Excessive voltage measured on my 12V panel (about 40V open circuit)

[Gueyome]

Hello , I am unable to use my solar panel (HQST, 100W , 12V panel) my battery (ExpertPower) is designed able to take 12-18V input from a solar panel, but when I measure the voltage of the panel under direct sun with a multimeter, I get 40V ... what can be the problem? unfortunately the battery would not charge with this panel

[sdold]

Hi Gueyome, welcome to the forum. That panel should give you around 21V open-circuit (nothing connected, just measuring the terminals). If you see 40V, I'd suspect your voltmeter has a problem, or you're measuring two panels in series.

A charge controller is required between the panel and battery, are you using one? What's the model number of the battery?

[Tecnodave]

Gueyome,

How many cells are on that "12 volt" panel? It should be 36 cells at .5 volts per cell for a monocrystalline or polycrystalline cell panel. If there is some other cell count it's not a true "12 volt " panel. That voltage would be for an 80 cell or 72 cell panel maybe? It could be used with a MPPT type of controller.

[Gueyome]

It is a standard panel bought on Amazon, I don't have it with me currently, but I'm pretty sure it's this one (32 cells) 12V https://www.amazon.ca/HQST-Monocryst...gateway&sr=8-3

The battery is a battery pack made by Expert Power, model Omega288. It has a solar charge feature, so I figure it doesn't require an additional charge controller. It is rated 18V 100 W max input, according to the manual. https://cdn.shopify.com/s/files/1/23..._Omega_288.pdf.

The next test I could try to run would be to try to charge the battery with another panel (from a friend). As soon as I find out I'll post if the problem comes from the battery.

[Gueyome]

I thought I posted an answer with the models of the panel and the battery, but I don't see the post. Solar Panel HQST 100W 12V (32 cells) https://www.amazon.ca/HQST-Monocryst...sr=1-3-catcorr and the battery is ExpertPower Omega288 (has a solar charge feature, so I assume I don't need a charge controller) https://cdn.shopify.com/s/files/1/23..._Omega_288.pdf

[sdold]

The post was OK, it just had some links that sent it to moderation. The 18V maximum input to the Omega 288 is kind of strange; a typical "12V" panel has 36 cells and an open-circuit (unconnected) voltage of around 21V and a "max power" voltage (Vmp) of 18V. It would be strange if they had designed this unit with something else in mind. Maybe it was necessary since the battery isn't your typical lead-acid type. If you don't get a definitive answer it would be worth talking to manufacturer about the recommended panel type.

[Gueyome]

I did some new tests today to make sure my multimeter was not failing last time. Now when I measure the voltage out of my HQST 100W solar panel (12V) under bright sun, open voltage goes up to 29.8V . Is it normal (for a 32-cells panel?) . I attached a small picture to give you an idea of the panel's size and shape.

[PNPmacnab]

Just as a check, why don't you measure something known like your car battery. And is that battery icon displayed on the meter. Lots of strange readings when you meter battery is low.

[sdold]

Now when I measure the voltage out of my HQST 100W solar panel (12V) under bright sun, open voltage goes up to 29.8V . Is it normal (for a 32-cells panel?)

No, it's not. The suggestion to measure your car battery is good because it sounds like your meter is reading high. I think that panel should be 21-22 volts open-circuit based on the Amazon ad:

Product description

The HQ 100 Watt 12 Volt Monocrystalline Bendable Solar Panel uses advanced SunPower monocrystalline cells that have been laminated into a thin plastic sheet. The result is a solar panel that is far more durable and efficient than traditional glass and aluminum models. Weighing in at a mere 4 pounds, this panel is great for stealth and effortless to transport, hang, remove, or use for non-permanent applications. Also, unlike traditional panels, while this panel may be damaged by sharp objects or scraping, there is no risk of shattering or cracking.

Specifications:
Maximum Power: 100W
Maximum System Voltage: 600V DC (UL)
Optimum Operating Voltage (Vmp): 17.7V
Optimum Operating Current (Imp): 5.70A
Open-Circuit Voltage (Voc): 21.7V
Short-Circuit Current (Isc): 6.10A
Dimensions: 41.7 X 21.3 X 0.12 inches
Weight: 4lbs

Please note:
These are flexible panels, not bendable panels. Be very cautious when removing panel from packaging and when transporting. Make sure to not bend the panel.