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Old 11-19-2013, 08:38 PM   #1
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Simple & Inexpensive Battery Level Monitor?

I have searched on battery monitors and found the Trimetric and another more expensive one. But I haven't found a cheap and simple solution. I don't need a mission control level setup, I just want to be able to monitor the charge level of my two deep cycle 12V batteries during my upcoming 4-month trek. I plan to try and go 3-4 days dry camping from time to time and would like to monitor consumption.

Any inexpensive solutions that an electricity dummy like me can DIY?

Thanks,
Poppy
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Old 11-19-2013, 08:40 PM   #2
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I use and like this one: INNOVA 3721 Battery and Charging System Monitor : Amazon.com : Automotive
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Old 11-19-2013, 08:52 PM   #3
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Thanks Steve. How would you wire that? (Did I mention that I'm an electricity dummy?)

Poppy
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Old 11-19-2013, 09:56 PM   #4
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Thanks Steve. How would you wire that? (Did I mention that I'm an electricity dummy?) Poppy
Plug it into a 12volt outlet in the trailer. If the 12volt circuits are ok, you will get a really close reading.
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Old 11-19-2013, 10:14 PM   #5
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I am gonna give a vote toward the trimetric monitor. I know you want cheaper but it is an easy install and is super accurate. My favorite feature is being able to see how much amperage you are currently drawing. That way you can see exactly what certain devices take to power them...
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Old 11-19-2013, 10:20 PM   #6
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Hi, I have this same exact battery monitor in my trailer; It's plugged into the 12 volt socket in my bedroom.
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Old 11-20-2013, 04:39 AM   #7
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Thanks Steve. How would you wire that? (Did I mention that I'm an electricity dummy?)

Poppy
Yea, you just plug it into the cigarette lighter socket, and it will give you a digital readout of the battery voltage, as well as a green, yellow, and red status lights so you can see the battery condition at a glance.

Basically, you don't want to take your battery voltage below 12.0 volts.

Have you considered a solar panel? They work great in good sunny weather.
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Old 11-20-2013, 04:47 AM   #8
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Yep....KISS works for us, also plugs into the 12v power port.

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Old 11-20-2013, 04:54 AM   #9
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Basically, you don't want to draw your batteries down below 12.2 VDC (the generally accepted 50% depth of discharge, measured at 77ºF). While you can draw below this level, it will negatively effect the number of charge cycles, and thus the overall life, of your battery bank.

The Innova device will give you an estimate of your true battery voltage, but that measurement is really at the point of contact. You are, in effect, measuring the state of your 12VDC system at the 12VDC socket.

Due to the way Airstream connects the batteries to the power bus and distribution system, there will be a noticeable voltage drop from the battery terminals to the 12VDC socket, so the numbers on the gauge are simply an estimate.

If you also measure the true battery voltage at the battery with a multi-meter, you can compare that to the digital readout and get a pretty good idea of your voltage drop to that outlet and compensate accordingly.

Cheap is cheap. Nothing beats a shunt-based measuring system like the TriMetric, Magnum ME-BMK or the Blue Sky solar controllers with the IPN remote for complete and accurate battery monitoring and voltage measurement.
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Old 11-20-2013, 09:36 AM   #10
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Thanks for the input. Solar panels are planned in the near future. In the meantime I'm going with one of the cheap devices. I just bought this one from Amazon - DROK Cigarette Lighter Digital Blue LED Voltage Monitor 12 V 24V+USB Car Charger 5V/2A For IPhone/IPad/IPod - Amazon.com - that displays voltage and also has a port for charging my iPhone or iPad. I like the idea of checking the voltage directly at the battery from time to time and comparing the two.

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Old 11-20-2013, 09:57 AM   #11
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Cheap is cheap. Nothing beats a shunt-based measuring system like the TriMetric, Magnum ME-BMK or the Blue Sky solar controllers with the IPN remote for complete and accurate battery monitoring and voltage measurement.
I agree 110% with lewster. In addition to the voltage drop issue he mentions, there is this; SOC tables are based on open circuit voltage. So ideally you would read the voltage with EVERYTHING disconnected from the battery which is difficult to do. Further, for the voltage reading to be a meaningful indicator of SOC, you have to let the batteries sit for an hour or so after any charging activity to allow time for the surface charge to dissipate. A device that gives you a digital reading of the voltage at a 12v outlet is better than nothing I suppose but only barely. IMHO
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Old 11-20-2013, 10:08 AM   #12
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Quote:
Originally Posted by Birdmaestro View Post
Thanks for the input. Solar panels are planned in the near future. In the meantime I'm going with one of the cheap devices. I just bought this one from Amazon - DROK Cigarette Lighter Digital Blue LED Voltage Monitor 12 V 24V+USB Car Charger 5V/2A For IPhone/IPad/IPod - Amazon.com - that displays voltage and also has a port for charging my iPhone or iPad. I like the idea of checking the voltage directly at the battery from time to time and comparing the two. Poppy
Poppy,
If power at outlet is low then you can check at battery. The voltage won't be greater at outlet.
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Old 11-20-2013, 10:16 AM   #13
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Most of my camping is boondocking,even with a 50 watt solar system my wife could kill the batteries in 2 days.Now at 200 watts we get by pretty good.I don't see getting 4 days out of batteries unless you are very frugal with power useage
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Old 11-20-2013, 10:24 AM   #14
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Quote:
Originally Posted by Birdmaestro View Post
Thanks for the input. Solar panels are planned in the near future. In the meantime I'm going with one of the cheap devices. I just bought this one from Amazon - DROK Cigarette Lighter Digital Blue LED Voltage Monitor 12 V 24V+USB Car Charger 5V/2A For IPhone/IPad/IPod - Amazon.com - that displays voltage and also has a port for charging my iPhone or iPad. I like the idea of checking the voltage directly at the battery from time to time and comparing the two.

Poppy
Poppy,

We tink alike...

I just bought two of these.

One to keep track of the 6v in the Ford. (mounted in a box w/on/off switch)

The other will get put in the glove box of the boat.

POI...these are within .1-.2v on my Fluke VO. I would think yours would be comparable. Take a reading at the batt's for a baseline to compare with the power port.

Bob
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Old 11-20-2013, 02:50 PM   #15
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Hi, there is the possibility that my battery monitor won't read exactly the same as my Fluke meter. Without a load on the system, I don't believe that there would, could, should, or will be any difference in the 12 volt reading at the battery or any other place on my trailer. To be actually different there has to be a load, short, poor hot, or poor ground connection. Your 12 Volt battery/ies aren't trying to start an engine. There is no major load on your 12 Volt system in your trailer.
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Old 11-20-2013, 03:30 PM   #16
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Hi Birdmaestro:

The cigarette lighter voltage meter method mentioned here is easy, cheap and works great.

(A little off topic, but I believe it relates). Years ago I temporarily put an amp hour meter between the battery and the 12 volt fuse box. I turned on one 12 volt item at a time and wrote down how much each item was drawing from the battery. I posted the list inside a cabinet and used it to estimate how much was being taken from the battery. Not perfect, but it works for me. -- Enjoy!
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Old 11-20-2013, 03:46 PM   #17
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Thumbs up meter not load...

The difference for me is in the $39.00 Volt-Minder & $11.00 Druk.
I just note that both cheep meters are consistently low.

Bob
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