Batteries in parallel

Eastwood

100 kW
Joined
Jan 13, 2021
Messages
1,437
So I’m considering getting another identical battery 72v 20ah and connecting parallel to have 40 amp hours. Also would have double the amp output :mrgreen:

So my current battery has a discharge port and a charging port. I use regen through the discharge port although there’s no BMS protection from the regen or ebrake but I have the voltage cutoff set in the controller.

So my main question is with charging in parallel. Do I just charge through one battery because they’re connected on the discharge? Seems like the second battery would get charged through the discharge port if stayed connected. Obviously there will be no BMS protection through the discharge port, same as my regen.

Or do you connect the charger ports in parallel?

I really don’t want to disconnect and reconnect the batteries every time I need to charge. Would be much more convenient if I can charge through one port. What’s the best way about doing this?

As stated above I’ll be using regenerative braking.


I found some helpful info on this thread.
https://endless-sphere.com/forums/viewtopic.php?t=93304
 
Its good to have the same amount of resistance going to each battery when charging. So if you had a parallel wiring connector it wouldnt make much sense for one pack to have a 2 foot lead and the other a 4 inch lead.

You could daisy chain them like you suggested, but the second pack would have slightly more resistance and would lag behind in state of charge and voltage. Yes they would quickly equalize after a charge since they are hooked up in parallel.
 
Bulk charging to 90% through the discharge port for regular charging, and fully charging the packs separately through their charge ports to balance the packs occasionally is the way I would go.
 
E-HP said:
Bulk charging to 90% through the discharge port for regular charging, and fully charging the packs separately through their charge ports to balance the packs occasionally is the way I would go.

Ok that makes sense, thanks! :thumb:

Do you see any issues with using regen in parallel? I would think the amps would go back into each battery at the same rate?
 
Also if both batteries have 80 amp BMS limits, then I should have no issue running 160amps from the battery(s) right?

I’ve considered a new battery with a higher output of around 200amps but my current battery is not that old, fairly new. So I figured it would make more sense just to get an identical battery and run them in parallel, just hoping I don’t have issues with running 160 A from the battery
 
Eastwood said:
Do you see any issues with using regen in parallel? I would think the amps would go back into each battery at the same rate?

Nope, can't assume that. Internal resistance of the cells increase with use, so even if both packs use the same cells, your existing pack will already differ from spec/new. One pack make accept more of the regen energy than the other, but my guess is probably not enough to be an issue.
 
Regen will be fine, the battery with the lowest voltage and resistance will accept more, but it should be similar enough to not be an issue. Same happens with discharge btw, the strong pack taking the load more than the weak. Volts and resistance changes as the packs discharge, so at some point they equal out, and each pack should reach the end at the same time, unless one pack is damaged, like a dead cell in there somewhere. If you connect a shit battery to a good one, when the damaged packs bms cuts it off, the other pack will be going, "thank god you took that extra drain off me".

But with the bms involved, best bet to separate the packs and charge each one on its own charger. Connect only when both are full as they can get, to run parallel discharge.

Its not an issue to run 80 amps from each battery, unless you don't want to beat both batteries into dogshit, in one season. Seriously, you parallel them to make them last, unless its a racing bike. No battery likes running at its max spec. But you like it while it lasts. :twisted:
 
dogman dan said:
Its not an issue to run 80 amps from each battery, unless you don't want to beat both batteries into dogshit, in one season. Seriously, you parallel them to make them last, unless its a racing bike. No battery likes running at its max spec. But you like it while it lasts. :twisted:

Yeah I’ve been contemplating just building a new battery with a higher discharge rating.
Don’t have a spot welder and I’ve never built a battery before though.

It would be cheaper for me to just buy another 20 amp hour but then I’m stuck with slightly less performance then I’m seeking. Plus like you mentioned pushing the battery's to the max is not good for longevity.

I’ve been looking at these cells. Thinking maybe 23s 16p would give me 320amp discharge. Probably would go with a 300 amp bms
Epoch 25P 18650 2500mAh 20A $2.99
 
ZeroEm said:
You're not going to be happy with 23s, to much voltage. 22s not full charged is better. Maybe you have a 150v controller ready to go.

Yeah actually after more measuring the 23S would be too hard to fit with the larger amp hour. Probably will stick with just 20s :|
Controller, Svmc72200 unlocked :thumb:

Well when considering the 23S I was looking at the svmc96120 unlocked but the battery is just too long for my frame. So either I’ll build 72v40+amp hour or just buy another 72 V 20 amp hour like I have now run them in parallel. The problem is I buy another battery I would have less amps to play with but it’s a lot cheaper.
 
Have a 24ah on my trike and another 24ah that I wanted to mount during the build but never have. I get tired of sitting before the battery is discharged. Two I could ride fast and far.
 
ZeroEm said:
Have a 24ah on my trike and another 24ah that I wanted to mount during the build but never have. I get tired of sitting before the battery is discharged. Two I could ride fast and far.

What’s your peak wattage?

My battery power peaks at 6.7kw And my 20ah battery will drain fast. Sometimes I lower the amps to get better range but it’s just not as fun :mrgreen:
I can kill the battery down to 20% pretty quick when at full power and off road.

On road is a different story I can get much better efficiency. Maybe around 30 miles if the amps are turned down. If the controller is turned up maybe less than 20 miles lol
 
New the battery was 1.8kw, 36a continuous, 60a BMS. My controller is a 40a. Have had the amps turn up to 40a (3200w+) to play. Have it set at 35a at the moment. I don't off road, ride greenways 15mph and out on the Hwy's ride faster and can go about 80mi. If I keep between 15-20 mph should get between 100-150mi on a charge. Depends on wind and what roads. With both I can go farther. :shock:

by Eastwood » Sep 30 2021 7:07pm

ZeroEm wrote: ↑Sep 30 2021 5:50pm
Have a 24ah on my trike and another 24ah that I wanted to mount during the build but never have. I get tired of sitting before the battery is discharged. Two I could ride fast and far.
What’s your peak wattage?

My battery power peaks at 6.7kw And my 20ah battery will drain fast. Sometimes I lower the amps to get better range but it’s just not as fun :mrgreen:
I can kill the battery down to 20% pretty quick when at full power and off road.

On road is a different story I can get much better efficiency. Maybe around 30 miles if the amps are turned down. If the controller is turned up maybe less than 20 miles lol
 
Well just purchased another 72v 20 amp hour battery. Considered hard building a new battery but this route was much cheaper, Plus my other battery is less than one year old. So will have 40 amp hours now and can safely discharge 160A :thumb:
The batteries are identical, same cells and same BMS

Thanks for the input everyone!
 
Where did you buy the new battery from?
I need additional 1.5-2kwh maybe even 3kwh, thinking ev batteries myself.

Eastwood said:
Well just purchased another 72v 20 amp hour battery. Considered hard building a new battery but this route was much cheaper, Plus my other battery is less than one year old. So will have 40 amp hours now and can safely discharge 160A :thumb:
The batteries are identical, same cells and same BMS

Thanks for the input everyone!
 
markz said:
Where did you buy the new battery from?
I need additional 1.5-2kwh maybe even 3kwh, thinking ev batteries myself.

Got the battery from UPP, my 3rd battery from them. The other purchases I got off Amazon but this time I bought it directly from UPP because I needed a different BMS which will now ship from China. They had this battery in US stock two day shipping but different BMS.
Paid $580, :mrgreen: Way cheaper than building the massive battery I had planned :lol:
2500mAh Chinese cells :pancake:
 
ZeroEm said:
$580 for 72v 20ah is dirt cheap. Grin has a 24ah for $1,200. I paid $900 for 24ah 3yrs ago. Hope it lasts.

Yeah for sure dirt cheap :mrgreen:
My current UPP battery I have pushed hard and it still performs well. I’ve had this battery for about 10 months and I would say it has around 100 charge cycles. Have the controller set to 80 A rated and peak with no heat issues. Also have charged this battery at 8amps :? with no issues, but I don’t do that often it’s just when I’m charging on the go. So yeah I’ve pushed this battery really hard so gives me hope that I should get at least 2 to 3 years based on the performance I’m still getting at 10 months. Now that I’ll have a second battery I can stop beating this pack into the dirt lol

When the time comes and this battery starts to die off I can just replace the one. From my understanding eventually they will both level off while in parallel as the new battery will provide more current in the beginning.
 
Yeah, just wait for sales.
I got a deal on the Satiator charger when I bought the 52V 14.5Ah 40A battery on sale from them.
Much better then making a battery yourself. You'll end up like our friend es: LateCurtis with piles and piles of batteries and never using them.

I wish I lived close by Grintechs warehouse so I could swing by and look at their bargain bin. Maybe grab a Phaserunner or something else cool with cosmetic damage. See beauty is on the inside.

ZeroEm said:
$580 for 72v 20ah is dirt cheap. Grin has a 24ah for $1,200. I paid $900 for 24ah 3yrs ago. Hope it lasts.
 
Best battery deals I’ve found at batteryhookup.com
Best battery I found was lying in the junkyard for pennies on the dolla covered in mud and abused and neglected. Lol.

Nicce old thread resurrection tho. Lol.
 
The best deal I found was that one guy from Sausalito that was willing to rewind a Savox motor for my still not finished Ebike project. If I ever ask for another motor rewind I'm going to pay him more money, he's far too humble, lol.

Btw that LRK winding is suuuper smooth. You just cant find that kind of voodoo with an off the shelf motor. :mrgreen:
 
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