Teardrops & Tiny Travel Trailers

[bdosborn]

Here's a chart to show your battery condition by voltage. I like this one because it has multiple temperatures shown:



Bruce
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2009 6.5'X11' TTT - Boxcar
Custom Frame, Poptop, AC, Espar Diesel Furnace, HW Heater, Sink, Shower, 12V-120V, LED Lights, TV and XM Radio, DVD Player, 220W Solar Panel, PD 9130 Charger, Tongue Box, Filon Exterior, 1000W Generator, Patient Wife
Boxcar Build Thread

[GHOSTSSX]

Sticky??

[mikeschn]

If someone adds the red, yellow and green chart, this will become a sticky!

Mike...
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The quality is remembered long after the price is forgotten, so build your teardrop with the best materials...

[48Rob]

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[mikeschn]

Thanks Rob...

It's sticky now!

Mike...
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The quality is remembered long after the price is forgotten, so build your teardrop with the best materials...

[angib]

My experience and understanding of using battery voltage to estimate state of charge is:
- different battery types give different results;
- if the battery is being used (eg, discharged), the voltage changes (drops);
- most voltmeters are of limited accuracy.

I think the charts above are for traditional flooded lead-acid batteries - so they don't apply to gel/AGM or higher tech batteries.

My conclusion is that you need to calibrate your voltmeter and your battery so that you can work out that, for you, an indicated 12.4v means 'fully charged' and 11.8v means 'pretty empty', or whatever.

I don't believe you can be more accurate than this.

Andrew

[bdosborn]

Andrew,

Good point on the accuracy of the chart, it's at best a "wet finger in the wind" method of estimating remaining capacity. A digital voltmeter should have sufficient accuracy, it's the uncertainty introduced by the voltage versus load characteristics you mentioned that makes it difficult to read the battery's charge state from a voltmeter as well as differences from battery to battery. Ideally, the battery should be measured after 24 hours of no load, which isn't very practicle when its 11:00 p.m. on the third night of camping and you're wondering if you should turn the lights off. However, measuring after 5 minutes of no load will give you a good idea of where you're at with the chart being a general guide. I did a brief internet search on the chart and I believe it's applicable to all battery types including AGM and gel but I've been wrong before...
Bruce
_________________
2009 6.5'X11' TTT - Boxcar
Custom Frame, Poptop, AC, Espar Diesel Furnace, HW Heater, Sink, Shower, 12V-120V, LED Lights, TV and XM Radio, DVD Player, 220W Solar Panel, PD 9130 Charger, Tongue Box, Filon Exterior, 1000W Generator, Patient Wife
Boxcar Build Thread

[asianflava]

[mikeschn]

Don't they make some kind of a computerized gage that tracks your usage, and lets you know remaining battery life based on usage? And if I recall it wasn't cheap. $200 to $300 for one silly looking little round gage.

Mike...
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The quality is remembered long after the price is forgotten, so build your teardrop with the best materials...

[bdosborn]

Mike,
I think this is what you're talking about.


It tracks amp-hours so its supposed to be pretty accurate. But yeah, its spendy.
Linky
Bruce
_________________
2009 6.5'X11' TTT - Boxcar
Custom Frame, Poptop, AC, Espar Diesel Furnace, HW Heater, Sink, Shower, 12V-120V, LED Lights, TV and XM Radio, DVD Player, 220W Solar Panel, PD 9130 Charger, Tongue Box, Filon Exterior, 1000W Generator, Patient Wife
Boxcar Build Thread

[angib]

I'm not sure how 'different' the battery has to be before its state-of-charge/voltage differs from flooded lead-acid - AGMs may be similar enough. I can be wronger than Bruce without difficulty.......

The one point to make about digital voltmeters for the novice is that there is a big difference between resolution and accuracy. Cheap meters may read in steps of 0.01v, but may only be accurate to +/-0.1v - some people assume that because the display looks accurate, it is accurate, but we are into free lunch territory here!

Andrew

[cracker39]

I know that this has been discussed before, but my memory's not the best. Are the readings on these charts for under load or no load? My battery is a standard deep cycle from WM. Right now, it is about 70 degrees outside and the temp in the battery box could be between 65 and 70 degrees. My digital battery meter I have plugged into a socket inside the camper is reading 13.6 volts. I've had the shore cable plugged into a 30 amp 110VAC outlet for a couple of weeks.

My no load reading is ABOUT 1.0 volt below the number on the chart for 70 degrees and 100% charge (i.e., 12.562). Nearly every auto or deep cycle battery I've owned neasured over 13 volts when fully charged.

Regardless of the answer, I'd use this chart to measure an at-rest battery's state of charge. It's better to err on the side of caution rather than let it get too low before re-charging.
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Dale

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[Alphacarina]

[hurricaner]

That first chart is not correct. The voltages do not vary any where near that much. Here is a correct one .
http://jgdarden.com/batteryfaq/carfaq4.htm