Is my PV fully charging the batteries?

[goeasy123]

I have two 230W arrays going through two networked Victron 100/20 MPPT chargers. On day one after a night of sailing and depleting the 420Ah of batteries the MPPT chargers each generated around 980Wh, 61% bulk, 8% absorb and 30% float. The max V was 14.15V, min 11.99V. At the end of this first sunny day the Mastervolt monitor said the batteries were at 100%.

Progressively and by day 4 the MPPT chargers generated 450Wh, 38% bulk, 8%, absorb and 54% float. Max V 14.15V, min 12.35V. Same sort of sunny days. But the Mastervolt monitor said the batteries were only at 85% when the chargers go into float.

Are the batteries being fully charged and is the Mastervolt monitor losing its reference?

 

[noelex]

The best reference is to note the "battery return amps".

This is the current entering the battery at the absorption voltage. When "fully charged" the figure should be between 0.5%-4% depending on the battery specifications. In practice the percentage will drop rapidly as the battery approaches full charge so the exact percentage is not as critical as it sounds. If there are no specifications available for your particular battery type, 1% is a reasonable number.

As an example, my battery bank is 600Ahr and my absorption voltage is 14.4v so when the batteries are accepting 6A or less at 14.4v they are "fully charged" and a drop to float is appropriate.

If the battery monitor is not reading 100% charged when these criteria are met, it needs to be reset.

If the solar charge controller is dropping to float before these critera are met, the absorption time needs to be increased.

 

[goeasy123]

The best reference is to note the "battery return amps".

This is the current entering the battery at the absorption voltage. When "fully charged" the figure should be between 0.5%-4% depending on the battery specifications. In practice the percentage will drop rapidly as the battery approaches full charge so the exact percentage is not as critical as it sounds. If there are no specifications available for your particular battery type, 1% is a reasonable number.

As an example, my battery bank is 600Ahr and my absorption voltage is 14.4v so when the batteries are accepting 6A or less at 14.4v they are "fully charged" and a drop to float is appropriate.

So, is this right.... What it need to do is turn off and on the 2 MPPTs to force them into absorption. Then with my 420Ah batteries, if I see 4A or less the batteries are probably fully charged? ... but I should have no loads on.

 

[pvb]

14.15 max voltage is rather low.

 

[noelex]

So, is this right.... What it need to do is turn off and on the 2 MPPTs to force them into absorption. Then with my 420Ah batteries, if I see 4A or less the batteries are probably fully charged? ... but I should have no loads on.

If you have a battery monitor it will measure the current entering the batteries, so the load will not effect the reading, but if you are relying on MPPT output current you need to subtract the load current.

So, in your case with battery return amps at 4A or less at the absorption voltage, the MPPT should drop to float and the battery monitor should read 100% SOC.

Ideally there should be no need to turn the solar controllers off and on. They should remain in the absorption mode until the 4A criterion is met. If the solar is regularly dropping to float before this criterion is met, the absorption time needs to be increased.

 

[noelex]

14.15 max voltage is rather low.

14.15v is lower than most manufacturers suggest, although if they are gel batteries this may be correct.

It is best to check the correct absorption voltage with battery specifications from the manufacturer and then it should be adjusted for temperature. Ideally, you should measure this voltage at the battery. Small differences in this value make a significant difference. If there is a conflict in the manufacturer's recommendation, erring on the higher rather than the lower side and slightly overcharging the batteries is usually better.

 

[goeasy123]

So, in your case with battery return amps at 4A or less at the absorption voltage, the MPPT should drop to float and the battery monitor should read 100% SOC.

It never reads 100% when we're out on anchor. It decreases more each day, but the float current reaches less that 4A pretty early on a sunny day. After 4 days it's down to 90%. This makes me think the battery monitor is drifting??

BTW the absorption voltage is set to 14.4V in the Victron app. I'm not sure why the recorded voltage is only 14.15V?

 

[noelex]

It never reads 100% when we're out on anchor. It decreases more each day, but the float current reaches less that 4A pretty early on a sunny day. After 4 days it's down to 90%. This makes me think the battery monitor is drifting??

It is not the battery return current at float voltage that is important, but rather the current at the absortion voltage.

The current at float voltage will be lower so if the battery is accepting 4A at float voltage a SOC around 90% may be accurate.

 

[geem]

It never reads 100% when we're out on anchor. It decreases more each day, but the float current reaches less that 4A pretty early on a sunny day. After 4 days it's down to 90%. This makes me think the battery monitor is drifting??

BTW the absorption voltage is set to 14.4V in the Victron app. I'm not sure why the recorded voltage is only 14.15V?

Temperature compensation?

 

[goeasy123]

It is not the battery return current at float voltage that is important, but rather the current at the absortion voltage.

The current at float voltage will be lower so if the battery is accepting 4A at float voltage a SOC around 90% may be accurate.

I understand. I think I gave you duff info. I'm pretty sure the current at float voltage was showing much lower than 4A.

Forgive me for being dumb! I seem to have plenty of sun and PV capacity to charge the batteries up to 100% each day. I'm only running a small fridge and freezer and an LED anchor light. But every day the SOC is slightly lower than the day before. If the Mastervolt monitor is not drifting how do I get the batteries to full charge?

 

[noelex]

I understand. I think I gave you duff info. I'm pretty sure the current at float voltage was showing much lower than 4A.

Forgive me for being dumb! I seem to have plenty of sun and PV capacity to charge the batteries up to 100% each day. I'm only running a small fridge and freezer and an LED anchor light. But every day the SOC is slightly lower than the day before. If the Mastervolt monitor is not drifting how do I get the batteries to full charge?

If you have plenty of solar power and the batteries are not reaching 100% SOC according to the battery monitor, then either the battery monitor is reading incorrectly or the solar controller is dropping to float too soon.

These problems can usually be fixed by adjusting the settings on the battery monitor or the solar controller, but first you need to determine where the problem lies.

Monitoring the battery return amps is the best way determine this, By monitoring this value you know which device needs adjustment.

 

[goeasy123]

Thanks.

 

[stranded]

Thanks.

I have had a couple of questions along this line I. The last few days. In my case the problem has been diagnosed as the solar charge not being counted by my Mastershunt because I wired the solar regulator directly to the batteries. The Mastershunt derives it’s SOC from watts in/watts out - if it is not measuring the watts in as in my case the soc will inevitably drift down, especially as we leave high summer so the fall back benchmarks - variations on x volts above float voltage for y hours - are not triggered. I will in response to advice here be rewiring the solar regulator directly to the positive and negative terminals on the load side of the Mastershunt so the solar voltage is fully taken into account. Haven’t been down to do it yet but the advice was sufficiently authoritative that I have no doubt that will resolve the problem in my case. Yours may vary of course.

 

[goeasy123]

I have had a couple of questions along this line I. The last few days. In my case the problem has been diagnosed as the solar charge not being counted by my Mastershunt because I wired the solar regulator directly to the batteries. The Mastershunt derives it’s SOC from watts in/watts out - if it is not measuring the watts in as in my case the soc will inevitably drift down, especially as we leave high summer so the fall back benchmarks - variations on x volts above float voltage for y hours - are not triggered. I will in response to advice here be rewiring the solar regulator directly to the positive and negative terminals on the load side of the Mastershunt so the solar voltage is fully taken into account. Haven’t been down to do it yet but the advice was sufficiently authoritative that I have no doubt that will resolve the problem in my case. Yours may vary of course.

That one stung me too. I had the -ve of the output from the MPPTs in the wrong side of the shunt. I think I have an inherent problem with the Mastervolt monitor. I'm going to try a Smartguage monitor. SmartGauge Electronics - Homepage

 

[Gumpy]

That one stung me too. I had the -ve of the output from the MPPTs in the wrong side of the shunt. I think I have an inherent problem with the Mastervolt monitor. I'm going to try a Smartguage monitor. SmartGauge Electronics - Homepage

Smartgauge is great if you dont have solar. It is not accurate when charging ( about +/- 10% ) which you wiill be in daylight hours.
I have got into the habit of reading mine when I get up for my middle of the night abloutions