Quote:
Originally Posted by Love To Travel 2
Jim,
I am guessing that you would normally connect the meter on the house battery, not on the coach/engine battery. Would it be prudent to get two meters and hook one to each system? Also in layman's terms, can you explain the purpose of the shunt that has to be installed? Does it come with the meter or is it something extra that you purchased? And did you wire yours before the main coach shut-off switch? Thank you!
Ed
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I love these kinds of questions because it reactivates the electronic technician brain cells that aren't being used much during retirement.
These meters should be wired directly to the house battery because that is what you need to monitor and it is best to monitor at the source. Measuring downstream will give different results. When wired to the battery you will end up running 3 wires from the battery area to the meter's location: +12 volts, ground, and the current measurement wire.
When current flows though any wire some of the voltage will be dissipated across the wire due to the resistance in the wire. The more resistance in the wire, the more voltage will be dropped across it. This is a fact and the reason you need heavier gauge wires when pulling more current so the voltage drop across the wire is minimal. This voltage drop can be measured and is what is happening when a shunt is used.
A shunt is nothing more than a chunk of metal with a known resistance. When inserted inline with a battery feed, the shunt will drop a very small voltage across it. I haven't measured this actual voltage drop but assume that it is in microvolts or milivolts since the shunt is a good chunk of metal. If you were to hook up a meter across the the shunt your meter would be able to measure the very small voltage that would be there. That is what the meter is doing in these displays. It is actually measuring microvolts (or maybe milivolts) and not current. They design these things so that their voltage measurements equate to the amount of current being drawn. Hope this makes sense.
As far as putting one on the coach battery, that would be a waste. You don't need to monitor a constant draw from that battery because you have no control over it. Besides, when you engage the starter, MAJOR current is drawn and your meter may not be able to handle it. Instead, just plug a voltage monitor into the cigarette lighter (old term, now called a power outlet) and just look at it now and then.
When I camp I use the coach battery to recharge electronic devices (phones, pads, my drone, etc) through a multi-tap usb charger. Doing this causes the battery to slowly lose power. When I see it get down to about 12.3 or 12.4 I will charge it back up. Being an electronic geek I naturally came up with an easy way to recharge the coach battery rather than having to start the engine.
I purchased an RF relay that I connected to the rig's relay that connects the coach battery and house battery together when the engine is running. I can trigger the rig's relay by pushing a button on a little keychain. Then my house converter can charge all batteries at once. I also have solar which will recharge everything. When I engage (like captain Picard would say) my remote relay I can see the voltage reading go way up on my display that is plugged into the front power outlet. I let it run for a few hours which is enough to bring the coach battery back up to a good level. I then shut off my relay and wait days until the voltage drops again to a level where I want to recharge.
All of my mods (maybe I should say toys) have worked perfectly for years. I love gadgets (wife just loves this quirk about me, maybe not). Computers, electronics, and whatever. Love it all. Oops, I am getting off topic because I got a little too excited.
Anyway, please feel free about asking me any electronic questions. Before I retired I was in tech service where I helped other technicians troubleshoot electronic things. I miss it more than I want to admit. These days I only get asked by my wife why certain things don't work like they should. Like "why didn't the remote change the tv channel to what I had selected". You get my drift.
, I will take that. Geek is good.
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