in the rain whilst connecting!)
Drunkskunk
100 GW
Perfect diagram. No harm going with 104 volts, as long as the controller and motor can take it.
The party starts at 100.
The party starts at 100.
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