Use Blue Sea 7700 to connect batteries-Opinion

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jerothle asked Jul 8, '23

Use Blue Sea 7700 to connect batteries-Opinion

Hello, I would like your opinion... I have several large capacity lithium batteries and have the Blue Sea 7700 remote battery switch attached to each. I want the 7700 to connect or disconnect each individual battery. There is a remote switch that can be attached to the 7700 allowing it to be switched on or off from a remote location. I thought it would be good to have the yellow lever on top of the 7700 accessible by hand for maintenance, checking the batteries individually or even in an emergency (to disconnect the batteries quickly).

With the remote switch wired to the 7700, physical access to the yellow lever might not be necessary?

I look forward to any input/opinion on this.

Thank you, Jeff

battery switch safety control

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Answer 1 · 2023-07-08T06:17:01Z

hjohnson answered · Jul 08, 2023 at 06:17 AM

The complication with the 7700 is that it's bi-stable, so you basically need to pulse one wire to turn it on, and pulse a different one to turn it off, but most controls are built for a single wire (ie voltage high = relay on, voltage low = relay off). There are circuits to do this, but it's a bit beyond the scope fo this forum. I actually use a 7713, which emulates a normal contactor, for my main disconnect, and I picked it for precisely the same reason as you; I can lock it off if need be and/or manually turn it on if i want to.

However I would urge you to reconsider this plan in its entirety. You really do not want to normally be connecting/disconnecting your large lithium batteries, especially if they wind up at significantly different states of charge. You will cause extreme currents to flow as the batteries try to balance with each other. You are much better off leaving them connected together, and only breaking the parallel chain if you absolutely have to.

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