DIY Digital Dual Battery Volt Metre

[nj swb]

You could simply use an spdt relay (NO NC relay) as pictured below.

Just wire as follows:

85 - Power from momentary switch
86 - Earth
87a - Power from main battery (or accessories)
87 - Power from auxillary battery
30 - Power out to voltmeter

I did something like that in Shorty:

Well, after a little too much mucking around, the front now looks like this:



And the back looks like this:



Essentially, it switches the factory voltmeter between the starting battery and the auxiliary battery.

I could've used a simple double throw switch, but that would be too simple. That, and I couldn't find one that I liked. So I have a push button (with blue LED) and a latching relay circuit. On start-up, the voltmeter will show the starting battery voltage. Push the button, and it displays the auxiliary battery voltage, and the blue LED is on to remind me.

I couldn't find a suitable switch to revert to the start battery, so I have to turn the ignition off to reset. But, with my system, if the aux battery is charging then the starting battery will be too, so I don't think it will be a significant nuisance. And it's all been done without cutting a factory wire, although I did drill / cut a few holes.

Now I just need to go away to test it.

I made it a little more complicated than necessary, because I wanted a discrete switch, and was more interested in auxiliary voltage than main - with Shorty's system, if the auxiliary was charging then the main would be too.

I was happy with it.

Edit: on my phone, the photos were fine. On my computer, they were blurred & watermarked. They're now hosted on this forum.