Hi, I'd like to add a voltmeter to the dash on my motorhome. It's on a Ford E-450 chassis. I'd like the voltmeter to come on with the key (accessory power), and I'd also like to install a pushbutton switch on the dash I can use to see the voltage without the key. I probably should have bought a 3 wire one, but I like the size & style I picked out and it happens to be a two wire one.
I can see two fairly straightforward options. I'm looking for feedback on them or other ideas.
The first one is to use a relay. I would need to use diodes so I don't backfeed power into the accessory circuit. This option would also draw more current from the battery due to the relay. Which isn't an issue when the vehicle is running and honestly probably isn't really an issue when it's not running either. I would use switch when, for example, I want to check the voltage to see if the 5W solar charger is keeping the battery charged. Or if the battery was discharged and I'm charging it from the motorhome electrical system and want to keep an eye on it.
One downside to this idea is if you toggle the switch while driving, the voltage reading may change (due to where it's being sampled from). Which is fine, just kind of weird.
The 2nd idea is to use a normally open / normally closed switch to toggle where the voltage is read from. In "normal" mode the voltmeter is connected to accessory power, so it just comes on with the key. But if I toggle the switch it samples from the battery or some other always-hot source in the fuse panel. This kind of switch is a little harder to find, most of the simple round push button switches on ebay only have two contacts.
Thoughts? Thanks.
I can see two fairly straightforward options. I'm looking for feedback on them or other ideas.
The first one is to use a relay. I would need to use diodes so I don't backfeed power into the accessory circuit. This option would also draw more current from the battery due to the relay. Which isn't an issue when the vehicle is running and honestly probably isn't really an issue when it's not running either. I would use switch when, for example, I want to check the voltage to see if the 5W solar charger is keeping the battery charged. Or if the battery was discharged and I'm charging it from the motorhome electrical system and want to keep an eye on it.
One downside to this idea is if you toggle the switch while driving, the voltage reading may change (due to where it's being sampled from). Which is fine, just kind of weird.
The 2nd idea is to use a normally open / normally closed switch to toggle where the voltage is read from. In "normal" mode the voltmeter is connected to accessory power, so it just comes on with the key. But if I toggle the switch it samples from the battery or some other always-hot source in the fuse panel. This kind of switch is a little harder to find, most of the simple round push button switches on ebay only have two contacts.
Thoughts? Thanks.
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