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Old 08-18-2018, 03:59 PM   #1
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Battery monitor question

I recently bought the battery monitor shown below and I have a question - maybe a couple of them. And, yes I know, some folks think this quality of monitor is not worth bothering with but we work with a limited budget and this will be an improvement over the idiot lights on the main panel.

I got the meter wired up and went through the setting stage to match the AH's to my battery set. Everything seems to be working fine except... the "Charging" light doesn't come on when I have the TT plugged in to shore power. The meter shows 13.6 or so volts as soon as I connect to shore power and I've never had any issues with the charging system in the past so I assume it is working properly. Today I noticed that if I have shore power disconnected and I turn on a fan or operate any significant 12V stuff in the TT, the Charging light comes on - and then goes off as soon as I turn off the fan or whatever.

I've reviewed my wiring and I think I have everything as it should be so I thought I'd ask if anyone else has encountered this or has any ideas what might be going on. Thanks in advance for the help!
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Old 08-19-2018, 01:00 AM   #2
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I am not saying the unit is connected incorrectly. I am suggesting the current sensor is installed such that current is flowing through it opposite of the direction it was designed to flow. The reason for my thoughts is that discharge current flow is displayed as charge current flow. If battery terminal voltage increases with the converter on, current is flowing into the battery, so current flowing into the battery should illuminate the charge light. Since the charge light illuminates with current going out of the battery, the current sensor seems to have current flowing through in the wrong direction.

I donít find anything wrong measuring battery state of charge. I just find more value in adding more batteries so I donít have to be as concerned with battery state of charge.
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Old 08-19-2018, 02:38 AM   #3
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Any chance the shunt got installed backwards like I almost did on my rig recently?


PS love my el cheapo battery monitor. I get more entertainment watching the little monitor's numerical values change than watching old westerns on tv.
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Old 08-19-2018, 06:05 AM   #4
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Agree, the shunt is installed backwards. On most units this would mean reversing the small wires on the shunt. On yours it might me turning the shunt around if it came with pre-attached wires, or reversing the small shunt wires where they attach to the unit.
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Old 08-19-2018, 06:07 AM   #5
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"I don’t find anything wrong measuring battery state of charge. I just find more value in adding more batteries so I don’t have to be as concerned with battery state of charge. "

Running batts below about 50% charged shortens their life greatly.

There is no way to know the SOC with out a SOC meter, a gas gauge for the battery bank.

The usual price if a good unit is over $150 , and on up.

If this unit works it would be a big help for smaller units.

Many coaches have 500-1500 lbs of batts with about 500-1500amps of 12V available , so a 100A unit would be too small.
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Old 08-19-2018, 01:38 PM   #6
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Thanks all for the feedback. Even though I had checked my wiring twice prior to posting, the third check revealed exactly what you suggested - the sensing leads were reversed. I have switched them and now it shows charging when charging - perfect.

Regarding the sizing of the unit, our TT is relatively small and has a dual 12 volt battery set up. The power converter is a 55 amp unit so I would think the 100 amp shunt/monitor would be correct for our system. Am I wrong on that assumption?
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Old 08-19-2018, 01:44 PM   #7
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Quote:
Originally Posted by larry2c View Post
The power converter is a 55 amp unit so I would think the 100 amp shunt/monitor would be correct for our system. Am I wrong on that assumption?
The power converter might not be the issue. If you have an inverter, it can easily draw more than 100 amps, depending on what you are powering.

You should be fine...
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Old 08-19-2018, 02:29 PM   #8
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Thanks Scott - no inverter and no plans to get one any time soon
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Old 08-19-2018, 03:02 PM   #9
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I won't criticize the "el cheapo" battery monitors. Most of them work just like advertised and surprisingly, do so for a long time.

If they do what you want it to do, great. Their capabilities don't come anywhere close to the more expensive ones like a Victron, etc. but they are a quantum leap up from the OE "Led Panel".

I say that the more one expects to depend on their battery bank then go ahead and spring for a Victron BMV 712 or a similar Xantrex unit. That way you'll have what you really need and without the expense of a limited function unit that you end up replacing.

The Victron BMV 712 (or 702 with Bluetooth Dongle) provides over 60 functions. Monitoring more than just voltage and amperage but recording a history of both (min/max/duration) as well as various alarm functions (built in or relay controlled). It's especially useful for those who are using a pair of 6V batteries in series as one of those functions is "Mid Point Voltage". A useful early warning system to let you know when one of those batteries is failing.

You do get a lot of function for the higher price but if you are merely traveling from campground to campground, using batteries for a night or two on the road, go with the less expensive by all means.
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