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Old 08-06-2019, 05:17 PM   #1
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Newbie battery monitor question

Newly retired, we now hope to travel for much longer periods of time. We have upgraded from a popup to a FR 21FBRS and just love the floor plan. We prefer state and national parks which often do not have electric hookups. Anticipating some longer periods without shore power, we have purchased a Honda EU2200i generator and 2 COSTCO 6V golf batteries. While mountain/forest camping, our electric needs can be minimal- no AC, maybe a 12v fan, fridge set to auto, a few lights to read at night, showers in the bathhouse and we may occasionally need to use the propane heater. My question is what is the simplest, least complicated battery monitor for our needs? I just want to make sure that the battery charge does not drop below 50% and to know when to turn off the generator when the batteries are at 100%. I understand that the Victron and the Trimetic monitors are preferred, but is there something simpler or cheaper that will fill our needs?
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Old 08-06-2019, 05:26 PM   #2
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I know those that are really serious about their RV 12v systems will scoff at this, but I use this multi-meter from Harbor Freight most of the time. And with a coupon you can get it for free
https://www.harborfreight.com/7-Func...ter-63759.html
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Old 08-07-2019, 09:10 AM   #3
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Like Scott, I'd suggest a multimeter. In addition, add a hydrometer (to measure the specific gravity of the cells - I use THIS one) and a good temperature-compensated state-of-charge table. I've used the one below:


Note: "Open Circuit Voltage Reading" is based on measuring the battery voltage after being disconnected from any loads for ~4-hours.
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Old 08-07-2019, 09:38 AM   #4
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For 3 years I used nothing to monitor the battery other than the indicators installed in my Surveyor. A month or so ago after a similar post by me, NMWildcat recommended the same multimeter from harbor freight which I did pick up (free).

Have used it on 3 trips now to monitor battery level. When comparing the meter to the indicators I have found that they do agree with each other. The indicators dont give exact readings obviously. So I kidna watch the incicators and then occasionallly check with the meter thur the day when I know I might be running low. Not bashful about running my quiet 2000W generator a couple of 2 hour sessions per day.

This is a step up in monitoring from the past for me and is easy and not inconvenient for me as I am always tinkering around at the CG anyway. Sure there are more convenient methods and systems for those that want automatic and spend the $$$.

Personally not a gadget man.... Too cheep!
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Old 08-07-2019, 09:46 AM   #5
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Far be it for me to recommend that someone NOT have a multimeter. However, you are going to need not only voltage but current as well in order to determine when to shut down your generator. Measuring voltage doesn't work, especially when you are actually charging the battery! In my case I run the generator until the charge current drops below say 12 or 15 amps. After that it isn't worth it. (you will never get to 100% SOC with a generator, takes at least 24 hours to get the last 10 or 15 percent) While Trimetric or Victron work well, you can get a much cheaper unit from Amazon that will meet your needs. https://www.amazon.com/AiLi-Battery-...ustomerReviews
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Old 08-07-2019, 09:47 AM   #6
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My solution.

Amazon, BM2 was $40.

Simple connection in the fuse panel. 5 minutes or less. Red and black wire.

The device is simple. Monitors voltage 24/7 and keeps records of it, I.e. a graph.

Transmits to your phone.

It also alarms when voltage goes down. Does not monitor amperage! That is a thing for big usage devices. I am an engineer thus do not need it.
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Old 08-07-2019, 09:55 AM   #7
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It also alarms when voltage goes down. Does not monitor amperage! That is a thing for big usage devices. I am an engineer thus do not need it.
Neat, Bluetooth has made for really inexpensive devices.

However, the OP wants to know when to shut down his generator while charging. The BM2 will only show the converter voltage during that process (at least 13.4) which is off the scale of a battery voltage/SOC curve, just like that 4th LED on the battery monitor panel, which doesn't mean 100% only means "charging."
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Old 08-07-2019, 09:59 AM   #8
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Far be it for me to recommend that someone NOT have a multimeter. However, you are going to need not only voltage but current as well in order to determine when to shut down your generator. Measuring voltage doesn't work, especially when you are actually charging the battery! In my case I run the generator until the charge current drops below say 12 or 15 amps. After that it isn't worth it. (you will never get to 100% SOC with a generator, takes at least 24 hours to get the last 10 or 15 percent) While Trimetric or Victron work well, you can get a much cheaper unit from Amazon that will meet your needs. https://www.amazon.com/AiLi-Battery-...ustomerReviews
Have not gotten so concerned (yet) with when to turn Geny off. Found that in general 2 hours 2x per day and then when I know I am running something that is a big draw occasionally, keeps me abofe the 50% charge level at my usage.
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Old 08-07-2019, 10:29 AM   #9
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If you own the BM2 you will learn the when.

As stated. Two hours is a great plan. With the BM2 you will learn that you have to run the Generator 2-3 hours to get near 90%. Then trickle charge another 24 for a full charge.

Have to learn about surface charge etc.

We really like ours. The graph thing really taught me a lot.

You will see the results of Using the hydraulics, slides, generator, car alternator. Educated me a lot.

I also have lp Bluetooth gages.
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Old 08-07-2019, 02:36 PM   #10
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My 2 hrs generator use 2x per day is in the case of 1, 12 V battery D Cell.

With the 2 6V you might find that you dont neeed as much or as often. I just think it works for me and rather overdo it on the charging a bit. Running in AM and evening works for me, needed or not.
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Old 08-07-2019, 05:23 PM   #11
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There's plenty cheaper but not for your needs. Suggest Victron model bmv702 as cheapest full function accurate monitor. Easy 3 wire plug &play install.
Oh...and it takes a MINIMUM of 6 hours to get back to 100% from 50% on wet cells regardless of bank size and charger size. A real battery monitor will prove this to you.
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Old 08-07-2019, 06:13 PM   #12
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There's plenty cheaper but not for your needs. Suggest Victron model bmv702 as cheapest full function accurate monitor. Easy 3 wire plug &play install.
Oh...and it takes a MINIMUM of 6 hours to get back to 100% from 50% on wet cells regardless of bank size and charger size. A real battery monitor will prove this to you.
I agree. You have to have amperage and integrated charge and SOC. Victron is nice, Amazon has cheaper. Voltmeter by itself is really not that good...but others disagree.
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Old 08-08-2019, 07:34 AM   #13
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Jared Gillis (All About RVs) has a good YouTube video discussing three different battery monitors all under $40.

https://youtu.be/tObHbsSDWeQ
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Old 08-08-2019, 07:38 AM   #14
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If you are looking for something easy to use and low cost, you can use something like this. There are several manufacturers out there. https://hobbyking.com/en_us/turnigy-...-analyzer.html
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Old 08-08-2019, 07:55 AM   #15
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If you are looking for something easy to use and low cost, you can use something like this. There are several manufacturers out there. https://hobbyking.com/en_us/turnigy-...-analyzer.html
While that would work, I wouldn't want to put my entire DC system in series through something like that. If it fails...all stops. Better to get something that has a heavy duty external shunt or at least a separate shunt connection. Doesn't have to be expensive as there are many choices for less than $50.
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Old 08-08-2019, 07:08 PM   #16
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Coincidentally I have a BM2 coming from Amazon. Might go with a more expensive one later. It was only 30 bucks on Amazon. I can always put it in my old truck if I upgrade.
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Old 08-09-2019, 08:43 AM   #17
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Cheap

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Originally Posted by NMWildcat View Post
I know those that are really serious about their RV 12v systems will scoff at this, but I use this multi-meter from Harbor Freight most of the time. And with a coupon you can get it for free
https://www.harborfreight.com/7-Func...ter-63759.html
I purchased online a $2.00 digital volt meter. Reads voltage to two decimal places. Works for me.
Cut hole in range hood to mount it and tied into hot side of light wiring.
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Old 08-09-2019, 09:30 AM   #18
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I purchased online a $2.00 digital volt meter. Reads voltage to two decimal places. Works for me.
Cut hole in range hood to mount it and tied into hot side of light wiring.
I bought a pack of 5 volt meter modules for 11.00 and mounted one in side of the bench seat. Easy to see for everyone.
Keep your batteries in the 50-90% range when camping and blast them back up to 100% when plugged in.
Running your generator twice a day will keep your battery in the sweet spot without trying to charge past that 90%+ area where you are just burning gas and charging very slowly.
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Old 08-19-2019, 06:57 PM   #19
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I use one of these. Got it on sale for 20 bucks
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Old 08-19-2019, 07:27 PM   #20
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OP is looking to go boondocking regularly. IMO, a proper battery monitor would be a better solution than just a multimeter.
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