Author Topic: Simple battery monitor  (Read 419 times)

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madlabs

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Simple battery monitor
« on: October 02, 2017, 08:25:42 PM »
Hi All,

Just bought a little tear drop trailer and I want to monitor its little battery. All I want to know is watt hours in and out. I don't need it to do anything fancy like learn my battery's efficiency. I just want to know how much power has gone out and how much has gone in. I'm not seeing anything like that, either cheapies that only monitor power out or much fancier models. I have the full setup for my off grid home and just don't need it for the trailer.

Thoughts? Thanks!

Jonathan

DamonHD

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Re: Simple battery monitor
« Reply #1 on: October 02, 2017, 08:36:08 PM »
I use my solar controller to monitor Wh in and out:

http://www.earth.org.uk/_off-grid-stats.html

From what is your battery being charged?

Rgds

Damon

madlabs

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Re: Simple battery monitor
« Reply #2 on: October 02, 2017, 08:54:47 PM »
Vehicle alternator for starters. I have some 100 watt solar panels that will get in the mix at some point. I just need to have some idea of how much juice is left and how much I have put back in. Doesn't need ultimate accuracy either.

DamonHD

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Re: Simple battery monitor
« Reply #3 on: October 02, 2017, 09:16:32 PM »
If you know the battery's total capacity (allowing for ageing, and the temperature for a bit more accuracy), then the battery voltage gives a decent idea of available energy.  Crudely I make an estimate based on 12.2V is 50% SoC (so effectively empty for my deep-cycle battery) and 12.7V is 100% SoC (full).

Rgds

Damon

madlabs

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Re: Simple battery monitor
« Reply #4 on: October 02, 2017, 09:25:13 PM »
I may have to try that. With my off grid home I did that in the beginning but it never seemed very accurate. It seemed like there was always power coming in and going out and that te voltage didn't help much. This is a much simpler system so maybe it is worth a shot.

Still, a simple watt hours in and out would be great.

DamonHD

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Re: Simple battery monitor
« Reply #5 on: October 02, 2017, 09:33:13 PM »
I did build a monitor for power consumption (by my RPi) based on an INA219 high-side current monitor with a suitable shunt resistor.

https://learn.adafruit.com/adafruit-ina219-current-sensor-breakout

IIRC this chip can multiply the voltage and current for you, giving you direct W, so one for charging and one for discharging, with some way to record and tally (such as an RPi), may do what you want.

You may have to be careful of voltage spikes especially on the charging side.

Rgds

Damon
« Last Edit: October 02, 2017, 09:47:00 PM by DamonHD »

madlabs

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Re: Simple battery monitor
« Reply #6 on: October 02, 2017, 10:22:51 PM »
Neat little device. I would need two I guess, one for power in and one for power out. I must admit I am looking for one I could just plug and play. The price is right though, since I have plenty of uC's and displays laying around. Still, it is another project and it seems like there should be a simple Wh in/Wh out device out there.

DamonHD

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Re: Simple battery monitor
« Reply #7 on: October 03, 2017, 12:29:45 AM »

george65

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Re: Simple battery monitor
« Reply #8 on: October 03, 2017, 06:01:51 AM »
I have been using these meters in both Ac and DC version for a bit over a year now and have had no problems.  Seem pretty accurate and work well.
have one on my solar panel output, one on my dodgy freezer seeing how much power that is Pulling ( Yikes!) and a couple spare i'm not using.
I got a household extension lead for one of the AC ones and made it so I can just plug it between the power source and the load.

They measure both ways but you could not tell what was in and out, you get a total of both ways. You would need one on the input and the output for what you are after.  They are easily re settable by pressing the button so you can monitor daily or a set period.

Look around fleabay, You will get them cheaper but this is the type you might be interested in.

http://www.ebay.com.au/itm/IT-20A-DC-Battery-LCD-Digital-Current-Voltage-Power-Energy-Meter-Multimeter-Rak-/202047128948?hash=item2f0af28574:g:u8gAAOSwfXBZp7wu



madlabs

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Re: Simple battery monitor
« Reply #9 on: October 03, 2017, 08:09:05 AM »
George, I have seen similar ones. Two of those would work, one for in and one for out. Those are a possibility. Damon, I like the look of the Victron. More than I want to spend but looks good. Dang it, I want, cheap, awesome, durable, accurate....

Thanks gents, those are some options!