Charge controller - two types of panels

BobJ
BobJ Registered Users Posts: 2
Greetings,

On my sailboat, I have a 42 watt flexible panel I use for maintenance charging and two Kyocera KC-40T's (43 watts each) that I bring aboard for long passages.

When aboard, the Kyocera's are run through a Flexcharge PV7-D dual-bank controller to two 92 Ah AGM's, and this has worked well. For a race this Summer I'd like to combine the three panels (add the flexible panel together with the two Kyocera's). I've also added a small AGM starting battery (21 Ah) that is isolated from the house bank by an automatic charging relay.

The amorphous panel puts out about 14 volts while the crystaline panels can put out 17 volts. Can I wire all three panels together through the PV7-D or will the different voltages be a problem?

If it's time for a new charge controller, what would you recommend for this setup?

Thanks.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Charge controller - two types of panels

    Your present charge controller is a "shunt" or "dump" type charge controller. You connect the solar panels directly to the battery bank, and the Charge Controller connects to a dump load (resistor bank to heat air/water). The controller "turns on" when the batteries are full.

    So, yes, you can simply put the present panels in parallel with the other panels in parallel.

    in general series controllers are considered to be "better" at charging batteries (they simply "turn off" the panel current when the batteries are full).

    With the extra panels, you may need a larger dump controller + shunt loads--Or just go ahead with a PWM (less expensive) or MPPT (more expensive, may not be needed for your boat) to charge your battery bank.

    If your amorphous panels are really only 14 volts (Voc/Vmp?)--That is really too low for the modern thinking about how to charge a battery bank (with a series controller). Ideally for a PWM controller on a 12 volt battery bank, you should be looking at Vmp~17.5 to 18.6 volts or so for various reasons.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge controller - two types of panels

    Welcome to the forum Bob.

    It's time for another charge controller. And possibly another panel.

    The Voltage on the two panel types are too far apart for them to work in concert. Basically the 14 Volt amorphous panel will be held above its Vmp by the crystaline panels meaning its current output will be little to nothing.

    As it is your two 43 Watt Kyocera's aren't much for a pair of 92 Amp hour batteries, or even one. They'd total about 5 Amps together, which is barely a 5% peak charge rate for 92 Amp hours, much less 184 (the two combined). I can only conclude that there is some other charging source for these batteries because the panel you've got would barely be a maintenance charge.

    That 14 Volt panel, btw, would barely be able to put any charge into a 12 Volt system. Between the panel being hot and the inevitable losses in wiring its Voltage output at the battery would not likely be more than typical resting Voltage.

    And if you're going to tell me that these panels have been doing all the charging I'm going to tell you the batteries are only surviving because of their capacity being higher than needed as that little panel power alone would clearly be a deficit charging situation.
  • BobJ
    BobJ Registered Users Posts: 2
    Re: Charge controller - two types of panels

    Thanks guys. Coot's explanation is what I suspected.

    Ours is an interesting exercise - a bit like the mockup scene in the movie "Apollo 13" (what can we run at the same time and maintain enough voltage for the autopilot, for example). We are careful to measure each load and then prepare a usage "budget" for the race.

    Yes, the primary charging is by the 35A engine alternator, but that is limited by fuel in a 2,100 nm race to Hawaii. I only carry 12 gallons due to fuel weight. In the 2006 solo race (SF to Kauai) I almost could have made it without running the engine at all, but we had too much cloud cover in the early part of the race. I used about five gallons of diesel in the 2008 solo race.

    I think I'll continue using the amorphous panel to keep the batteries topped off in the marina and put the two Kyocera's back aboard for the race. I thought the third panel would add something but it doesn't sound like it will.

    Are you guys allowed to recommend a particular controller (for the two Kyoceras)? The Flexcharge is 8-9 years old and I suspect there's a PWM type that would do a better job.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge controller - two types of panels

    For only about 10 Amps current you could use a Morningstar Sunsaver 10 http://www.solar-electric.com/ss-10.html but this doesn't have independent outputs for two separate batteries. If you really need the dual output you need a controller like the SunSave Dual http://www.solar-electric.com/modubachco25.html

    It would be nice if you could get some more panel on those batteries, but I expect you have space and weight limitations given the application.