Solar Panel Charging Quirk

[Biggles]

Today I was charging with the Victron from the generator on fairly discharged batteries which before the sun got up were showing 11.43v. I only run the genney a few minutes to run the toaster and was getting 105amps charge.

 

Later on in the morning when the volt meter was showing 13.9v as the sun was out and the panels were dictating the voltage. When I started the genny again for a longer charge the new charge was 68amps

 

Now I know all these chargers work on a voltage, but clearly the batteries had not has sufficient charge form the solar in the time for the batteries to require this much less.

 

So I am now wondering if the solar should be switched out when a hard charge from the Victron is needed.

[magnetman]

I find at this time of year the solar input (400w 12v) on my roof does interfere quite severely with the normal generator regime (120a heart interface/mastervolt charger) which I have had on the go all winter. I find the batteries end up lower, the solar seems to confuse the charger. I have had the same thought about disconnectimg the solar during generator charging as the charger seems to see the high voltage and drop the amps.

 

the end of the day result being that the batteries have absorbed less charge

 

unless the batteries are shagged

[Justme]

I wondered about that too.

 

So I set up a test to see what would happen if each source was turned on / off in turn.

 

I was using a Victron 3000/12/120 & 1200watts of solar via a FM80 controller the battery bank at the time was 1550 ah @ 5c at about 60% SOC.

 

The result was that in each case the charge rate from each source was not affected by the addition of a second source.

 

I am guessing that in your cases the charge source to battery bank size ratio was a lot smaller than in mine so the rates dropped due to the bat not being able to accept any more current.

[Phil Ambrose]

I used to have 5 X 100 watt panels and charged by a variety of methods ie solar, engine , genny, shorepower all inputs to battery bank went through a Sterling Battery to Battery charger, sometimes a combination of these. I never had this issue oh and battery bank size was 990a/h

 

Phil

[Biggles]

I wondered about that too.

 

So I set up a test to see what would happen if each source was turned on / off in turn.

 

I was using a Victron 3000/12/120 & 1200watts of solar via a FM80 controller the battery bank at the time was 1550 ah @ 5c at about 60% SOC.

 

The result was that in each case the charge rate from each source was not affected by the addition of a second source.

 

I am guessing that in your cases the charge source to battery bank size ratio was a lot smaller than in mine so the rates dropped due to the bat not being able to accept any more current.

 

1180ah @ C20 and 490w Solar with MPPT Same Victron.

[Biggles]

I am going to try this again but with some covers for the solar panels.

 

I have the Tracker 40 MPPT maybe it would be easier to disconnect it but I'm not sure which side to disconnect the solar side of the battery side. I know there is a wrong one but can't remember.

[smileypete]

Today I was charging with the Victron from the generator on fairly discharged batteries which before the sun got up were showing 11.43v. I only run the genney a few minutes to run the toaster and was getting 105amps charge.

If that's a resting voltage then they're probably as flat as a pancake:

 

http://jgdarden.com/batteryfaq/carfaq4.htm#ocv_soc

 

Do you have a Smartgauge to look at? For traction batts I'd recharge ASAP when the resting or recovery voltage is below 12V.

 

cheers, Pete.

~smpt~

[leeco]

I always find that if i dont disconect the solar panels off the batteries when charging them with my engine I get funny readings on my volt meter.

[Biggles]

If that's a resting voltage then they're probably as flat as a pancake:

 

http://jgdarden.com/batteryfaq/carfaq4.htm#ocv_soc

 

Do you have a Smartgauge to look at? For traction batts I'd recharge ASAP when the resting or recovery voltage is below 12V.

 

cheers, Pete.

~smpt~

 

Nice tables.

 

My batteries were at 79% on the BMV600 gauge. It was only because I left the CH running for a week that the batts got that low.

[smileypete]

Nice tables.

 

My batteries were at 79% on the BMV600 gauge. It was only because I left the CH running for a week that the batts got that low.

The amp-hour counting batt gauges seem to have a well known and somewhat not entirely deserved reputation for telling outright lies.

 

So when the resting voltage is available it'd be good to use it from time to time to do a 'sanity check' on the batt gauge SoC reading.

 

cheers, Pete.

~smpt~

Edited April 7, 2013 by smileypete

[Biggles]

I have a hydrometer and use that as my definitive test on my battery condition. I do it about once a month but never seen a temperature reference table. From memory I think my hydrometeter is calibrated for 20c.

 

Best I have got on my hydrometer is 1255 but didn't know the temperature but it was much less than 20c.