48v and 52v parallel, what’s the voltage?

Bobby

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Hello,
If I connect a 48v 13ah to a 52v 13ah battery in parallel I should get 13+13= 26 amp hours, but what would the voltage be? Would the voltage be 52v or 48?
Thanks.
 

Bobby

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The 52v would charge the 48v until they were equal somewhere in between 48 and 52v.
Do you think it’s ok to connect this two batteries? My controller is rated at 48v, but I’m mostly concerned about damaging my battery. I didn’t think the potential difference was that much, but after doing some research it seems like the potential difference between the two batteries could damage them.
 

midnightventure

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I personally would not do it. Nothing would happen right away but I don't think it do either battery good. It would probably harm the higher voltage battery faster since it would be getting pulled down all the time. I'm sure about my first answer but don't really have for sure knowledge about this one. And the lower voltage one would be operating like it was on a charger when it didn't need to be on a charger.
 

Nelson37

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STUPID, DANGEROUS IDEA!!!

Do NOT do this.

OR, if you do, please inform us where we can get in on a pool for your fire and life insurance.

If you want the electrical info, lets see, the two batteries will equalize at an in-between voltage, dependent on cell capacities, in an exceptionally short period of time, wires may melt, lower voltage battery will likely blow the BMS, but may overcharge cells, they may explode or catch on fire, starting a thermal runaway where adjacent cells overheat and catch on fire, etc.

This could result in cells from the higher voltage battery being dangerously Undercharged, with similar results to above. less likely, but still possible. blowing the second BMS also a possibility.

The least damaging result would be one blown BMS.

As for most damaging, there are dead people who have tried this. Houses burned down. Livestock slaughtered.

OK, not that last one.
 

Nelson37

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Holy crap. First, simple Y cables will do the same job.

Second - No mention whatsoever of the requirement that both batteries being paralleled be at same voltage. NOTE-** This is with batteries with the same DESIGNED voltage, that they be charged to near-identical voltages, generally recommended to be no more than a tenth of a volt or two off.

AGAIN - parallel two batteries, the voltage difference is equalized EXTREMELY RAPIDLY, with whatever volts and amps is required moving over the connecting cable in less than 2-3 seconds. Have seen pictures of copper cables explosively vaporized and molten copper landing on exposed hands, fingers, faces, etc.

Please note we have not even gotten into actually USING the two batteries, charging, BMS issues, etc., look into balancing and consider two different BMS units, cells with different capacities and output rates, BMS with different limits and schemes, it is a nightmare which absolutely no one who has a clue what they are doing would recommend.

I make a point of finding such people and listening to them. Dude who made that video is NOT repeat NOT one of them.
 

solliex

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I run a 20 amp and a 15amp 52 volt system on my Juiced Scorpion X. I never would connect both at the same time!! I have a switch on both batteries, and just turn one on at a time. Works great, and I can do it while still riding. It also makes it easy to keep both batteries from reaching below 20% (46 volts for me) extending the batteries life. Yes two batteries are great for battery health, as well as fixing anyone’s ”range anxiety”……

 

Capt Kirk

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Hello and as someone who has worked with lithium batteries for 15+ years and yes we have been using these batteries in R/C planes for a while. When it comes to running parallel lithium cells, you want the SAME Voltage, same amperage and same battery chemistry. Any attempt at this will only prove to be an expensive and possibly the end of anything attached to the batteries, bike frame motor,etc. This may work kinda but I advise getting 2 identical batteries from the same manufacturer with matching voltage and ampacity. When charging lithium batteries only charge 1 pack at a time, and try not to rush the process. Lithium is not like Nicads or or lead acid and an incorrect charging sequence will definately get a response from the local Fire dept. IMO, hub drives are great for level commuter riding, mid drives give you the gear advantage. Proper gear selection before you need it reduces the wear and tear on your chain and cassette, shift before the hill, not while you are climbing it. I have converted a 26" MotoBecane Fantom Pro using the BBSHD, and have 300+ miles, the cassette and chain are still shifting smoothly, and this is only used for Flow trail riding but climbs anything I point it at. Good luck be safe, and keep a bucket of sand near your charging station
 

BretCahill

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I have an old 36v BMZ that was once rated at 11 amp hrs but is more like 4 amp hrs now.

The circuit board of the BMZ has 4 large wires, a black and red going to the Rosenberger connector and a black and red going to the cell stack.

So I wired a 36v 20 amp hr battery in parallel directly to the cell pack of the old battery.

Both batteries are now charged and discharged through the old electronics. This setup shouldn't have any significant effect on the BMS of either battery, charging or riding.

I put a 15 amp fuse between batteries as the 500 watt motor never draws more than 18 amps according to the GO Swiss Drive monitor.

If the larger battery is 1 volt higher than the smaller when connected the current is only 1/4th an amp -- small compared to the charging currents and smaller still compared to riding.

Just make sure the rated voltages are the same.

The BMS of the old battery is now logging 6X more charge than previously and will be confused as to why the voltage is so high when the amp meter indicates it should be almost dead.

As before the bike will run all the way down to 32 v at which time it shuts down. In the meantime anything related to charge on the monitor will be disabled.

It may recalibrate for the additional charge when it gets down to 32v and shuts down. GSD doesn't output volts so until then I don't ride far from the charger w/o a volt meter.

Depending on the charge I can do 8 - 15 km/volt in the highest assist.

I should have bought a 10 amp hr battery. I look at that big battery with dread. Take all week to recalibrate the monitor. Never buy a battery with more range than you can pedal.
 
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