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48v isolation switches stopping 58v pylontech batteries?

Fraser

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Mar 25, 2021
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Hi everyone. I bought pylontech batteries and along side them I wanted to be able to isolate them. (Extra safety) because they can be turned off. They say you have to isolate the negative and positive. Now is that because 48v isolation switch isn’t enough on a 58v battery and it somehow works if you put one on negative as well?
Greatly appreciative of any knowledge on that.
Thanks Fraser
 
there could be additional parasitic current pathways thru communications cables or something else where just disconnecting the positive is not entirely disconnecting the battery, maybe...
that said... I would never put an isolation switch into a system that is rated to handle LESS than the voltage of the device; nope, not a good idea.
That has "marketing team found a way to save money on production" written all over it.
 
there could be additional parasitic current pathways thru communications cables or something else where just disconnecting the positive is not entirely disconnecting the battery, maybe...
that said... I would never put an isolation switch into a system that is rated to handle LESS than the voltage of the device; nope, not a good idea.
That has "marketing team found a way to save money on production" written all over it.
there could be additional parasitic current pathways thru communications cables or something else where just disconnecting the positive is not entirely disconnecting the battery, maybe...
that said... I would never put an isolation switch into a system that is rated to handle LESS than the voltage of the device; nope, not a good idea.
That has "marketing team found a way to save money on production" written all over it.
Thanks for the reply.
I will have to ask the company that sells this stuff why they sell these isolation switches along side these batteries and why isolate both positive and negative.
your strong reply suggests it is just as well you can switch the batteries off.
I feel in a better position to ask the question to them now.
Thanks again.


 
I have a similar issue. I have a 16 cell "48V" LiFePO4 battery (not pylontech) that is fully charged at just under 58V. I've been looking for a suitable battery disconnect switch. My max load is 75A and I have 100A fuses and 200A wiring.

I only isolate the positive on disconnect. I don't plan to disconnect the negative. I also don't have fuses on the negative. This means that my negative ground is always connected and I don't have any uncertainty of where ground is. That said, I do have a fast acting fuse and mushroom style emergency disconnect switch in the middle of the pack which would split the 48V pack into two 24V packs reducing the highest voltage present if required. This fuse is capable of interrupting thousands of amps safely in the case of a battery short, and the mushroom style emergency connect switch is capable of interrupting the full 100A DC. I don't plan on using this switch except in an emergency.

I don't see why a switch on the positive and another on the negative would increase the switch rating if below the voltage of the battery. Disconnecting DC under load can cause arcing, which could cause a fire if the switch isn't rated for that voltage and the arcing persists. I don't think switching two switches at once would do much to reduce the arcing because I doubt the two switches could be operated perfectly simultaneously and therefore the first is subject to interrupting the full load, if it arcs, then the second will get a high load and may arc also.

Looking high end, BlueSea (and others) have a max of 48V:

I don't know if that means they can be used on a 48V nominal system with voltages up to 58V or the 48V is absolute max since most boats that these BlueSea switches go into run either 12 or 24V systems. 48V is still not commonplace yet! Anyone have any experience to offer?

I have found these 60V 100A (300A max) switches all over eBay and AliExpress, there are many stores that supply what appears to be the same thing:

I bought one and pulled it apart (see photos attached) and it looks quite well built inside with a 1.5x10mm copper bar with 10mm square pads so I calculate it will handle 100A quite well, I just don't know about the gap when switched off that a spark would have to jump is sufficient for 60V DC. Can I trust their rating of 60V and is it too close to my max battery voltage of 58V anyway? I've only been able to test it with 54V 25A so far, but there is no noticeable heating of the switch over a long period with that load. I haven't switched it under load as I don't want to do anything to my charger. I'm not sure what the circular groves on the pads are for, perhaps for arc extinguishing? At this price I can't expect any fancy arc suppression stuff and there aren't any magnets that could do that.

I also have a 4 cell "12V" LiFePO4 battery and I'm confident using these switches for that, just unsure about 58V.

At the moment I am thinking of using the 60V switches with my 48V battery pack, but I won't switch them under load, I'll ensure the 48V motor is off before switching them since I can use the mushroom emergency disconnect switch if required to interrupt a load and the 48V motor also has its own contactor capable of stopping it under load. I'll also monitor the switches for heat. These switches are very compact which is very helpful as I don't have much space. Any thoughts or recommendations?
 

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I don't know if that means they can be used on a 48V nominal system with voltages up to 58V or the 48V is absolute max since most boats that these BlueSea switches go into run either 12 or 24V systems. 48V is still not commonplace yet! Anyone have any experience to offer?
I have found these 60V 100A (300A max) switches all over eBay and AliExpress, there are many stores that supply what appears to be the same thing:
We've been running a 48v solar system for about 18 months. I used the cheap Harbor Freight battery disconnect switches on the solar input and the battery, and they work fine. Fusing the battery was not difficult as I used a giant ANL type 100A fuse. The odd problem was in fusing or protecting the panel input to the charge controller--it can be up to 100v unloaded and about 70-80v at 25-28 amps in full sunlight. I put in a commonplace AGU type 40 amp fuse in a cheap holder intended for automotive stereo applications--the fuse worked fine for more than a year, until it popped on a very hot sunny day. I never saw more than 30 amps in that circuit, but the fuse holder got very hot, melting some of the plastic. So the voltage and power going thru that circuit (it never saw more than 1900 watts max) is a little too much for some "automotive" type hardware. But the Harbor Freight disconnect switches have given no problems.
 
I use double pole DC circuit breakers, appropriately sized, as shutoffs when needed.

Always use the spec sheet for switches and fuses. Nominal does not apply.

Fuses, breakers and switchgear is NOT the place to save money.
 
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