Jonasan-san
10 mW
I'm looking for a way to hook 4 separate batteries together with a blender and can only find blenders that allow for 2 batteries so I'm wondering if I can use 3 blenders to hook them all together?
Can I daisy chain battery blenders?
- Thread starter Jonasan-san
- Start date
You should ask the manufacturer/vendor.
Chalo
100 TW
Are you using batteries of different voltages? Because if they're all the same nominal voltage, you'd be much better off skipping the gimmicky power-wasting nonsense and just connecting all the batteries in parallel after charging them fully.
If they are packs of different voltages, then it would probably be better to use them sequentially rather than in parallel (if the individual packs are sufficiently powerful enough to run the bike by themselves).
If they are packs of different voltages, then it would probably be better to use them sequentially rather than in parallel (if the individual packs are sufficiently powerful enough to run the bike by themselves).
Jonasan-san
10 mW
I've had a chat with Justin and he told me there's a small chance outside of user error to start a fire because of a dead cell when connecting batteries in parallel so I'm really not interested in doing that. I'm set on the blender.
Chalo
100 TW
Using that gadget won't eliminate the chance of fire due to a faulty cell in your pack. So don't incorrectly think you're avoiding that risk if you have janky packs.
Jonasan-san
10 mW
Justin specifically said using the blender avoids that risk. I'll believe him.
Chalo
100 TW
It offers some protection in limited conditions, mostly related to a strong pack backfeeding a failing pack. It does not prevent a faulty pack from catching fire, at all. Don't be fooled about that.
Jonasan-san
10 mW
I doubt anything would. I would never buy a pack from Ali Express, Amazon etc. Only reputable dealers.
abagofcells
1 mW
I don't see any reason why it wouldn't work, but each battery blender looses a bit of energy through resistance in a MOSFET or voltage drop over a diode, depending on internal construction. I also don't think it will be necessary to use three of them, just two, connecting each battery, and the outputs from the two blenders should be fine to connect together.
Did you have to spend much money on these "blender" things?
JackFlorey
100 kW
Most "blenders" are just diodes or active diodes. So you can connect two of them to the same battery. No reason to put them in series.
JackFlorey
100 kW
They're around $150 a piece.
Wow! I was guessing maybe $15. They must be laughing all the way to the bank. Caveat emptor!
Some of them claim to have programmable microcontrollers in them to actively manage the battery connections, using FETs to switch connections on and off, etc. (but the parts to do this probably still don't cost more than a few dollars)
lnanek
1 kW
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- Sep 26, 2022
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- 450
$26 one I use works fine:
You do need a motor with a clutch and controller that can disable regen, though.
You do need a motor with a clutch and controller that can disable regen, though.
JackFlorey
100 kW
What losses are you seeing during operation?
lnanek
1 kW
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Haven't noticed any. There's plenty of FETs and shunts in the BMS and controller, what's one more pair.
Biggest issue I run into is my weakest battery can only handle 20A before the BMS shuts down and forces me to turn the battery off and on again to use it. My other battery can handle 30A. I can't set the max battery amps on my controller to 30A, though, because sometimes the blender will choose to discharge only the weaker battery, and then pop, on the next hill that uses max juice, shutdown. Have to turn that battery off and back on again to get it contributing. With only one battery I can't go full throttle the 20 miles to work the whole way, so it's pretty noticeable. Without the weaker battery contributing, bike rides a mile or two short.
So biggest limitation in my book is that you have to set your controller's max battery amps to cater to your weakest battery. If I did one of the other hacks floating around, like plugging the weak battery into the charging port of the stronger battery, probably wouldn't have that issue.
Biggest issue I run into is my weakest battery can only handle 20A before the BMS shuts down and forces me to turn the battery off and on again to use it. My other battery can handle 30A. I can't set the max battery amps on my controller to 30A, though, because sometimes the blender will choose to discharge only the weaker battery, and then pop, on the next hill that uses max juice, shutdown. Have to turn that battery off and back on again to get it contributing. With only one battery I can't go full throttle the 20 miles to work the whole way, so it's pretty noticeable. Without the weaker battery contributing, bike rides a mile or two short.
So biggest limitation in my book is that you have to set your controller's max battery amps to cater to your weakest battery. If I did one of the other hacks floating around, like plugging the weak battery into the charging port of the stronger battery, probably wouldn't have that issue.
Sounds like a terrible design for the blender. If it were a good design it would leave all batteries connected all the time so they would discharge together. Then the only time the individual battery properties would come into play is when one of them exceeds an internal limit and shuts down, which would take longer and be predictable as to when it would happen (as it would always happen under the same conditions and timing, given the same battery state of charge, ride conditions, etc).
lnanek
1 kW
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- Sep 26, 2022
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- 450
Yeah, ideally, if one of my 48V batteries was 46V and the other battery 45V and I'm drawing enough power via the controller that effectively it would pull them both below that via voltage sag, I don't think they would be charging each other in that situation anyway.
So ideally there would be no battery blocked at that point. Unfortunately, at least for the simple minded one I have, it's always just highest voltage battery is on and other is off, apparently. I have heard people do crazy things and connect, say a 52V battery and a 48V battery to these things. So I suppose they just want to be extra safe... or extra cheap. Connecting a fully charged 52V and fully charged 48V battery without anything between would be a very sudden and large amount of current from one to the other after all, perhaps faster than any sense circuit. I have noticed my weaker battery has lower internal resistance as well, though. So it is a weird situation where it tends to drain preferentially even at the same voltage despite being less Ah.
Common port BMS do famously measure current and even if they want to disable discharge, if the the charging current is ~1.5A or so, they enable the discharge FET anyway to avoid the voltage drop of going through the internal body diode for no reason when the current shows it is charging and not discharging anyway. So theoretically this sort of current sensing optimization logic is possible.
So ideally there would be no battery blocked at that point. Unfortunately, at least for the simple minded one I have, it's always just highest voltage battery is on and other is off, apparently. I have heard people do crazy things and connect, say a 52V battery and a 48V battery to these things. So I suppose they just want to be extra safe... or extra cheap. Connecting a fully charged 52V and fully charged 48V battery without anything between would be a very sudden and large amount of current from one to the other after all, perhaps faster than any sense circuit. I have noticed my weaker battery has lower internal resistance as well, though. So it is a weird situation where it tends to drain preferentially even at the same voltage despite being less Ah.
Common port BMS do famously measure current and even if they want to disable discharge, if the the charging current is ~1.5A or so, they enable the discharge FET anyway to avoid the voltage drop of going through the internal body diode for no reason when the current shows it is charging and not discharging anyway. So theoretically this sort of current sensing optimization logic is possible.
If you have to connect different voltage batteries, it would be a lot better to just use a pair of schotkey diodes, one on the + output of each battery as a Y cable. Then whichever is the higher voltage would contribute until it was equal to the other (like during voltage sag), and then simple resistances would take over for how much current each contributes at any instant.
Ideal diodes (FETs turned on) would be even better, less voltage drop, but would need extra circuitry to determine which pack is higher voltage and turn the other pack's FET off until they are equal. It's not too complex to do, and doesn't require MCUs or anything, but it's still extra stuff that unsimplifies the behavior.
Ideal diodes (FETs turned on) would be even better, less voltage drop, but would need extra circuitry to determine which pack is higher voltage and turn the other pack's FET off until they are equal. It's not too complex to do, and doesn't require MCUs or anything, but it's still extra stuff that unsimplifies the behavior.
lnanek
1 kW
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Yeah, some of the descriptions for the FET based ones claim they can dual discharge when voltage is equal:
Never seen it from mine, though. Top review seems to say the same:
Perhaps the super expensive DateX ones do a better job of it.
Never seen it from mine, though. Top review seems to say the same:
Perhaps the super expensive DateX ones do a better job of it.
Chalo
100 TW
What I interpret is that they might become only slightly inferior to paralleled batteries when the voltage is equal. Whee.
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