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I'm upgrading the battery on my electric boat. Currently I have a 72v 100ah LifePO4 battery. I have a solenoid between the controller and the battery. That solenoid is attached to the ignition key.
I just bought 2 more batteries and I intend to put them in parallel. I'm going to install a solenoid on each one, and then join them on a bus bar, which will then go to the main line to the main solenoid, which goes to the controller.

72v solenoid

Solenoid

The goal will be to have a switch on the dashboard for each battery. I want to put an indicator light next to each switch to show the contactor is closed and power is flowing from one side of the solenoid to the other.

I understand there is a way to add a diode on each the positive and negative and then connect an LED's positive in the middle, like this:

Diode Assembly

solenoid assemply

  • Is this even how this works?
  • what kind of diode should I use for a 72v system?
  • Is there a better way?

Thanks for your help.

Pᴀᴜʟsᴛᴇʀ2
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Daniel Morris
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1 Answers1

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If you have an LED for each solenoid you don't need diodes as shown- that would be to have an LED illuminated if either of two voltages was present.

Rather you can just put an LED with an appropriate series resistor across each solenoid coil, with a diode such as 1N4004 in inverse parallel.

For example, if you want ~7mA through the LED you could use a 10kΩ 1W resistor.

schematic

You may also need fusing to protect the wiring depending on how exactly it is built. That's outside the scope of this answer, but you certainly don't want the possibility of 72V at enormous current appearing across a thin wire under any possible fault condition.

Also note that this does not show "that the contactor is closed", rather it shows that there is voltage across the coil. If the contactor has failed the LED will still illuminate.

If you want to show what is going on in terms of current flow, I would suggest considering using bipolar DC Hall sensors on each battery lead which can show charging and discharging to each individual battery, virtually without losses.

Spehro 'speff' Pefhany
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