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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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Quote:
Originally Posted by tomkatb View Post
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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Quote:
Originally Posted by ScottBrownstein View Post
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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