Ezrider_028
10 mW
Can I connect a 7v battery in series with a 48v lithium battery ? These both having the same cell types 3.7v and 2.6ah ? Both battery packs have 20ah.
Batteries in series question.
- Thread starter Ezrider_028
- Start date
docw009
1 MW
You can connect a 7V battery to a 48V battery and have a nominal 55V, Peak voltage when both are full charged is 63V,
The problem is you will probably blow up the transistors on the battery management system (BMS) on the 7V battery. The BMS is what prevents you from overcharging the battery or running it too low, Its transistors are likely only rated for 36V and you have the above 63V, so there's a real chance they can be damaged.. Then you'll have a fire risk.
You can look up the part numbers on the MOSFET transistors on the 7V BMS and find out their voltage rating, This is a 12V BMS, and it uses 5030L's. They are 30V transistors. Would probably blow up at 48V. I was using a 12V battery and a 36V battery to get 48V, but only for a short time. I was lucky this BMS didn't blow up.
If you're not using a BMS on that 7V battery, well you should, Is it 2x7?
The problem is you will probably blow up the transistors on the battery management system (BMS) on the 7V battery. The BMS is what prevents you from overcharging the battery or running it too low, Its transistors are likely only rated for 36V and you have the above 63V, so there's a real chance they can be damaged.. Then you'll have a fire risk.
You can look up the part numbers on the MOSFET transistors on the 7V BMS and find out their voltage rating, This is a 12V BMS, and it uses 5030L's. They are 30V transistors. Would probably blow up at 48V. I was using a 12V battery and a 36V battery to get 48V, but only for a short time. I was lucky this BMS didn't blow up.
If you're not using a BMS on that 7V battery, well you should, Is it 2x7?
Chalo
100 TW
I don't see how a 2S BMS would have any way to find a voltage potential over 8.4V, since it's not connected electrically to the other end of the companion pack.
docw009
1 MW
Nothing will happen when the load is running. The 7V BMS is on, and you have minimal voltage across the transistors. Run the 7V pack down to 6V and it will shut off. The transistors go open circuit, and see the full potential of both packs across the BMS. Yes, the current path also goes to the original load. but you don't need much current to pop a transistor.
I ran the above board on a 12V battery with a 36V pack a few times to get 48V. No problems because it never shut off, so it never saw the high voltage. I also never knew about the issue til it was covered here in this forum.
After that guy with two 48V packs in series posted here about one catching on fire while riding, I started to belive the theory could actually happen.
I ran the above board on a 12V battery with a 36V pack a few times to get 48V. No problems because it never shut off, so it never saw the high voltage. I also never knew about the issue til it was covered here in this forum.
After that guy with two 48V packs in series posted here about one catching on fire while riding, I started to belive the theory could actually happen.
Ezrider_028
10 mW
Thanks all, on the 7v side I have a total of 8 cells (3.7v 2.6ah ) and the configuration will have 2 series 4 pairs totaling 7.4v 20ah along with a 2s 20ah BMS. On the other battery pack I bought a 48v 20ah battery from CAO MM, so I wanted to experiment connecting them in series. Both packs have separate BMSs.
This experiment was after my friend loaned me his 52v 30ah battery and I really enjoyed the speed bump on my 48v 15000w motor.
My controller capacitors have a 63v limit so i think im ok by no pushing full throttle on a full charge, and I also vetted the Mosfets.
This experiment was after my friend loaned me his 52v 30ah battery and I really enjoyed the speed bump on my 48v 15000w motor.
My controller capacitors have a 63v limit so i think im ok by no pushing full throttle on a full charge, and I also vetted the Mosfets.
DaLanMan
10 kW
Ok, now that ya'all have come to the same conclusion I had.. ::grins:: I feel rather validatred.
If this would cause a fire, it would also cause a fire whenever you put *ANY* group into series.
I have a set of 12 12v battery packs all with their own management in each unit, some of them went out in parallel pairs to be battery boxes. A few have a new home on my bench, they are the sacrificial few, the proud, the batteries that are going to one day have a glorious event where they let out the MAGIC SMOKE!! pffft POOT
Sorry, was running away with meself. I wanted those batteries because it occurred to me. I don't have to wait til I am done building a battery pack, run a group of those up in whatever config needed and you end up with a perfect lil test bed, they are well insulated well armoured. It is kind of the perfect solution.
I have even put them in series with the battery *in* a bike (ok, it sounds brave, I already ordered a replacement bit of kit so I can get hte battery pack out, it is kinda wedged because some idiot ::looks around with shifty eyes:: tried to shove wires past it...
In any case, worked like a champ, managed to test a 24v system at 48v, turns out everyone was happy, no fires no booms.. Total disappointment.
I imagine I probably read that somewhere, I doubt I am honestly bright enough to have thought that far ahead, and if I did.. my fellow rangers will be very disapoint.
If this would cause a fire, it would also cause a fire whenever you put *ANY* group into series.
I have a set of 12 12v battery packs all with their own management in each unit, some of them went out in parallel pairs to be battery boxes. A few have a new home on my bench, they are the sacrificial few, the proud, the batteries that are going to one day have a glorious event where they let out the MAGIC SMOKE!! pffft POOT
Sorry, was running away with meself. I wanted those batteries because it occurred to me. I don't have to wait til I am done building a battery pack, run a group of those up in whatever config needed and you end up with a perfect lil test bed, they are well insulated well armoured. It is kind of the perfect solution.
I have even put them in series with the battery *in* a bike (ok, it sounds brave, I already ordered a replacement bit of kit so I can get hte battery pack out, it is kinda wedged because some idiot ::looks around with shifty eyes:: tried to shove wires past it...
In any case, worked like a champ, managed to test a 24v system at 48v, turns out everyone was happy, no fires no booms.. Total disappointment.
I imagine I probably read that somewhere, I doubt I am honestly bright enough to have thought that far ahead, and if I did.. my fellow rangers will be very disapoint.
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