Need help please, Don't under stand what went wrong

Re: Need help please, Don't under stand what went wrong

Ah, the lovely, nutty contest of "current source vs. Voltage source"!

Oh, and let's not forget Voc vs. Vmp. It makes a big difference which one your measuring. The Open circuit Voltage (Voc) is often 8 Volts higher on a "12 Volt" panel. The Voltage at maximum power (Vmp) is usually around 17-18 for the same panel. What it is on homemade panels is anyone's guess.

Most probably your charge controller didn't like see 20+ Volts on its input, especially if that is at Vmp. If these were "standard" panels you'd be putting 35 Vmp through a PWM controller, and with a 12 Volt system most of that power is just wasted. Basically the Voltage is "dragged down" and the current never goes above that of one panel, regardless of the fact there's two in series. PWM controllers can not make use of higher Voltage to create Amperage. Re-arrange the same panels in parallel and all of a sudden you're pushing full Amps.

Here's a suggestion: measure the input Voltage on the charge controller when charging. Check it with each panel individually. It's not perfect, but it will give you some idea of the Vmp on the panels. Hopefully it will be around 17 Volts. If you've got one that's 2 Volts lower, it's a waste of time to hook that in with the others as it won't really be contributing anything to the charging.

Re: Need help please, Don't under stand what went wrong

If the Vmp rating per cell is 0.5 Volts and you put 36 of them in series the Vmp of the panel should be 18. If you put 40 of them in series the Vmp should be 20.

If you've got panels whose Voc is coming in around 12 Volts they'll be useless in charging a 12 Volt battery. If these were built with broken/defective cells chances are they can't put out their rated Amperage either.

If your other panels are coming up with a Vmp of only 12 Volts they're not going to be much good at charging the battery either. Normal Vmp for a "12 Volt" panel is 17-18; you have to have more than battery charge Voltage in order to push the battery Voltage up.

Let's say you have two typical "12 Volt panels": Vmp 17.5, Imp 7.5. 17.5 * 7.5 = 133 Watts (more or less). Put two of these in series and feed it through a PWM type controller to a 12 Volt system. The array Vmp is now 35 but the Imp remains 7.5. Trouble is, there's nothing to convert that "extra" Voltage to current. The panels Voltage is dragged down to charging level (around 14.4 Volts, more or less) and the extra power potential is just plain lost as panels are current sources not Voltage sources and the current can not exceed the maximum. You'll still only get about 7.5 Amps into the 12 Volt battery. If it were a 24 Volt battery you'd get 7.5 Amps, but at the higher charging Voltage. This is why the same PWM controller can be used with different system Voltages, but the array has to be at the right Voltage level for charging because there is no circuitry to adjust that here. Likewise if the panel Voltage is too low there's not enough to push the current (as in some panels with "odd" Vmp's like "23.4" trying to be used on a 24 Volt system that needs 28+ Volts to charge).

To extend that "odd" Vmp example: say it is a 210 Watt (available or nominal) panel and you have it on a 12 Volt system. Basically you lose the percentage difference between the panel Vmp and the system's "ideal" Vmp (over-simplification here; any engineers reading this are now cringing). About 25% of the panel's power potential, 52 Watts, is lost.

Normally a panel has cells in series to make a string, and then two or three strings in parallel to increase current. There's quite a lot of ways to do this of course, depending on what output is desired - in terms of Watts, Volts, and Amps. It sounds like yours are falling shy of what is needed to do a good job of charging. You have the "right number" of cells in series, but they don't seem to be living up to specifications. This can be caused by connection fault - or defective cells.

In case you're wondering, it's pretty easy to get the Voc out of a panel. I've seen broken ones put out 22+ Volts - until you put a load on. Then instead of 6 or 7 Amps of current they produce less than one.

Re: Need help please, Don't under stand what went wrong

Regrettably, Voc is not important. It can be high and yet the panel can be useless. It's almost impossible to get an accurate Vmp reading too. But you can get an accurate Isc reading.

Take each panel in turn. Set your multimeter on 10 Amps DC (it needs to be able to do this) and connect it across the leads of the panel. Place panel in full sun; read Amps. That number is more important than any other: it is the current ('I' - from the old term "Intensity") at short circuit. Panels are current sources, and they'll allow their Voltage to go all over the place while trying to put out their maximum current, which is dependent on the resistance of the load applied and the intensity of the light hitting them.

Try each panel separately on the controller. The "good" (18 Voc) panels should be able to light up the charge on their own, depending on the battery's SOC (that's the other variable that screws things up).

This is the whole trouble with testing panels: variables. Different light (and angle), unnoticed errors in connections, varying temperatures, changing loads, et cetera. It's no wonder you're perplexed/frustrated; what you're trying to work out is a difficult thing to determine. The tediousness of testing procedures doesn't help. Methodically checking each component under like circumstances is much easier in a lab than out in the real world.

My guess would be the two "10 Volt" panels are doing nothing and the "18 Volt" panels are providing the charge. Plus, that particular charge controller may be input limited to prevent over-Voltage conditions.

You can also skip the controller, for testing purposes, and just connect one panel at a time to the battery through an Ammeter and see what you get. You should be able to determine current flow (if the battery needs any) and see a slight rise in battery Voltage when the panel is attached.

It's bloody complicated stuff. Try to refrain from tearing your hair out.

Re: Need help please, Don't under stand what went wrong

I seriously doubt this is an MPPT charge controller - not for $30.

More likely "Boost Mode" is advertising hype for "Bulk Mode". "Boost" sounds more impressive than "bulk".

Re: Need help please, Don't under stand what went wrong

The Only Sarge wrote: »

Ahhh...I bet your right.;)

Did you look at that page the OP linked to? They repeatedly use the word "amplifier" where they mean "Ampere". That's the kind of quality tech-writing that instills confidence in you!