What is the best affordable electronic battery monitoring system

[Paul Elliott]

Rick and EngNate, thank you!

Vasco/Rick I,
I just re-read your message, and it sounds like you and I have different problems. Your monitor jumps to 0AH when you stop charging, and mine jumps to 0AH during charging. Rick described the situation I've got, and EngNate's explanation seems to fit your symptoms.

Somehow, I had the idea that the monitor was able to "learn" the characteristics of the battery bank. Perhaps not, and I will dig into the manual again. Regardless, it sounds like I will be doing some tweaking of the parameters.

[Zach]

So out of curiosity... what math do these things do to compute amp hours and all the rest? Knowing the overall capacity of the battery bank, could a note card with voltage and their amp hour or % equivelants be listed... do the same job?

Seems like all they can read is voltage in the battery, any long hand that turns that into something meaningful?

[Rick]

Please read a parallel thread in this batteries section regarding "maxing out battery" where there is a contribution regarding the futility of using voltage measurment as a "look-up" table to indicate capacity. The overwhelming problem with a voltage based measurement system is that not only can it not give validity to state of charge it is light-years away from ANY indication of state of capacity.

"Real" battery monitors measure voltage and current simultaneously along with time "marks". Temperature is also desirable yet may be manually entered as long as no more than 10 degrees F is in error. Less is better, of course.

This basic input data is only the beginning and must be very stable and accurate over years, not just minutes. There are many algorithms which constitute an overall schema to evaluate the state of charge and energy consumption/distribution and other factors. The most useful "output", though, for most users who just don't give-a-darn about the technical aspects, is a "fuel guage" to indicat just when to start or stop charging.

Think about it. Who really cares just what is an Amp-hour (most cruisers can only call it "Amps" without differentiating between current and current times time and geeze what a difference!). What most of us REALLY care about is how much longer can we continue to use the energy at the present rate of consumption, or, even more simply, "I don't care just deliver the power"! "Can I turn off the generator now?"

You don't see automatic generator start/stop devices on cruising boats because it just is not safe to operate that way as it can be with a recreational vehicle. Who wants to sink their boat automatically because an unmonitored exhaust hose is leaking cooling water into the bilge?

Next?

[CSY Man]

So out of curiosity... what math do these things do to compute amp hours and all the rest? Knowing the overall capacity of the battery bank, could a note card with voltage and their amp hour or % equivelants be listed... do the same job?

Seems like all they can read is voltage in the battery, any long hand that turns that into something meaningful?

Yeah, I was there a few years ago:

I used my analog volt meter to "calculate" how far up or down I was as far as the house bank capacity.

The good book says to not go below 50 % as that would shorten the life of yer battery.
50 % was right around 12.4 volts if memory serves right...?
I used 75 % instead: 12.6 volts, a good and fat safety margin due to the crude measuring method.

(The above numbers came from Calders book, my bible, as well as the co-bible written by the Dashew's)

Cruised around like that for 6 years on present boat and was fat, dumb and happy.
The numbers worked, no problems noted.

2 years ago a friend donated one of them battery monitor gizzmos to my boat.
I did not think I needed one, but installed it anyway, with the optional temp sensor.

Got a wake up call on how in-accurate the analog voltage system really was. Also woke up to how much power I really consumed in a day.

With solar panels these electronic gizzmos becomes really useful as you can see exactly how much is going in and how much is going out.

If ya are sitting at the dock all the time with shore power plugged in 24/7, no need for a battery monitor.
If not, they are quite useful.

DH...Former purist...

[FreeSail]

The electric side of things, is an area, I am very weak in. So take the question for what it is. If your using a OutBack MX60 MPPT Charge Controller do you also need a link 1000 battery monitor ?