Thoughts on this battery meter

Hi BurbMan,
That bar-graph display is not a particularly useful "battery monitor", although having a digital volt-meter most certainly can be handy at times! So, if that particular display appeals to you, and you don't mind having only one decimal place of resolution, and you don't need to know the SOC, then there's nothing wrong with that meter… Go for it!

I purchased the same volt/ammeter that Rich (RJsfishin) has from an ebay seller named "haruyr_kb" ('cept I chose a 100A shunt) for $11. I installed it in the dashboard of my truck so that I can monitor voltage and current from my alternator to the house battery bank. I was able to calibrate the voltage display (using a Fluke DVM) and it has proven to be quite accurate. It is nice to know what's happening, but this type of ammeter is one-way only (positive Amps,but not negative Amps). Again, useful info… but not a battery monitor.


In my TC I have a TriMetric battery monitor because (like mena661), SOC and how many (theoretical) Amp-hours I have left until charged or discharged is the most important data to me. But a TriMetric is quite a bit more expensive than a basic digital voltmeter and I acknowledge that not everybody wants/needs that level of battery monitoring.

Happy tinkering!
-Mark

mena661 wrote:

BFL13 wrote:
But you can get by without the AH counter; you can't get by without the voltmeter.

I disagree. I don't use the volts display, I'm only concerned with amps drawn and amp hours removed. I know about how much I can use and if it's more than that I go looking for the problem (like when I left the basement lights on all night). I have no idea what a particular voltage reading tells me unless the batts were REALLY low for that particular day of camping. If it was a tenth or two off that wouldn't tell me anything. Yes, I've seen the SOC charts but I still look at Ah removed cause that tells me how much I've used vs how much more I can use.

That's just because you have so much battery bank that your voltmeter would have to read to fourteen decimal places to indicate any drop in SOC between Friday and getting home Tuesday after a long weekend. :)

I sent Lin an email last night, a long, long, email, describing the need for a comprehensive TWO CHANNEL ampere hour and watt hour meter. Switchable displays. LCD and LED. Vamos a ver.

BFL13 wrote:
But you can get by without the AH counter; you can't get by without the voltmeter.

I disagree. I don't use the volts display, I'm only concerned with amps drawn and amp hours removed. I know about how much I can use and if it's more than that I go looking for the problem (like when I left the basement lights on all night). I have no idea what a particular voltage reading tells me unless the batts were REALLY low for that particular day of camping. If it was a tenth or two off that wouldn't tell me anything. Yes, I've seen the SOC charts but I still look at Ah removed cause that tells me how much I've used vs how much more I can use.

BurbMan wrote:
Summer is for camping, winter is for tinkering....the list is already building LOL

You could have (still can) installed the combo meter like below,
a 50 amp w/ shunt for $8-$10 ebay.
Once you get used to using these 2 meters, there isn't much they won't tell you.

Summer is for camping, winter is for tinkering....the list is already building LOL

My two battery monitor meters jump around some during the one day/night run off the battery based on what is on at the time. Since both battery battery banks are selected both meters read the same DC VOLTS. With my BLUE SEA Battery switch setup however I can isolate the two battery banks or even just look at any battery mounted on the trailer tongue. I usually switch to either one bank or the other on occasion to see how each battery bank is doing. This lets the switched out battery bank go to its rest voltage pretty quick.

Like said above this only gives me approximately state of charge and I have been doing this since 2009 on these GP24 Interstate 12VDC batteries and all still going good.

This is how my GP24 12VDC batteries are wired up.


Roy Ken

BurbMan wrote:
BFL, thanks for the practical application of this...that's exactly how I use my voltmeter today and it works pretty well for what I need. Having the graphic readout that approximates SOC I thought would be useful (and cool) but not sure how accurate it is vs. the old reliable chart posted by Roy B. I may have to buy one and post a review....

You have seasonal gizmoitus! It happens to us all :(

BFL, thanks for the practical application of this...that's exactly how I use my voltmeter today and it works pretty well for what I need. Having the graphic readout that approximates SOC I thought would be useful (and cool) but not sure how accurate it is vs. the old reliable chart posted by Roy B. I may have to buy one and post a review....

"Measuring voltage can be relatively accurate only after a couple of hours with out input or current drain."

Technically correct, but not applicable to camping when the accuracy needed is just to be able to decide if it is time to do a recharge or not.

I find the voltage comes back quickly in a couple of minutes (not hours) to what passes for "resting" while camping, except if solar is on during the day, when the surface charge takes so long to dissipate if you turn off the solar.

If it is showing 12.3 with nothing running and the furnace comes on so it says 11.9 or whatever, and the furnace goes off, it only takes a minute to go back to 12.3. That 12.3 is a good marker for what is going on.

The morning voltage is most useful to get your daily usage so you can predict when the next recharge will be. Say it drops by 0.2 each day. Starts from home at full 12.7 then 12.5, 12.3, so you know next morning it will be 12.1 and that is your time to do another 50-90. (if you have Wet 6s where 12.1 is 50%--wet 12s its 12.2) It doesn't matter if it is 0.1v out of whack. Who cares if it is really 12.2 or 12.4 instead of 12.3?

But you plan to go sight-seeing tomorrow, so no chance to sit there with the generator running for a couple hours, so you decide to do the recharge today. You don't want to go an extra day and let it get down to 11.9.

So camping is not a science lab and the voltmeter is accurate enough for what you want it for. An AH counter is also a good tool, especially when you can compare that count with your morning voltage to see if they "agree" (if they don't you can go looking for what's wrong) But you can get by without the AH counter; you can't get by without the voltmeter.