Anyone have experience with Renogy vs WindyNation PWM solar charge controllers?

[SunEagle]

We are to design a solar boat that will be used to race and tests its endurance. We are using an electric motor that we must find our selves. The specs of the motor are not restricted, however given a limited budget we will use what we have: a 12V minn kota motor with 55lb thrust. Two solar panels were provided for every competitor, 250W each. Battery we must find can be no more than 180 watts: 12V with 15Ah or 24V with 7.5Ah. We will have several rounds that include races and the distance the boat can travel in a given time (either time runs out first or the battery dies). Each round is either purely solar or purely battery. Having the solar panels connected to the battery during the rounds is forbidden. There were no requirements of charging the battery with the solar panels, that was strictly my own idea to charge in between rounds. I wanted to implement it just for learning purposes so I didn't know what to expect when I started this thread.

OK. So the event is to power a dc motor to power a boat using solar panels or a battery.

I will stick to my first statement that the people who thought up this event may not understand solar and batteries or expect you to design the system without telling you all that you need to know about basic electricity.

If the kota motor is only rated 12volt then using a 250watt panel that has a Vmp of more than 18volts can hurt that motor by exceeding it's voltage rating. So you will need to go with a 24volt motor and 24volt battery to truly compare solar panel power against battery power.

I can also tell you which power source will make the boat travel the furthest but maybe that is what you have been tasked to do so I will stop.

[Amy@altE]

Hmmm, then thinking out of the box here, what if you used a DC-DC converter like the Samlex SDC-60 to convert the high voltage of the panels in parallel down to the 12V motor? It would do the same as an MPPT, drop the voltage output and raise the current, but would be real time to the motor instead of charging the battery. I suppose you could have the battery on standby in case it's a rainy day during the race (always seems to work out that way).

[Wy_White_Wolf]

We are to design a solar boat that will be used to race and tests its endurance. We are using an electric motor that we must find our selves. The specs of the motor are not restricted, however given a limited budget we will use what we have: a 12V minn kota motor with 55lb thrust. Two solar panels were provided for every competitor, 250W each. Battery we must find can be no more than 180 watts: 12V with 15Ah or 24V with 7.5Ah. We will have several rounds that include races and the distance the boat can travel in a given time (either time runs out first or the battery dies). Each round is either purely solar or purely battery. Having the solar panels connected to the battery during the rounds is forbidden. There were no requirements of charging the battery with the solar panels, that was strictly my own idea to charge in between rounds. I wanted to implement it just for learning purposes so I didn't know what to expect when I started this thread.

Find a different motor and run it solar direct off the panels without a battery. A 24V trolling motor should beable to handle the voltage range of the panels in Parrallel. You would need to find one that's amp draw is below the combined IMP of the panels (about 70% of the IMP usually works best for solar direct).

If you need to use a battery to power the controls for the boat (seperate system so the panels would not be hooked to the battery) charge it between rounds.

WWW

[overtak3n]

Hmmm, then thinking out of the box here, what if you used a DC-DC converter like the Samlex SDC-60 to convert the high voltage of the panels in parallel down to the 12V motor? It would do the same as an MPPT, drop the voltage output and raise the current, but would be real time to the motor instead of charging the battery. I suppose you could have the battery on standby in case it's a rainy day during the race (always seems to work out that way).

On first thought I thought the motor would work pretty much like a PWM controller, drop the voltage down to 12V and use the maximum solar panel current of 8.23A, so it wouldn't be damaged or burned since it can draw a lot more than 8.23A, but is limited to 8.23A. If more current was available it would probably be bad for the motor. I'm not sure if that is correct though. On second thought, if I used a converter the motor will be able to go faster.

If using a converter.. if an MPPT had load terminals can it be used like a converter for the motor as well. If that's not possible, maybe wire a converter such that it can both power the motor and deliver charge to the battery through a PWM controller?

But then again, I still need to figure out the costs because that converter sure looks expensive.

Thanks for all the help I received!

[bcroe]

Hmmm, then thinking out of the box here, what if you used a DC-DC converter like the Samlex SDC-60 to convert the high voltage of the panels in parallel down to the 12V motor? It would do the same as an MPPT, drop the voltage output and raise the current, but would be real time to the motor instead of charging the battery. I suppose you could have the battery on standby in case it's a rainy day during the race (always seems to work out that way).

An output regulated switching converter won't work like an MPPT. If the motor needs more power
(at 12V) than the panels are generating, it will pull the panel output voltage down, well below Vmp,
and a buck converter will probably end up being a straight thru short.

Short of an MPPT, I'd suggest a switcher which regulates the INPUT voltage to be Vmp. That will
mean the panels are delivering their best power, at whatever output voltage matches up. Bruce Roe

[Bucho]

The battery constraint is limited to 15Ah.

Does it need to be lead acid?

[overtak3n]

Does it need to be lead acid?

Nope, but it must be marine quality sealed, which I assume any sealed battery pretty much is.