Solar panel question re OC voltage

Alberto

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Hi
My solar panel is not charging my battery, all appeared fine until a few days ago. (9 months charging lipo battery with no issues, 7 years charging FLA before this).
Victron mppt 75 15.
100w solar panel probably 8 years old.
Mppt says solar voltage is 12.94v 0A and unit is Off ( blue led flashing indicating no charge) multimeter agrees it's 12.94v
lipo battery is 80% charged so room for more.
Removed + wire from mppt PV pair and voltage reads 20.24v - reconnected and it drops to 12.94v
Checked panel OC voltage on roof at panel connectors and it is 20.24v, no corrosion on connectors.
Tried a new victron 75 15 and results are same

Looking at specs for new panel they claim OC voltage of 23/24 volts,

Have tried removing and reconnecting cables as per the install instructions
Does this mean my panel is faulty? I don't have access to a spare to try.

Regards
Al
 
From what you are posting your panel seems to be fine 20v is about right and as you get the same voltage at the controller it seems to rule out any problems from your panel to the controller. The solar voltage should not drop when you connect the battery. The solar output to the battery will be regulated by the solar controller. I think you may have an issue from the solar controller to the battery. There should be a fuse on the positive connection to the battery check it out. Also you may have low insulation within your battery or the cabling to the battery causing the solar voltage drop. If your battery has a BMS check it out for any issues. Also try disconnecting the battery to see if the solar voltage still drops. If it does not you may have a faulty battery.
 
Last edited:
Hi, thanks for replying.
Have tried 2 different solar controllers, both victron 75 15 mppt - same results
It's an old motorhome so control panel is basic
I Am able to boil kettle via inverter which was pulling 92A from battery, so am hoping the newish battery is still ok (fingers crossed).

Battery an solar panel are only things left in circuit, will measure short circuit current next. As usual for here it's started raining heavily so won't't go back on roof today.

Al
 
Alberto said:
Hi, thanks for replying.
Have tried 2 different solar controllers, both victron 75 15 mppt - same results
It's an old motorhome so control panel is basic
I Am able to boil kettle via inverter which was pulling 92A from battery, so am hoping the newish battery is still ok (fingers crossed).

Battery an solar panel are only things left in circuit, will measure short circuit current next. As usual for here it's started raining heavily so won't't go back on roof today.

Al
Click to expand...
Typical after boiling kettle the solar panel is pushing 1A into battery in the heavy rain.
Anyone want to buy a haunted motorhome 😀😀
 
Hi
Have not seen a setting to limit charge to 80%, I have seen battery charge at 100% a few weeks ago.
Boiling the kettle may have taken it down to 80% ish, sounds like a good explanation. ( Was getting close to 80% before I boiled kettle)
Thanks
Al
 
So, the open circuit panel voltage doesn't indicate a great deal TBF.
The voltage changes when hooked up to a battery (via the SCC), the new panel voltage will then depend on how much sun there is and what type of controller you're using. With an MPPT controller and decent sun the voltage typically fallss to 16-18 volts. As you're seeing 12.94v this is the actual battery voltage. This could be because you've got a PWM controller OR there's very little sun or the panel is knackered or there's a poor contact somewhere.
To be 100% sure you need to test the current flowing in the panel wiring and for that you really need a DC clamp meter, without one you'll be struggling and limited to diagnosing the issue by swapping out components.

I have a couple, the Uni-T ones are very nice but there are cheaper options, just make sure it measures DC current.
 
Hi
Thanks for your thoughts, the output rose at one point to over 3.5A when the sun peeked out. It's not a Flexi panel.
I'm now getting 0.4A at 6pm and overcast here in Lanarkshire.
Everything appears back to normal so I àm going with the 80% charge suggestion until it fails again 😭
Al
 
Very unlikely the BMS will stop allowing charge when the SOC hits 80%. Very undesirable behaviour and anyone who had a battery that did that should get it replaced!
 
merl said:
Something seems to amiss because 12.94 volts doesn't equate to a lifepo4 battery being 80% charged, rather somewhere nearer only 20% charged.
Are you getting the 80% battery capacity figure from the BMS or a shunt?
Click to expand...
Hi
80% is from the BMS,
Charging via solar panel started as normal this morning.
I have a Victron shunt, wonder if it would be worth installing it?

Would it be worth flattening the hab battery to zero everything and restart the charging? (only has 6 cycles clocked so maybe still learning? )

Thanks for all suggestions.
Al
 
Alberto said:
Hi
80% is from the BMS,
Charging via solar panel started as normal this morning.
I have a Victron shunt, wonder if it would be worth installing it?

Would it be worth flattening the hab battery to zero everything and restart the charging? (only has 6 cycles clocked so maybe still learning? )

Thanks for all suggestions.
Al
Click to expand...
I think I'm right in saying that how the BMSs establish remaining capacity varies between BMS manufacturers, some use Columb counting (like a shunt does) and some use voltage, some apparently use a mixture of both ?? Anyway whatever yours appears to be out of whack or possibly knackered so I think flattening or fully charging and resetting to zero or 100% would be a decent idea. As you appear to be closer to zero then discharging makes sense.
Because there's a question mark over the BMS reliability at the moment I'd definitely recommend monitoring the actual battery voltage with a multimeter while you do this and DON'T allow the voltage to drop below 10V.
Assuming you'll discharge with your inverter and a known load you'll then of course be able to establish pretty accurately what capacity you actually DID have left in the battery.
If you've already got a shunt then yes, get it installed, it's not a big job and will give you another layer of reliable info.
 
If I am ever unsure of my Lifepo4 SoC I will aways charge them until I know they are 100% full. I would get them on mains charger long enough to be sure then see what happens.

I have dumb lifepo4 though and the only SoC I use is my Victron shunt. I ignore everything but the shunt, has served me well for 6 years now.

Of course this won't help if you have a problem somewhere but you will know you started off fully charged then see what happens
 
Nabsim said:
If I am ever unsure of my Lifepo4 SoC I will aways charge them until I know they are 100% full. I would get them on mains charger long enough to be sure then see what happens.

I have dumb lifepo4 though and the only SoC I use is my Victron shunt. I ignore everything but the shunt, has served me well for 6 years now.

Of course this won't help if you have a problem somewhere but you will know you started off fully charged then see what happens
Click to expand...
Hi
Going to watch the solar charge the battery for a couple of days to ensure that the solar side is working and then I will charge via mains to 100% and monitor discharge via a small load.
Al
 
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