Maybe a dumb question but...

[Daffyh]

Does running 2 batteries in parallel increase current output?
eg. 2 batteries with 20 aH CDR doubles current to 40aH?

Cant get a straight answer from Google some say yes others say no.

Controller is a 17/30 aH peak.
Bafang 1000W rear hub.

 

[Daffyh]

Cheers i think Ohms law helps as well. I have sort of answered my own question from seat of the pants results and I'm sure the nay sayers about running 2 in parallel will appear shortly.

 

[fooferdoggie]

Does running 2 batteries in parallel increase current output?
eg. 2 batteries with 20 aH CDR doubles current to 40aH?

Cant get a straight answer from Google some say yes others say no.

Controller is a 17/30 aH peak.
Bafang 1000W rear hub.

well you cant safely run two batteries at the same time they don't discharge at the same rate and they are not synced together. But if you want to burn your bike up it will work for that. there are things that can regular the voltage between two batteries I have heard. but most bikes with two batteries dont use them both at the same time.

 

[Gionnirocket]

Yes, current in parallel is accumulative.
But for the reasons Mr. Foofer gives, I wouldn't attempt it especially when implementing cheap hardware that states it can do so.

Best to run one battery and then the other.

 

[Chargeride]

well lithium bike batteries are a load of cells in parallel to give a higher amperage, but they are all linked by a battery management system
.
I guess you could wire both batteries to one BMS, but that's just not practical unless they are identical and its all permanently attached in a bomber style ebike custom frame.
I do see two batteries simply doubled up in those bikes, but you take your chances, and you are the BMS.

 

[teskow]

Most diesel pickups run two lead acid batteries parallel. I believe they only have one voltage regulator. The batteries are identical and expect they must be to work correctly.

 

[harryS]

The controller asks for a specific current. If the battery can provide it, that's what you get, If not, you get only what the battery can do.

Putting two batteries in parallel allows you to draw a total current equal to the sum of their rated numbers. It won't happen unless the controller calls for it,

Not going to discuss the risks/hazards of batteries in parallel. There are ways you can go wrong so be careful. Read up on it and make your own choices.

 

[Daffyh]

I've read a lot i use the 'dangerous' connector box.
Of course its risky life is a calculated risk.
I have really shitty disabilities that limit everything i do if it blows up so be it.

 

[Chargeride]

Most diesel pickups run two lead acid batteries parallel. I believe they only have one voltage regulator. The batteries are identical and expect they must be to work correctly.

Lead acid can withstand massive charge currents without bursting into flames

 

[PCeBiker]

Lead acid can withstand massive charge currents without bursting into flames

My 48V 25Ah battery has a 30 amp BMS but can only charge at 4 amps.
Why is that?
I know it has something to do with the internal resistance of the battery that creates heat, but wouldn't that internal resistance be the same whether the battery is charging or discharging?

 

[Chargeride]

You can have high rate lithium, lipos etc
The battery in a hybrid car is very high discharge/charge, makes them very expensive for their ah rating.

Some hybrids only have a 1kwh battery, it just charges and discharges at 100s of amps.

If you want to research why li ion is slow, you will be sent down a rabbit hole of ions and carbon and car parking analogies.

 

[Slaphappygamer]

My 48V 25Ah battery has a 30 amp BMS but can only charge at 4 amps.
Why is that?
I know it has something to do with the internal resistance of the battery that creates heat, but wouldn't that internal resistance be the same whether the battery is charging or discharging?

The way I understand it, the BMS regulates the charging current, as well as the discharge current (30amps). What cells do you have?

 

[PCeBiker]

If you want to research why li ion is slow, you will be sent down a rabbit hole of ions and carbon and car parking analogies.

I've fallen down enough rabbit holes with my e-bike already. I don't want trip into another one.
I've got three batteries now and I'll just use them how I'm supposed to.
I don't want to know about better batteries, cause then I'll want one.

It just seems weird that my BMS can safely discharge my battery at up to 30 amps continuous, but when you put the charge back in, you can't go past 4 amps. 0.2C or less is the recommended charge rate.

 

[PCeBiker]

The way I understand it, the BMS regulates the charging current,

I don't think that's right?
At least with my BMS's.
I've got a 2, 3, and 4 amp charger and my bench power supply will put out 5 amps.
I can charge all my batteries with all my chargers and my power supply.

The batteries will take as much current as you give them, and the BMS doesn't restrict the current until the maximum voltage is met.

as well as the discharge current (30amps). What cells do you have?

My 19ah and 21ah batteries are 18650 cells, and I believe they are both Samsung cells.

My 25ah battery uses Samsung 50E 21700 cells

 

[PCeBiker]

I use my bench power supply to charge my batteries.
I only charge to ~50 volts at 2 amps, charging indoors with me watching the charging as it happens.
It's essentially a manually operated Grin satiator, but I get to see the voltage and current in real time.

The power supply is right under my TV and I can keep an eye on it as the charging happens.

It's quite exciting watching it switch from constant current to constant voltage.
Way funner than watching the red light turn to green on a regular charger.

Then, after the current drops to zero, I shut it off and top it up to 54.6 before my next ride.

I just started charging to 51.6 volts so it doesn't take as long to top it off before my ride.
That's ~80% charge, so not too bad to let it sit at that for a few days until my next ride.

 

[Gionnirocket]

I don't think that's right?
At least with my BMS's.
I've got a 2, 3, and 4 amp charger and my bench power supply will put out 5 amps.
I can charge all my batteries with all my chargers and my power supply.

The batteries will take as much current as you give them, and the BMS doesn't restrict the current until the maximum voltage is met.



My 19ah and 21ah batteries are 18650 cells, and I believe they are both Samsung cells.

My 25ah battery uses Samsung 50E 21700 cells

Charge is limited by the capability/quality of the BMS circuitry. It would need to be beef'd up and more expensive to facilitate a faster charge.
Then you'd need to deal with the heat generated.
Since fast charging isn't considered necessary and potentially decreases safety... It's just not implemented.

 

[Tom@WashDC]

if it blows up so be it.

If it does "blow up" please post pictures, or, have your next of kin post pictures on your behalf.

 

[PCeBiker]

The way I understand it, the BMS regulates the charging current, as well as the discharge current (30amps). What cells do you have?

I just checked my 25 Ah battery and it says 5 amp charge,..

But there's a 10 amp fuse on the charge port inside the battery,..

So it looks like I could charge at up to 10 amps.
I would NEVER Do that BTW.
I charge at 2 amps, because it's better for the battery (less heat) and I've got the time.

I don't want to pull 5 amps out of my power supply either. It should last longer if I don't max it out.

The most I've turned it up to is 3.5 amps to top up to 54.6V quicker before a ride.

@m@Robertson has 3 identical Wanptek power supplies and 2 of them have crapped out on him already.
He does like to turn things up to Maximum though.

I make sure the automatic fan in the power supply isn't running constantly.
Heat is bad for the charger too.

 

[PCeBiker]

Then you'd need to deal with the heat generated.

Do the lithium cells or the BMS generate more heat while charging as compared to discharging?

Is that why my battery can discharge at 30 amps, but can only charge at 5 amps? (Or 10 amps if I use the fuse. )

 

[Gionnirocket]

I'd guess equally if properly configured.
But do you ever pull 30a. continuously? If you did, you'd probably have one warm pack that wouldn't last very long.
Ability to high discharge is needed for the intended use.. Charging is not and would have added negative affect.
Most power tools have fast charging because it's deemed necessary. They're quite warm out of the charger.