12vdc Panels, 24vdc Battery Bank

[Paul Elliott]

Originally Posted by cfarrar

As I understand it, if you connect your panels to the battery bus terminal posts, then there's no need to connect your battery monitor to the panels themselves. Your battery monitor should continue to operate as before. While the panels are providing charge, the battery monitor will display the resulting voltage and current flow into the batteries. That's what my monitor does.

Actually, with the panels connected directly to the battery terminals, the monitor will not display the panel charging output.

The battery monitor usually has a shunt resistor between the house ground point and the battery negative terminal, and this is how the battery current is measured. You should connect all loads and charging sources to the house ground, not to the battery negative terminal post. Some people argue that the SSB radio (if you have one) should connect directly to the batteries, but if this is done the radio may work better but the radio's current drain will not be monitored.

MPPT controllers do work, but if you have more money to spend you should first get all the panels you can afford (or can find a place for) and use a cheap controller. Then, if you still need more juice the MPPT controller may be a good upgrade.

[cfarrar]

You should connect all loads and charging sources to the house ground, not to the battery negative terminal post.

Sorry, poor word choice on my part. When I wrote "battery bus terminal post," I meant "battery bus power post." Ie, the DC positive post behind your electrical panel to which your battery cable(s) are attached, not the batteries themselves. The point is that you want the solar charger output charging all your batts even when the house battery selector switch is in the "off" position. As Paul writes, the charger's negative output goes to the house ground, which is probably the only large DC negative post in the panel.

To me the MMPT is a no brainer - it's no more expensive than the wattage equivalent of another solar panel, and it takes up zero space on top of my bimini.

[Paul Elliott]

Originally Posted by cfarrar

Your suggestion about maxing out your panels first, and using a cheap controller, makes perfect sense if you have plenty of real estate to put up panels, and you don't mind the weight and windage.

Exactly. Put up panels as many panels as you can stand, then go for the MPPT controller. Of course, you don't need to get the cheap controller if you think you will eventually want the MPPT.

By the way, I've had poor reliability from the Blue Sky MPPT controller. It seems that it only takes a few drips and the thing stops working. I've had two of them fail, with honestly only a tiny drip of salt water hitting it. I know I should have it better protected, but has anyone else had similar difficulties?

[Joe Simmons]

Originally Posted by witzgall

MPPT controllers also have the added benefit of using a pulse charging method that will top off your batteries a bit higher than conventional charging. This means more amps are available from your battery bank, and if they are wet cells, you will get longer life as they do not need equalization as much.

Chris

Cite please?

Batteries act as huge capacitors. Pulse charging seems useless.

[goboatingnow]

Pulse charging is not a standard feature of mppt controllers. Pulse width modulated charging of lead acid batteries is generally not recommended or supported by battery manufacturers. IUI or IUU charging regimes are.

[witzgall]

It is quite possible I got some bad info, or confused things myself. I retract my statement until such time as I can find some hard facts to back it up.

Chris

Originally Posted by goboatingnow

Pulse charging is not a standard feature of mppt controllers. Pulse width modulated charging of lead acid batteries is generally not recommended or supported by battery manufacturers. IUI or IUU charging regimes are.

[Paul Elliott]

I don't recall the source, but I did see a claim in a catalog somewhere that the (non-MPPT) duty-cycle style charge-controllers would reduce battery sulfation because of the high-current pulses.

I don't believe it though. While these controllers do generate pulses (they merely connect and disconnect the solar panel to control the average current sent to the battery), the current in the pulse is limited by the panel and isn't very high. And, even if the current pulses were higher, the efficacy of pulsed charging to reduce sulfation is questionable.

[nostramo.moody]

Hi guys, please help again,
I have now installed the panels in series and are currently giving about 3 amps at 24volt, however should one panel go into shade I get nothing at all,
absolutely zero although the other panel is in full sun.
Is there any way to avoid this as it is difficult on the boat to keep both permanently in full sun.
Cheers,
John.

[cfarrar]

John,

From what I understand, this is the disadvantage of wiring solar panels in series. If you had four panels - each paired to create 24V, and then the pairs wired in parallel to double your amperage - you would only suffer a 50% loss if one panel was shaded. If you want to stick with two panels, however, I don't know of any solutions, aside from mounting them to minimize shading. Hopefully someone else has a better idea for you.

[Paul Elliott]

There are MPPT controllers that will boost the output of the "12V" panels to match John's 24V battery. With one of these he could then wire the panels in parallel. One likely controller is from Genasun, the GVB series. I've not used these, merely looked at the specs.

As to whether it's worth spending a couple of hundred dollars on the controller, thats another question.