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Old 05-12-2014, 04:14 AM   #1
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Default Juice meter

Just returned from a 4 day spring trip today and had a perfect, awesome, great, (many other words) trip. Stayed at local lake about 80 miles away, not a campground, but a large parking area with a few other folks around. Didn't run the generator at all and only turned on the heater a short time in the mornings, the temps were in the low 30's so it was really nice, maybe a total of 15 min. for lights, as the days are pretty long right now. We also ran the pump as needed for dishes, showers and toilet. So... after about 3 days I wondered how much juice was left in my batteries. I have decided I need a wall mounted juice meter! I do not want to open the battery box and slide out the batts to put a hand held meter on them to check juice anymore, so what kind of wall mounted juice meter do I need? I have sensory overload looking things up the computer and I just want someone to tell me to get "this" one. I do sort of maybe kinda vaguely pretty sure know about solar use and amp hour stuff but am looking for just the juice meter for now. By the way, my generator works fine, I just hate the little buzzard when I'm camping. I will probably get about 200 replies and am looking forward to them all, bring em on!
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Old 05-12-2014, 10:34 AM   #2
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Default Re: Juice meter

Here is what I installed. It works great.

http://www.jamestowndistributors.com/us ... ry+Monitor
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Old 05-12-2014, 10:48 AM   #3
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Default Re: Juice meter

That is nice

For bare minimum info a volt meter with an on / off switch would give you an idea of what is going on. I don't have a specific model to recommend like you asked for sorry. Another idea is to use an inverter that displays volts. That's what I do. I turn the inverter on to check volts then off again if not needed.
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Old 05-12-2014, 12:49 PM   #4
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Default Re: Juice meter

We have a Trimetric meter which works fine. I think Xantrex makes a similar one. You have to install a shunt in the negative battery line for them. Pretty easy for one battery, tougher if you have two that are a ways apart like ours are.

I was in the process of testing an alternate method, when I found out I needed all the new charging stuff (funny how that works). The resting voltage of the batteries is a good indication of the state of charge of the batteries, but a PITA to use because they need to sit with no load for an hour our more before checking them. From what I have read, if you have a moderate, known, load the batteries when you check them, it is also accurate but you don't have the wait time. You do need to make a chart of your battery's state of charge vs voltage with the load on it, but that is not a huge job. You then just need a voltmeter and switch on load to tell what your state of charge is (with everything else off). We have quite a bit of battery at 375AH, and we found a 5 amp load dropped us about .1 volts off the standard state of charge vs resting voltage chart. I will be looking the this again in the near future, as the Trimetric can't keep track of the batteries separately, but I can get the voltage from each separately, and load the separately. My guess is that it well may be more accurate than the Trimetric at times, especially during cycles of short charges off the solar, where you don't get completely full every day.
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Old 05-12-2014, 02:46 PM   #5
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Default Re: Juice meter

Quote:
Originally Posted by booster
We have a Trimetric meter which works fine. I think Xantrex makes a similar one. You have to install a shunt in the negative battery line for them. Pretty easy for one battery, tougher if you have two that are a ways apart like ours are.

I was in the process of testing an alternate method, when I found out I needed all the new charging stuff (funny how that works). The resting voltage of the batteries is a good indication of the state of charge of the batteries, but a PITA to use because they need to sit with no load for an hour our more before checking them. From what I have read, if you have a moderate, known, load the batteries when you check them, it is also accurate but you don't have the wait time. You do need to make a chart of your battery's state of charge vs voltage with the load on it, but that is not a huge job. You then just need a voltmeter and switch on load to tell what your state of charge is (with everything else off). We have quite a bit of battery at 375AH, and we found a 5 amp load dropped us about .1 volts off the standard state of charge vs resting voltage chart. I will be looking the this again in the near future, as the Trimetric can't keep track of the batteries separately, but I can get the voltage from each separately, and load the separately. My guess is that it well may be more accurate than the Trimetric at times, especially during cycles of short charges off the solar, where you don't get completely full every day.
Hi AK49er,

I agree with Booster that the Trimetric is what you need. Although his other points are well founded, they are somewhat complicated, and I'll chime in and say if you just run it the way it the way it comes (with a few minutes spent telling it what amp-hours you have, etc., per their instructions), the reading you get won't be all that bad as long as you are willing to take some error (maybe 10-15% [Booster: please correct me if I'm way off base here]). BTW, this is how I run my Trimetric on a single battery bank consisting of four six-volt batteries, and it is "close enough" so far for my purposes.

Hi Booster,

This might be the wrong thread to put this in, but since you mentioned the Trimetric and your somewhat complex battery charging/solar system, I'll offer up this: Since you also have "bank switches", couldn't you have separate shunts on your banks, and have a multi-position switch at the Trimetric? Then you could be using say bank one, and having bank two "resting", and monitor bank two with the Trimetric to get the kind of accuracy you're striving for. The fly-in-the-ointment here is you might have to reset the Trimetric each time you switch banks. (Heck, you could get multiple Trimetric's.) Not trying to tell you that you're doing anything wrong with your system as you're way ahead of me (and most others) on this whole topic!

Regards, Dick
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Old 05-12-2014, 04:55 PM   #6
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Default Re: Juice meter

Quote:
Originally Posted by dicktill
Hi AK49er,

I agree with Booster that the Trimetric is what you need. Although his other points are well founded, they are somewhat complicated, and I'll chime in and say if you just run it the way it the way it comes (with a few minutes spent telling it what amp-hours you have, etc., per their instructions), the reading you get won't be all that bad as long as you are willing to take some error (maybe 10-15% [Booster: please correct me if I'm way off base here]). BTW, this is how I run my Trimetric on a single battery bank consisting of four six-volt batteries, and it is "close enough" so far for my purposes.

Hi Booster,

This might be the wrong thread to put this in, but since you mentioned the Trimetric and your somewhat complex battery charging/solar system, I'll offer up this: Since you also have "bank switches", couldn't you have separate shunts on your banks, and have a multi-position switch at the Trimetric? Then you could be using say bank one, and having bank two "resting", and monitor bank two with the Trimetric to get the kind of accuracy you're striving for. The fly-in-the-ointment here is you might have to reset the Trimetric each time you switch banks. (Heck, you could get multiple Trimetric's.) Not trying to tell you that you're doing anything wrong with your system as you're way ahead of me (and most others) on this whole topic!

Regards, Dick
Hi Dick, I think your 10-15% is probably a pretty good range for the Trimetric when it is used in the "normal" way, and the batteries get full on almost every charge cycle. Where the error seems to multiply is if you have repeated "short" charging cycles, like with solar, or if you don't drive far enough to get totally full. If you don't get full, the Trimetric doesn't reset to 100%, which is the calibration point. The discharging accuracy is pretty accurate, but the charging side is dependent on the "charging efficiency %" that you program in. If you get that percent just right, I think you can even be within your 10-15% on multiple short cycles. Also remember that if you discharge slowly (under the 20 hr rating AH) you will have more AH available, and the Trimetric % will read low. If you don't run the batteries really low, the 10-15% should cover that error, but if you read 50% (normal recharge point), and it is really 65%, that is a pretty large error. If you are always at the low discharge rate, you fudge the accuracy by telling the Trimetric you have more battery AH capacity that the 20 hr rating.

I did look at putting in a second Trimetric with the new system, which would have bee really cool and handy, but it turned out that lack of real estate put an end to that. I would have had to add the second shunt, which wouldn't have been too bad, but it would have also made me isolate each of the battery negatives, and add cables I didn't have room for. Too bad.

We do plan on using the Trimetric we have pretty much as you describe. Because we have mismatch battery banks, it is best if we don't discharge both at the same time, unless we need the added capacity to run something. We can run on one bank until it gets low, and then switch to the other, and reset the Trimetric. This also lets the solar work on less battery capacity and be more likely to always get it full. I envy your identical batteries, as you have none of these issues.

My, yet uproven, guess, is that the voltage check under moderate load will turn out to be quickest, easiest, and most accurate way to check state of charge. With the Trimetric we can see voltage and amperage which makes setup easy. The 5 amp area works fine and is non-critical, as long as it is consistent. I think we will just need to turn on the same things each test, like the fluorescent lights, check the voltage, and be done. At worst it will be a good double check on the Trimetric numbers.
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Old 05-13-2014, 01:06 AM   #7
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Default Re: Juice meter

I have a lot less capacity than Booster, and when I enable my batteries, I only have a smallish draw from my propane and CO detectors to hopefully stabilize my 2 batteries from the surface charge issue, and so I just use one of these to get a very general state of charge.
http://www.walmart.com/ip/Equus-Innova- ... r/15137663
I think it's accurate enough for my purposes, and it usually macthes my idiot lights on th emonitor panel. It quantifies the voltage into a 12VDC number, where the monitor panel just tells me what color my power happens to be when I push the test button. Green power is best, I think.
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Old 05-13-2014, 01:10 AM   #8
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Default Re: Juice meter

Hi Marko, Which inverter do you have that also displays volts?
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Old 05-13-2014, 01:28 PM   #9
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Default Re: Juice meter

This one: http://www.classbforum.com/phpBB2/vi...hp?f=10&t=2082
I haven't pushed the replacement to the max after the first one starting smoking!

If doing it again, still on a budget, I'd go with one of these: http://www.bestconverter.com/Prowatt-SW_c_150.html I've placed a few orders with Best Converter over the past few years.

Do you have a 12v outlet that is connected to the house battery? If so, you should be able to find a plug in type volt meter at an auto parts store. That would be good for occasional use. It would be useful to know voltage output from alternator, voltage output from converter etc., and it would give you an idea when you'd need to run the generator or engine to charge the battery when dry camping.

If you go with one of the full featured meters mentioned in this topic then mount it somewhere easily visible. I put some meters that show amps in/out volts etc. in a closet because it was an easier installation but I rarely look at them, almost never. That's why I look at the inverter display for volts.
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Old 05-13-2014, 01:55 PM   #10
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Default Re: Juice meter

I am glad you got to talking about the inverter showing the voltage, as it reminded me about ours. Ours also show the voltage, and has a power bar for the output, but the voltage reads about .2 volts lower than the Trimetric. I checked the voltage at the imput to the inverter and it was the same as the Trimetric. It probably isn't a big deal, but if it got it to low voltage cutoff early, it might not be good. Time for me to contact Samlex, or Randy at Best Converter.

I agree with Marko, if you have a 12v accessory outlet that runs off the coach battery, the plug in meters work well, especially the one in the link someone put up as it goes 2 decimal places. It was all we used before the Trimetric and it worked very well.
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