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Jammer · 01-06-2012, 10:16 AM

Does anyone have any experience with the Xantrex LinkLITE/LinkPRO battery monitor, the Trimetric TM-2025, or the Clipper BM-1?

dznf0g · 01-06-2012, 10:25 AM

I have the TriMetric...like it a lot.

Edit: TriMetric TM-2025RV, there are 3 variants

lewster · 01-06-2012, 10:37 AM

Take a look at the Magnum ME-BMK battery monitor. Excellent unit!

Jammer · 01-06-2012, 11:04 AM

Lewster, my understanding was that that unit can only be used in conjunction with Magnum's charger-inverters. Is it in fact stand-alone?

bryanl · 01-06-2012, 11:43 AM

I like that "integrating ammeter" label. It describes what they try to do and is much more appropriate than "battery monitor."

The OP asked for 'experience' - well, yeah, the integrating ammeters are indeed fun to watch and most of them do have battery monitors (i.e. they usually measure volts, too). As for telling you things about your battery, that is another question.

Probably the best idea I have seen for an in-use battery monitor is that at smartgauge.com.com but those don't seem to be available outside of the U.K.

For me, the first question is what, really, is the question? Are you looking for something that tells you net energy flow into and out of the battery? Or for something that will tell you state of charge? Or for some estimation of energy capacity left in the battery?

I do note that many integrating ammeters are improving. The early ones were single variable over time. Newer ones have rudimentary Peukert consideration. I haven't seen any that really deal with temperature effects in the net energy use integration, though (that is mainly used in float voltage considerations). Those factors are why predicting remaining available energy capacity is 'iffy' (you have to predict those as well).

If you are looking for current state of charge of your batteries, a DVM properly used and interpreted will provide as good or better a result as any other method. Hydrometry should be avoided due to hazmat needs. Integrating ammeters tend to be rather expensive and need a lot of care to make sure you know what it is you are measuring.

Jammer · 01-06-2012, 12:07 PM

Many goals for these things:
1) To get a reasonably accurate indication of the state of charge without having to disconnect loads or charging sources (as would be necessary with a DVM)
2) To get a window into the amount of energy the batteries are actually able to store so as to better plan replacement. Should also help with early identification of any battery string problems like loose connections.
3) To better understand what's going on with charging systems, particularly the charge line to the tow vehicle, but to a lesser extent what the converter is actually doing
4) To get a window into the actual energy usage over time for things like the furnace so as to develop better strategies for power management and a better idea how many watts of solar we would need to get one more day, how much difference a Dickson heater would make in battery life (by not using the furnace) etc.

I know they're not perfect but it doesn't seem like they're much more trouble or expense than an ammeter and shunt and they provide considerably more information.

dznf0g · 01-06-2012, 12:09 PM

The Tri-Metric will tell you just about anything you want. Some understanding of electricity and batteries is required if you choose level 2 or 3 of it's capabilities. It includes DATA for extensive diagnostics of batteries. If you go to Bogart Electronics' website, I believe the owner manual is there. It is NOT a casual user self explanatory interface with anything above level 1 programming.

bryanl · 01-07-2012, 08:49 AM

good goals!

batteries won't cooperate with you on most of them very much, though.

The issue is plagued by perception problems and a poor understanding of the variables involved. That means a lot of confidence in results that isn't warranted and may lead to disappointment. (it also leads to a lot of contention in these discussions as variables and context can lead to divergent experiences and mental models)

All measures of state of charge require a 'quiet' battery and proper interpretation in regards to context and equipment. There are only two direct measures of state of charge: voltage and specific gravity. For most RV purposes, a voltage measure after a half hour or so of no significant charging or discharging will provide close enough measure of state of charge.

The available energy capacity of a battery can vary by more than 10% due to factors such as temperature, cycle to cycle variations, age, and use profile. The problem with most integrating ammeters is that you have to program them with the bank capacity, which is not known very well, and then their integration of power doesn't consider all of the important factors. They provide a lot of reassuring precision but their accuracy is another thing.

For charging systems, the ammeter is nice but, again, all you have to do is to watch how the battery voltage responds to its inputs. One factor many seem to miss is that a lead acid battery needs 8 to 12 hours or more for a complete and full charge even with the best equipment.

Getting a window on actual energy use is plagued by both the inherent variabilities in lifestyle and the constraints of a battery system. Figure a typical household uses 30 kWh/day (government numbers) while the typical Airstream battery bank has a bit over 1 kWh available energy which should last a weekend. Yeah, an RV is not a house, but, still, a 30:1 ratio to start is a big jump and it means that just a few degrees on your thermostat on a cold night can make the difference between whether or not you have any battery left in the morning.

You just don't have the room or carrying capacity in your Airstream for more than a few hundred pounds of battery or more than a few hundred watts of solar so something's got to give. There's also the cycle depth issue as a reserve to consider.

Some rules of thumb to think about: - Lead acid batteries have about 12 to 15 watt hours per pound of usable energy. - A solar system should be sized for at least a watt for each pound of battery. - Batteries need 4 watts per pound maximum charging capabilities for best health.

Quote:

it doesn't seem like they're much more trouble or expense than an ammeter and shunt and they provide considerably more information.

hey, they are fun! If they don't cost much and aren't much trouble to install and you like numbers, then go for it! You do get a decent DVM and a good ammeter and those can be useful. Just be careful about the idea that having more information is going to help you achieve your goals. Sometimes it can mislead or distract if you aren't careful.