Battery monitor: useful tool or toy?

[Ductape]

Hello all. As we prepare for FT (mostly boondocking) I am working through the 12v upgrades. Got the 600 AH of Lifelines in place. Two banks of 6v pairs; 4 batts in all. Upgraded the converter to 80, probably change out the inverter later to an invert/charge unit as well. Will top it off with solar in the end.

Question I have is an AH monitor e.g. Trimetric seriously useful, or is a voltage check just as accurate (more accurate?) an indicator of SOC? Mainly interested in what will I really need to measure to make decisions on when to fire up the gen vs let the solar fill the bank.

Thanks again. I've spent a lot of my career working with tech but I am learning a lot from you guys.

[Snowman9000]

On a budget, a person could try something like this. $36 on ebay. For some reason this listing is priced in Aussie dolllars on the US ebay site. The one priced in USD is a few bucks more. I bought from this listing. Just got it today, so I can't tell you how good it is. But people on the internet have liked it for various charging applications. It has a 100A shunt.

http://www.ebay.com/itm/181137155880?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[MEXICOWANDERER]

I wish I had that gift...

:h

[tenbear]

I have a voltmeter and an ammeter. The voltmeter tells me when I should recharge and the ammeter tells me when the battery is sufficiently charged.

[joelmyer]

I can't imagine dry camping without something like the Trimetric.

Last winter I collected amp hour usage data to decide how much solar to install. This winter I will use it to manage generator time.

That said, there's 200-300 of us military retirees dry camping for the winter down at Trumbo Point. I'm the only one I know of that has a Trimetric. Most don't even have voltmeters, the ones that do with solar think all is well when they see 12.6+ when the sun has been up a while.

The ones without solar run their generators a lot. In either case when the lights don't work in the morning before generator or sun hours, they go pick up a new battery. That works too I guess.

I guess you could manage reasonably well looking at voltage after sunset and before evening power usage and morning voltage before sunrise and adjusting generator time to make those happy numbers.

I managed a few winters before Trimetric. Start generator when Charge Wizard light went solid on, stop when you could hear generator speed when you turned a light on.

Joel

[NinerBikes]

Ductape wrote:

NinerBikes wrote:

smkettner wrote:
I would get solar before the monitor.

I would agree with this. And if you get a little RC charger monitor with an amp meter hooked up in line while charging, with a little practice, your solar panels output capacity versus the voltage and amps the batteries are taking in will give you a really good handle on the State of Charge of your batteries.

If your solar panels are capable of 25 Amps, and your batteries are taking 14.3 -14.4V but only accepting 5 amps or less, you are pretty much topped off on charge on your batteries. The scenario changes a bit as fall and winter approach and the days get shorter, generator time might need to make up a bit early in the day when the batteries state of charge is lowest, then let the solar panel do the top off charging the rest of the sunny day.

This kind of what I was thinking. I can sort of read SOC crudely now by watching charge rate via ac current on the converter and battery voltage. I have a PD so I can keep it at any of the three charging voltages I want with the remote.

With 2 banks I can disconnect 1 for a few hours or overnight to get a resting voltage. They are the GPL-6CT as someone else indicated.

A cheap RC $16 ebay amp Watt meter/volt meter, also counts the total number of amps that have been recharged. It gives you a cumulative total, every single time. You want to know that when recharging touchy lithium ion batteries.

[MEXICOWANDERER]

A lot of good answers above IMHO.

Having solar voltaic panels in my opinion belongs in a wholly different category because different charger methodology has absolutely nothing whatsoever to do with correct battery management AWARENESS.

By utilizing an amp hour meter, total amp hour transactions can be monitored and analyzed by the simplest of methods "Stare & Compare". A voltmeter especially with an AGM battery cannot do this.

An anology - Keep an accurate record of a checking account, versus advice to simply deposit a few extra dollars and forget about account reconciliation.

One of the gifts of an ampere hour meter is to notice and react to "Trends % Tendencies". T&T is generated and permutated automatically by your brain as you watch the ampere hour meter in operation. "I subtract X number of ampere hours, then allow X number of ampere hours to charge the batteries. What happens if I start the generator with otherwise fully charged batteries, apply (a voltage number, let's call it 14.4) and run the generator for a half hour. How many ampere hours will the bank gain?" The answer should be "How many amp hours SHOULD the bank gain" The answer, is "close to 0". Devise your own simple cross-check schemes. Just do not permit yourself to be mesmerized by a simple voltmeter - ammeter meter arrangement.

But don't fall for the "I don't want to be surprised and run out of gas question be answered with a "buy gas more often or get a bigger tank" off-the-wall analysis. The correct answer is "Install a gas gauge".

Ampere hours meters are easy to use, and fun. You'll learn a lot and the batteries will not take the brunt of guesswork operation and maintenance.

[Ductape]

NinerBikes wrote:

smkettner wrote:
I would get solar before the monitor.

I would agree with this. And if you get a little RC charger monitor with an amp meter hooked up in line while charging, with a little practice, your solar panels output capacity versus the voltage and amps the batteries are taking in will give you a really good handle on the State of Charge of your batteries.

If your solar panels are capable of 25 Amps, and your batteries are taking 14.3 -14.4V but only accepting 5 amps or less, you are pretty much topped off on charge on your batteries. The scenario changes a bit as fall and winter approach and the days get shorter, generator time might need to make up a bit early in the day when the batteries state of charge is lowest, then let the solar panel do the top off charging the rest of the sunny day.

This kind of what I was thinking. I can sort of read SOC crudely now by watching charge rate via ac current on the converter and battery voltage. I have a PD so I can keep it at any of the three charging voltages I want with the remote.

With 2 banks I can disconnect 1 for a few hours or overnight to get a resting voltage. They are the GPL-6CT as someone else indicated.

[jrnymn7]

Amp hour counting is much more reliable, overall, but volt meters have their uses. For instance, they make great charging monitors, for keeping an eye on whatever source you're using; be it solar, alternator, converter, charger.

The problem I have with using a volt meter for establishing SOC, is you cannot possibly get a proper read while the batts are either under load or being charged... which is probably 100% of the time, either way. And a single decimal place volt meter can be very deceiving. If for example it rounds up, like both the trimetric's and the xantrex inverter's do, a 12.4v reading could actually mean the batts are at 12.32v. On 300Ah bank, like yours, that's a difference of about 22Ah's. This may or may not be a concern for you.

And if you plan to boondock a lot, then you may want to consider using a charger, not a converter with a charging feature, if your new converter drops to 13.6v during absorption mode. This will reduce generator run times to less than half the time on a 300Ah bank. And yes, an inverter charger would be better as well.

And keep in mind, with two banks, that means two separate monitoring systems, which could get rather costly.

[msiminoff]

Ductape wrote:
Question I have is an AH monitor e.g. Trimetric seriously useful, or is a voltage check just as accurate (more accurate?) an indicator of SOC?

Hi Ductape,
Since you plan to boondock and have AGMs (can't check SG), IMO a battery monitor is a must-have item! Simply knowing voltage is not sufficient.

If it were me, I'd tackle the solar and battery monitor installations at the same time.

Keep in mind that the TriMetric only displays voltage to one decimal place. If you are content with knowing the SOC% with only 0.1V accuracy on voltage then it will serve your purposes just fine. I love having my TriMetric, but I also installed a small panel-mount volt meter so I can have better resolution for the voltage.

You will also get significant benefit (in terms of charge time and performance/service-life) by upgrading to an inverter/charger with programmable charge parameters and temperature compensation.

Cheers,
-Mark

[SteveAE]

Hi,

I think a battery monitor is a very valuable tool.

I would choose to get a battery monitor before solar and use it to determine daily usage so as to better size a solar system.

Have fun with your system.

Steve

[2oldman]

pianotuna wrote:
600 amp-hours is a nice bank. What jar size the the six volt batteries?

He said two banks, so I guess they're separate. I'm thinking if OP has 600ah in 4 6v he must have these.

90lb apiece.. ouch!

I use a voltmeter only. Works great.

[NinerBikes]

smkettner wrote:
I would get solar before the monitor.

I would agree with this. And if you get a little RC charger monitor with an amp meter hooked up in line while charging, with a little practice, your solar panels output capacity versus the voltage and amps the batteries are taking in will give you a really good handle on the State of Charge of your batteries.

If your solar panels are capable of 25 Amps, and your batteries are taking 14.3 -14.4V but only accepting 5 amps or less, you are pretty much topped off on charge on your batteries. The scenario changes a bit as fall and winter approach and the days get shorter, generator time might need to make up a bit early in the day when the batteries state of charge is lowest, then let the solar panel do the top off charging the rest of the sunny day.

[time2roll]

I would get solar before the monitor.

[pianotuna]

Hi,

You need an amp-hour counter with AGM batteries. I'd recommend the one from Victron rather than the Trimetric.

600 amp-hours is a nice bank. What jar size the the six volt batteries?

Are they wired in a balanced manner (this is possibly more important for AGM chemistries).

[Matt_Colie]

Duct,

This a battle I have been fighting for years without much success until I put in a Trimetric. If you are going to count on the house bank for much of your lifestyle at all, it is a very good investment. I don't care which one you choose, but a volt only is a waste of your time. A true monitor will tell you where you stand with little doubt.

As soon as I got ours on-line, I found out that the oven light was on. That saved a lot. Then I found out that our converter is too far from the house bank so I was not getting the charge rate I had been counting on.

Without such an instrument, you are blind about the actual battery state of charge and with AGMs, you can't even check the density.

I electric upgrades on performance cruisers (read retired racing sloops) for several years before the depression. This was always a recommended upgrade and always appreciated when the owner found out what he bought.

Matt