Best battery monitor for State of Charge (SoC)?

[jeegro]

I'm planning out my setup, so far I've settled on the Blue Sea ML-ACR.

As far as battery monitors go, voltage is an okay measurement, but I like overkill and the ability to truly monitor the battery's capacity. The National Luna devices are basically glorified voltmeters.

Here are the options I've discovered, and all require the use of a shunt:

Blue Sea M2 1830 SoC Monitor
(cant post links)
This is the one I'm most excited about, it's new, but it's rather large, and you can only monitor the SoC on one battery.

Bogart Engineering
Ugly, large.

Xantrex LinkLITE
(cant post links)

Enerdrive
(cant post links)
Looks like the same as the xantrex unit, but rebranded


Are there any others I'm missing? It seems that none of them are capable of monitoring the State of charge of more than 1 battery/source. I guess that could be fine, since the starting battery is really only used for starting, so doesn't really need to be monitored.

My plan will also include a solar setup, shore charging port (thinking CTEK), inverter, fridge, etc.

 

[dwh]

SmartGauge

http://www.smartgauge.co.uk/

 

[dwh]

Also Victron. Pretty sure Victron has units that can handle more than one shunt.

I thought Bogart had a unit that could as well...PentaMetric maybe?

 

[jeegro]

Thanks. The Victron BMV-702 looks like a solid unit. Not as pretty as the Blue Sea though.

I'm thinking that I don't need to monitor more than 1 shunt. The starter battery just starts the car so should always be 99+%.

 

[LeishaShannon]

The BMV-702 does shunt/voltage for house bank and voltage for starter battery so it should be perfect for you.

 

[Joe917]

Whatever you get you want to be able to easily glance at the display to always know whats going on. So big display centrally located.

 

[jeegro]

I'm torn between the Victron and Blue Sea at the moment. I need to scope out some possible mounting locations and see what works best. In the meantime, I've switched focus on deciding what batteries to get.. limited space (max 2x Group 34's).

 

[loonwheeler]

I think one of the nice features of the Victron BMV-700 series is the ability to add a bluetooth smart dongle so you can use a connected device to monitor your batteries (if you are into that kind of thing). AFAIK Blue Sea does not provide this option.

 

[DaveInDenver]

As far as battery monitors go, voltage is an okay measurement, but I like overkill and the ability to truly monitor the battery's capacity. The National Luna devices are basically glorified voltmeters.

Here are the options I've discovered, and all require the use of a shunt

They are all just glorified VOMs, measuring voltage and current in & out to infer a state of charge from an initial trained (or possibly an entered value) baseline. Even then I wouldn't put that much faith into them without knowing the algorithm they are applying to judge SOC, which should at least know current battery temperature.

I know the SmartGauge has a sophisticated technique to judge SOC and the Xantrex Link boxes are well understood by boat owners. Another I know builds a faithful model is the Balmar (not on your list, here: Balmar Smartgauge ) units, their learning technique is sound but they do AFAIK a voltage-only technique, which is valid if done right.

Most fuel gauges are very simple and don't even adjust for rate of current usage (knowing rate is much better than just amp-hour counting at eliminating Peukert effect), charging efficiency or self discharge, which are critical to know true SOC. Your charger will do it's thing and you'll find over time your fuel gauge will no longer match the capacity of the battery as the actual SOH drifts from the measured and assumed. How much depends on the unit and how often you test your battery and recalibrate the gauge.

 

[DiploStrat]

A Thought

Your solar controller may already have a decent SOC display. The display on my Blue Sky ipnPRO is such that I would not have bothered to buy the TriMetric. (Other to watch the two of them argue over the SOC. )

Another thought, while it is interesting that you know the SOC, it is essential that your charging devices know it and respond - automatically. Don't fall into the "I need to know the SOC so that I will know when to charge." trap. With a lead acid battery, at least, the answer is: all the time.

Monitoring the SOC is useful to assure yourself that all is working as expected and, when really hammering the system, to let you know when you need to stop and take emergency action.

 

[jeegro]

Understood. Even though I am a techy-nerd (computer programmer), the bluetooth option doesn't really excite me. I can't think of a scenario where I'd be happy to disconnect my phone from the car stereo bluetooth, reconnect to the Victron, open the app, and get a reading on the batteries.

Are these monitors also compatible with LiFeMnPO4? I'm assuming yes, since as you guys have stated, they just measure current in/out, given an initial programmed aH.

 

[DaveInDenver]

Are these monitors also compatible with LiFeMnPO4? I'm assuming yes, since as you guys have stated, they just measure current in/out, given an initial programmed aH.

The ones here are for lead acid. The way SOH and SOC are determined is quite distinct between chemistries, so the answer is probably not with a hedged maybe.

Depends on the amount of error you're after. A simple voltage and amp-hour measurement can be adjusted to give a similar approximation for all chemistries but the overall error will be high (maybe +/- 10% or so) over any given period of time. The lifetime drift would be lower with LiFePO4 because they age slower.

 

[JaSAn]

I'll put my 2¢ in. Any of the amp counters (the ones with a shunt) will help you learn your system. I have a TriMetric 2030 in a prominent place in the camper and I looked at it a lot during my first year, but now much less. I know how much my refrigerator should be drawing, how many amps my solar is providing, . . . It alerted me to a couple of problems this year: my refrigerator door was not sealing well and on a rainy fall trip I had to continually monitor for falling wet leaves blocking the solar panels (I had to climb up and brush them off a couple of times a day).

jim

 

[DaveInDenver]

Another thought, while it is interesting that you know the SOC, it is essential that your charging devices know it and respond - automatically. Don't fall into the "I need to know the SOC so that I will know when to charge." trap. With a lead acid battery, at least, the answer is: all the time.

This statement has a ton of truth in it.

One of the places I recently worked had ongoing work with INL battery lab and a project they are involved with at Montana Tech dealing with online SOH calculations for large banks. They were primarily concerned with UPSes (the primary customer is cell tower owners) and to a lesser extent electric vehicle banks. They are doing electrochemical impedance spectrometry and intelligent charging and metering to eliminate the biennial standard replacement schedule the tower owners usually follow.

There hasn't traditionally been a fast and accurate method to judge battery health without taking the batteries off line and test them so they're developing reliable remote sensing to do that without waiting for failures or wasting good batteries as well as not requiring periodic site visits. They are able to build a bank model down to the cell level and these are not small installations, 10kW, -48V banks using on the order of 120 VRLA batteries (each the size of a 40mm ammo can) in a room-size rack.

Point here is that their research found that inaccurate SOC measurement leads to chronic undercharging, which meant battery condition was lower than the algorithm expected. That is you're putting an intelligent meter on the battery and then making bad decisions on what you believe is a trusted measurement that is, in fact, lying to you. Just making a calculated assumption and doing a so-called dumb 3- or 4-stage charge was actually better for the battery life than repeatedly adjusting the charge based on erroneous measurements. They had to adjust the routine based on the frequency and nature of discharges the battery experienced since the previous charge cycle.

 

[LeishaShannon]

Understood. Even though I am a techy-nerd (computer programmer), the bluetooth option doesn't really excite me. I can't think of a scenario where I'd be happy to disconnect my phone from the car stereo bluetooth, reconnect to the Victron, open the app, and get a reading on the batteries.

Its more for reading the historical stuff, seeing trends helps you understand whats happening over time, and when its time to replace the batteries. Same dongle can also be used in their MPPT controllers for the same reason.

Are these monitors also compatible with LiFeMnPO4? I'm assuming yes, since as you guys have stated, they just measure current in/out, given an initial programmed aH.

The Victron BMW works great with Lithium, you're able to modify the efficiency, perkert, tail current, etc etc to suit any battery type. Not sure about the others.