Hi Steve
You've packaged up few different questions there and lets start whether to charge the propulsion bank or house bank...
Its useful to stay with watts when comparing charging at different voltages. Amps is not such a good measure because it gives a misleading sense that you'd be getting more power if you charged the house bank. You've done the numbers right and it is the same amount of watts however you adapt it for high or low voltage.
And you are right that lots of power will be wasted if you directly charge the house bank. Your propulsion bank could be down and your solar panels producing plenty of power but with nowhere to go once the house bank is full.
I think it does make sense to charge the propulsion bank cos this is where you have the capacity to utilise the power that you' d be producing.
MPPT controllers are already adjusting the voltage to match the battery voltage anyway so it does't matter much that they'd be adjusting the voltage higher or lower to suit whichever bank you choose.
Regarding load dumping, for now I suggest its best to abandon that possibility because there aren't any controllers that we've heard of that do both. So you might as well go for MPPT because you'll be needing to change the voltage anyway. And with a large propulsion bank that can probably take all the power that you can throw at it most of the time, you'd probably not often see excess anyway. (I'm assuming you'll choose to charge the propulsion bank). If you do find that you can easily keep the batteries charged and often have excess, then you could add a diversion controller later when its clear that it would have some work to do.
You'll need to find a supplier who can provide a controller that will convert from whatever voltage your panels are, to the 144v of the propulsion bank. (or actually some higher value which is your proper voltage to charge that pack). Solar Converters Inc in canada produce a variety of charge controllers that will adjust the voltage to suit your requirements. I suggest it would be good to have a controller for each panel, thus maximising your output in the case of one of the panels being shaded, which can often happen on sailing boat.
I hope that helps
Cheers
Chris
On 27/06/2012, at 10:53 PM, Steve Dolan wrote:
I've just started to learn and consider solar panels for Electra Glide and could use some input from you guys. I would like to go with 2 panels, probably the Sun 210's giving me 420W total off my dingy davits.
The current system:
I have 144V pack of 12 AGM's but plan on a LiPo4 pack in the future as my propulsion bank. I also have 3 AGM's for my house bank at 12V. The Propulsion bank charges the House bank through a charger/converter (144V to 12V). The shore, regeneration, and genset charge the propulsion bank.
Ideally I would love to charge the Propulsion Bank but if my math is correct I'll only get about 3A at 144V to the bank from solar. The same 2 panels will give me about 35A at 12V if I connect to the House Bank.
Most of the loads during sailing come from the house bank but I don't think I'm using 35A worth of electricity at any time so a lot would be wasted.
Questions:
Does it even make sense to consider going to the Propulsion Bank?
Most solar panels I've seen in the higher Wattage are 24V or higher, does the MPPT convert this to 12V output?
If the MPPT does load diversion (diverting power to a device such as a water heater or frig (Load Dumping?)) is this normally a connection at the MPPT of the device or does the device know not to get power from the house bank at the same time? This part is really confusing to me, I guess with a HWH you can control the device power input with a thermal switch but if I wanted to run a frig it has no such shut-off switch. For that matter what happens when you don't have sun for a few days and the wife just used up the 11gal tank?
Like I said I'm just know getting into this and think that the solar panels are the way to go it's just confusing on some issues.
Thanks in advance,
Steve in Solomons MD
Lagoon 410 SE
