Adding a Digital Volt Meter to show battery state of charge

[NetBoy]

Hi, I decided to add a digital volt meter to my motorhome to show the state of charge of the batteries - it will be handy when dry camping.

Here is a table from the web site "The 12 Volt Side of Life" that shows voltage vs state of charge (a great web site to learn about living on 12 volts):


I ordered a digital volt meter from eBay for $5 including shipping:



I mounted the meter, and a momentary contact switch, in a piece of plastic from an old car litter basket:




I will mount the meter in some convenient location in the motorhome tomorrow. And I'll include a printout of the above voltage chart.

Pretty cool for five bucks!

Note that battery voltage should be read when the batteries are at "rest" -- that is, wait a half hour after any big discharge (for example, such as running a microwave on an inverter).

[NetBoy]

1rosario wrote:
What local store might have a digital meter?
We're leaving Sunday, too soon to order off eBay.

Camping world carries a little digital volt meter that plugs into a cigarette lighter socket... they work fine, and cost less than $20. Click HERE.

[ShutterStuff]

Nice idea, and for $5 it will save time. Right now I just grab my DMM and test at the batteries. I like pushing a button better. Just ordered mine of Ebay.

[1rosario]

Yeah, I'll have to order it. I was hoping to get it installed before we left Sunday.
At least it'll be here when we return in a few weeks!
Thank you, mikebo.

[mikebo]

I got mine from a Chinese seller off eBay, 5 bucks including shipping. Added a momentary switch from radio shack.

Mike

[1rosario]

Thanks. I was hoping someone would know where to find those. But if not, we'll Just get one of those tester types from HB.

[tenbear]

1rosario wrote:
What local store might have a digital meter?
We're leaving Sunday, too soon to order off eBay.

Thanks.

Radio Shack, Harbor Freight, Sears would have multimeters, not sure who would have the little voltmeters that you might want to install.

[1rosario]

What local store might have a digital meter?
We're leaving Sunday, too soon to order off eBay.

Thanks.

[NetBoy]

1995brave wrote:
Did anyone else notice, but the OP (NetBoy) is using a pen that states Stolen From: "the Racer's Store":)

I was wondering if anyone was going to catch that - I made sure the label on the pen was up before I too the photo. 🙂

[tenbear]

Your reading will be as exact as possible (depending on your meter) if you connect to the battery, however, (here comes the long answer) If you take it from a nearby light and that circuit is not drawing any power, (the lights and anything else on that circuit are all off) The reading will be the same as on the battery. If lights etc are on, then the resistance of the wire and the current being drawn will cause a small voltage drop. You can calculate the drop using Ohms law.

I wired mine into the circuit that powers the propane detector. The current drawn is small and is constant so that was good enough for me.

Be aware that voltmeters are not exact but are made to a certain tolerance. Depending on the accuracy of your meter you could be as much as 10% off, but probably better. IMHO, it is more important to be off by a constant amount than it is to be exact.

[full_mosey]

MyakkaTT wrote:

...
Or does it need to come directly from the battery?

1. Quick answer, yes, directly from the battery.

2. Long answer, no but.......if you have to ask, see #1. 🙂

HTH;
John

[mikebo]

I took readings at my battery and then at the leads from the exiting panel and got the same reading so I'm happy that the existing wiring gives a fairly accurate reading.

Mike

[MyakkaTT]

Question for you Elec. gurus.
Can I pull a accurate 12 volt reading form a nearby light (12 volt of course)?
Or does it need to come directly from the battery?

[mikebo]

I added mine last week.

Mike

[tenbear]

1995brave wrote:
Did anyone else notice, but the OP (NetBoy) is using a pen that states Stolen From: "the Racer's Store"

🙂

I hadn't noticed. Good catch. :B

[westend]

Nice work, guys! I'm liking ScottG's setup the most. :C

I had to go old-school and used analog meters: