Parallel Battery packs

Hi all,

I have two battery packs. 13s6p and 13s4p
Both with BMS

I have tried it and it works fine.
My intention is to make the battery have less discharging load and so less voltage sag during peak and longer battery life
PS: i need different packs since i don't have space in the bike to put it together as 13s10p pack

I know that whenever two batteries connected together in parallel, the higher voltage will 'charge' the other one.
My question are:
1. My BMS have different input and output socket. So this means that whenever the packs have different voltage. The 'charge' will coming from output port. Is it ok?
Anyone knows what will happen if you charge a battery from the output pins/port?
2. How big the 'charging' current going to be? Lets say the difference around 1v (54v vs 53v). Is the bigger volt gap the bigger ampere going to be or is it going to be the same charging current whatever the voltage gap is?

Thanks

1. It is my understanding that this can be done, but there is no overcharge protection from the BMS.

2. It is my understanding that the current involved is at whatever level is necessary to equalize the voltage in a fraction of a second. A full volt is way too high. Somewhere between one tenth and one hundredth of a volt seems to be where the desired value sits. There does seem to be some variance of opinion on this.

If the wires melt, it was too high.

If you want to equalize two packs that are at slightly different voltages (SOC) you can hook them together with a resistor to limit the equalization current. For example, if there is only 1 Volt difference, a 1 ohm resistor would limit the current to 1 amp. Once the voltages are nearly equal, you can remove the resistor and hook the packs directly in parallel.

From my notes, HA02 is the way to go

ZHC battery equalizer balancer
Shenzhen Huaxiao Technology Co., Ltd

passive energy transfer method, any SoC, high rate

HA01 HA02 HA03

detects mV level difference between two batteries
20mV (10mV?) level triggers shunt current from higher voltage battery
to the lower voltage one,

HA series can be used to equalize lead acid battery (VRLA), Lithium Iron Phosphate Batteries ( LFP), Nickel Cadmium Secondary Batteries (Ni/CD), and Nickelmetal Hydride Secondary Batteries (Ni/MH) lithium ion. 

HA02 4x batteries or fewer, any chemistry, starts at 2.4V so possibly while in use
in series or in parallel
or presumably also if otherwise isolated

not necessarily just 4Sx12V=48V, multiple units can be connected for more blocks

**10A** balance current!

https://zhcsolar.com/product/ha02-battery-equalizer

HA03 for 8 units, $300!
no, just use 2xHA02, half the price

I have 2 each, 51.2V nominal, 12 Amp Hour LiFeP04 packs I run parallel but are separated by a key switch on each. I use .2 to .3 Volts as my maximum differential to connect the packs together. One day I'll measure the equalization current but the wires are very difficult to get to. If they are further apart, I'll just ride a very short distance to bring the high pack down.

AngryBob said:

If the wires melt, it was too high.

Click to expand...

Thanks Bob

Volt_Ampere said:

For example, if there is only 1 Volt difference, a 1 ohm resistor would limit the current to 1 amp. Once the voltages are nearly equal, you can remove the resistor and hook the packs directly in parallel.

Click to expand...

Where do i need to put the resistor? do you have the scheme?

john61ct said:

From my notes, HA02 is the way to go

Click to expand...

Nice info!
But this only 12v so how to stack it?
I see on the google that one of the 12v battery need to connect to both HA02, means if i have total of 12v x 8 i need at least 3 x HA02?

If i connect it to the 12v section in the battery pack (3sXp?) Will it affecting the BMS connection?

BVH said:

I have 2 each, 51.2V nominal, 12 Amp Hour LiFeP04 packs I run parallel but are separated by a key switch on each. I use .2 to .3 Volts as my maximum differential to connect the packs together. One day I'll measure the equalization current but the wires are very difficult to get to. If they are further apart, I'll just ride a very short distance to bring the high pack down.

Click to expand...

If you got a chance, please also monitor the current after both are connected to parallel when in idle. I wonder even after they equalize, are they will still charging each other periodically (sudden changes in the internal volt inside the battery)

Thanks all

Hot what's hot if it to hot to hold. Yes use your hand as a temp sensor but easy you don't have to grab it and get within half an inch of it and you know if it's hot or not

kuririkura said:

Nice info!
But this only 12v

Click to expand...

Nope, I don't think that's even true for the HA01 though that's how it's marketed and must be over 10.5V.

But the 4-port HA02 can do anything over 2.4V.

I think 2 units will cover 8 strings, afaict it doesn't care whether serial or parallel or combos.

I would parallel / bypass the BMS but really, best to get guidance from them or a good reseller, there are plenty.

Or start a new thread on 3-4 different forums with

ZHC HA02 parallel balancing gadget wiring

in the title

kuririkura said:

please also monitor the current after both are connected to parallel when in idle. I wonder even after they equalize, are they will still charging each other periodically (sudden changes in the internal volt inside the battery)

Click to expand...

Only if things go wrong, sort of thing you'd use a fuse for protection.

Too many parallel strings can bring unbalanced issues, but once connected OK they're not safety issues, just reduced capacity and longevity impact.

Which I believe the HA02 is the magic bullet for, likely others that do the same, I think maybe these https://www.electriccarpartscompany.com/BALANCERS-EQUALIZERS

not recommending that seller BTW.

kuririkura said:

My question are:
1. My BMS have different input and output socket. So this means that whenever the packs have different voltage. The 'charge' will coming from output port. Is it ok?
Anyone knows what will happen if you charge a battery from the output pins/port?
2. How big the 'charging' current going to be? Lets say the difference around 1v (54v vs 53v). Is the bigger volt gap the bigger ampere going to be or is it going to be the same charging current whatever the voltage gap is?

Click to expand...

When you charge a battery thru its output port, the overvoltage protection circuits may be bypassed, if they're only on the discharge side. The compromises battery safety if your charger happens to fail and put outtoo much voltage.

In your case, you would have battery A charging battery B so there won't be an overvoltage case, but you could exceed the charge currents for the internal cells, depending on how careless you were when connecting them in parallel. If the differential is small, the current will be minor, but if you put pack A at 54 volts on pack B at 40 volts, there's nothing limiting the current on pack A.

I have some small 10S2P packs that I run in parallel. Here are some numbers taken with my RC wattmeter when they are paired.
1) .20 volt difference, 42.0 to 41.8 volts. .25A flows as the lower battery is almost full.
2) 1.2 volt difference. 41.8 to 40.6 vols. 2.0A flows until the packs equalize..

To answer your second question, a battery naturally takes less current near full charge. If I did the 1.2 volt difference at 60% charge instead of 95% charge, I am sure the currents would be way higher. They will also be higher with larger packs. Mine are only 2P, so 6P and 8P would take at least 3X and 4X more current than what I posted.

So keep them as close as you can in voltage when you connect them. Break them apart for charging. You can probably trust they are equal when they come off the charger. I do with mine, but if I'm unsure, I just measure them.

docw009 said:

I have some small 10S2P packs that I run in parallel. Here are some numbers taken with my RC wattmeter when they are paired.
1) .20 volt difference, 42.0 to 41.8 volts. .25A flows as the lower battery is almost full.
2) 1.2 volt difference. 41.8 to 40.6 vols. 2.0A flows until the packs equalize..

Click to expand...

Thanks! Really nice to know some real world number.

My personal opinion the number of parallelism wont really affect the amps (only maximum)
Since the charging power (joule/watt) is related to (VxV)/R but also not sure how to get the 'R' value on this case.

Looking at your meter result seem difference up to 1v will still be safe, even if the more parallel battery involve might trigger greater amp, at the end it will be also splited to the same parallel number
Lets say 3x your number (6A) of charging divided by 6p still just around 1A per cell, still below the 1C of typical maximum cell charging

A month late to the party in this group but was wondering if in the case of having two parallel batteries discharging at say 8 amps each to give a total of 16A, if it would be sensible to place an ammeter at the output of each battery. Placing a display for each ammeter on the handlebars.

Couple of scenarios where I thought that might be useful:

1. If one batt is shut off by the bms, and the other batt ends up taking all the 16A load, user can see that only one batt is draining hence making it difficult to reconnect the batteries until each are fully recharged/discharged.

2. If internal resistance in one batt increases/decreasea (unsure how this would happen), and the ratio of current output from each battery is 10A to 6A, user can see the difference I'm currents and stop riding to prevent different rates of discharge.

Alternatives could be adding a 15A fuse on each battery, but that does not solve issue number 2.
Could then add a Cycle Analyst or Batt-man wattmeter alongside the 2 panel mounted ammeters to monitor Wh/Ah, voltage etc.

This is what I plan to do with my design. Any thoughts?

Thanks.

N.

I have (2) same 48v 10A Li-ion battery pack with built in BMS with 2 same charger as well. If i decide to connect them in parallel after charging them to their max voltage or the same identical voltage with the 2 chargers separately and each time i decide to charge them i separate them and repeat the process of charging them to an identical voltage reading before reconnecting them would i have any issues when using them in the parallel mode?

Also the max drain for each pack is 20A so when they are connected in parallel would the max drain increase to 40A or close to that?

Or suppose i am pulling 30ah constant would this mean i am pulling an estimate of 15ah from each pack once the packs are at the same or close to the same voltage?

It would be very rare for the draw to be equal even though voltage/SoC goes down together,

but that is a symptom of issues not a cause, in the end as long as they're both healthy, they end up getting to empty.

More gadgetry in the discharge path adds risk of failure and some resistance / voltage drop.

Discharge amps will increase, only if the previous pack was a bottleneck.