Battery SOC meters and Specific Gravity Don't agree, which to believe?

Jbergevu

I have an off grid system on a vacation cottage in Canada. For some reason my Tristar is showing the yellow+red LED (at night) which means 0-30% SOC. During the day the TriStar will show a Green LED just about as soon as the sun hits the modules. I know the batteries aren't getting charged that quickly. I was alarmed to see the SOC that low on the TriStar so I tested the Specific Gravity. I had just equalized the batteries earlier today as this was the first full day i was at the cabin. When I tested the SG tonight it was at 1.265 on all batteries. This clearly indicates the batteries are charged.

Also, I have a ME-ARC Remote Control on the Magnum inverter as well as a BMK (Battery Monitoring Kit) installed in my Magnum Mini-Panel. When I checked the SOC on the Magnum it also showed 99% SOC.

My question is, why would the TriStar show Yellow+Red LED when the Specific Gravity clearly shows the batteries to be charged? Also, if the TriStar doesn't accurately know the SOC how can it accuratly charge the batteries?

Thanks for any help you can provide.


System Description:
8 (235w) Yingli Modules
3 modules in series
3 panels in parallel
1 Magnum Mini Panel
1 Magnum inverter
1 Tristart 60 MPPT
8 Rolls 6v batteries in parallel (48v system)
1 TriStar Voltage sensor
1 TriStar Temp sensor

Vic

Re: Battery SOC meters and Specific Gravity Don't agree, which to believe?

Hi jbergevu,

Welcome to the Forum.

OK, Thank you very much for starting with a Signature, describing your system.
There are a couple of typos in that Signature. So you have nine PVs, arranged in three strings of three. And, the Rolls batteries are a single string of eight batteries is SERIES.

If the Tristar CC was showing the low battery LED status prior to your EQ, perhaps it will be different tonight (?).

Normally, Charge Controllers show battery State Of Charge based on voltage only.

SG readings are the Gold-Standard of true SG. Sometimes, if the electrolyte level in the batteries is low, the SG can read a bit high. You might check the levels and add Distilled Water as needed.

Also, sometimes, Hydrometers CAN give false readings, particularly false high readings, if the Hydrometer is not rinsed two, or three times with distilled water after each measuring session. Failure to rinse it well will allow sticky residue to build up on the inside of the Hydro. This allows air bubbles to stick to the outer tube and, especially the float. This can cause the float to be more buoyant, allowing false high readings (often high, but not always).

More later. Have Fun, Vic

vtmaps

Re: Battery SOC meters and Specific Gravity Don't agree, which to believe?

Jbergevu wrote: »

For some reason my Tristar is showing the yellow+red LED (at night) which means 0-30% SOC. During the day the TriStar will show a Green LED just about as soon as the sun hits the modules. I know the batteries aren't getting charged that quickly. I was alarmed to see the SOC that low on the TriStar so I tested the Specific Gravity. I had just equalized the batteries earlier today as this was the first full day i was at the cabin. When I tested the SG tonight it was at 1.265 on all batteries. This clearly indicates the batteries are charged.

Also, I have a ME-ARC Remote Control on the Magnum inverter as well as a BMK (Battery Monitoring Kit) installed in my Magnum Mini-Panel. When I checked the SOC on the Magnum it also showed 99% SOC.

Welcome to the forum,

I think the tristar lights are based on voltage. Voltage is not a reliable way to judge SOC... unless the battery is disconnected from all chargers and loads for a few hours. And even then, it's not a great way to judge SOC. Trust your hydrometer.

Battery monitors that use current shunts can count amphours in and out of the battery, and with enough programming can be quite useful, but they can only estimate the SOC based on many assumptions (temperature, peukert factor, age and condition of battery). If the battery monitor disagrees with the hydrometer, trust the hydrometer.

Jbergevu wrote: »

if the TriStar doesn't accurately know the SOC how can it accurately charge the batteries?

Charging the batteries is based on the absorb voltage and amount of time at that voltage. You must choose the voltage. There are a number of ways for a controller to end the time in absorb. Most use a fixed time. Some measure the current and when it declines to a certain point (end amps) the controller ends absorb.

Your goal is to find out what is the minimum voltage and the minimum time that will achieve a full charge (as confirmed by hydrometer). Voltage and time that are higher and longer than necessary will shorten the life of the battery, but far and away the greatest threat to your battery is sulfation caused by inadequate voltage and time.

You are fortunate that you have flooded batteries and can use an hydrometer to really know what is going on.

--vtMaps

Plowman

Re: Battery SOC meters and Specific Gravity Don't agree, which to believe?

I don't pay any attention to my Tristar LED, I find it useless. Doesn't seem to reliably correspond either to my meter or to battery SOC as measured with hydrometer.

I look at my meter to see voltage and amps to guestimate what stage the charge controller is in (can be hard if there's a significant load). I check batteries' specific gravity if I want to know SOC. Hydrometer always gets last say.

Jbergevu

Re: Battery SOC meters and Specific Gravity Don't agree, which to believe?

Thanks everyone for the replies. This helps a lot. I didn't know how important it was to clean the hydrometer so I'll be sure to do this going forward.