High Voltage I don't understand

Ronaldrwl

New Member
Joined
Oct 19, 2021
Messages
29
Location
Missouri
I have a 24v setup (27-28 usually) that can jump to 50v. The highest values I've ever seen are 21 amps and under 600 watts. I've measured the V output from the combiner box to verify what the charge controller is showing. Is something not working in the combiner box? Any help is appreciated. It may not mean anything, but this only seems to happen at 12-3pm and when the batteries are fully charged.

Details:
Monocrystalline Panels 10x195w 12v, 2s4p. 4 pairs of 2.
Combiner box, 60A max, 250V max in/out, surge protector, earth ground.
Charge controller 60A 12V/24V PWM
Inverter 3500/7000W 24Vdc-110Vac.
Batteries 10x50 amp LiFePo4 12v, setup as 24V
150amp fuse between batteries and inverter.
 

sunshine

Solar Addict
Joined
Apr 24, 2020
Messages
749
I've measured the V output from the combiner box to verify what the charge controller is showing. Is something not working in the combiner box?
Where are you measuring the 50v? A combiner box has no active components. That is the work of the charge controller. Is the inverter tripping out from over voltage?
this only seems to happen at 12-3pm and when the batteries are fully charged.
The V on the solar panel side of the controller will rise to Voc when there is no load. This occurs when the battery is full and other loads are small and not when "The highest values I've ever seen are 21 amps and under 600 watts." This needs to be clarified - are you getting the high reading at 600w?

What model is the PWM cc and what is the Voc of the panels(from a label usually at the back)?

The over voltage problem i had with my PWMs were fixed with a relay isolating a number of panels, combined with supercaps, whenever minimal loads and maxPV coincided.

Edit: reply with the panel Voc figure. A simple fix, and more appropriate for the 24v pwm, may be just 10p.
 
Last edited:

Ronaldrwl

New Member
Joined
Oct 19, 2021
Messages
29
Location
Missouri
I'm measuring the V at the output side of the combiner box, right before the CC. The voltage is also shown on the CC,
There is a load on the system. ps It's been working well for 6 months.
The high of 600w comes from 28V x 21 amps. These number are read from the CC screen.

Charge Controller from ECO-WORTHY
Battery voltage: 12V/24V
Battey Type: AGM,SLA,GEL,Li
Max Charge current: 60A
Discharge current: 60A
Max Solar input Voltage: <55V
Max Battery Voltage: <34V
Over-discharge return voltage: 12.5V/25V(Adjustable)

Combiner Box:
ECO-WORTHY 6 String PV Combiner Box is suitable for photovoltaic grid-connected and off-grid power generation systems. 6 String Configuration, Max current of single PV input array is 10A. Each String Continuous Duty Rated at DC 250V. Single PV input array installs with high voltage fuse, its...
www.eco-worthy.com
6 String PV Combiner Box
Number of Max Connection PV Array: 6
Max Input Current of Single PV Array: 10A
Total Input Current of PV Array: 60A
Max Input Voltage of Single PV Array: 250V
Max Output Voltage: 250V
Protection Grade: IP65
Operational Environment Temperature: -30℃~+70℃
Surge Lightning Protection: Yes

Solar Panel
Rated Power: 195W
Open Circuit Voltage (Voc): 21.6V
Short Circuit Current (Isc): 10.83A
Working Current (Iop): 9.02A
Output Tolerance: ±3%
Temperature Range: -40℃ to +80℃
 

sunshine

Solar Addict
Joined
Apr 24, 2020
Messages
749
Open Circuit Voltage (Voc): 21.6V
so called 12v panels.... I was wrong about the 10P ....keep the setup you have.

Max Voc of 2s is 42.2v....the CC is rated for <55v.....this is the problem as per other recent similar posts!
 

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
3,392
Location
USA
I know next to nothing about PWM charge controllers but I thought the idea was that you needed solar panels setup with a similar voltage to the battery voltage. You have a 24V battery but your panels in 2S will be over 40V.

An MPPT SCC will definitely work. Though the 150/45 is undersized for your panels. You have 8 (not 10) 195W panels in 2S4P. That's 1560W of panels. At 24V you need a controller that can handle 65A of charge current. The 150/45 only supports 45A. You should only use about 1200W of panels with the 150/45. If you do use the 150/45 you should consider 4S2P or 3S2P instead of 2S4P. You could actually do 6S as long as you don't ever get below -17ºF.
 

sunshine

Solar Addict
Joined
Apr 24, 2020
Messages
749
'm measuring the V at the output side of the combiner box, right before the CC. The voltage is also shown on the CC,
If your concern is only the 50V reading and no other problems it seems your system is ok.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
10,972
50 Voc - what are panel Voc, Vmp specs? I would think a bit of power is lost due to PWM pulling it down to 28V; likely MPPT would harvest more power. Probably sufficient Vmp on a hot day for minimum MPPT operating voltage, but check the specs and math (temperature coefficient of panels.)

PWM and LiFePO4? Keeping one leg in each century?
Does anybody think that is a good idea? It certainly couldn't hold battery voltage where balancing could take place.
All the more reason to select an MPPT SCC.

150A fuse seems to low for 3500W inverter at 24V. It's right on the edge before considering inefficiency (90%?), ripple current from battery (112%), margin to avoid nuisance trips (125%).
I'd like to have 225A. (slow-blow of class T would allow 7000W surge)
 
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