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

[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.

[Bucho]

The battery constraint is limited to 15Ah.

Does it need to be lead acid?

[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

[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!

[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

[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).

[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.

[overtak3n]

So to help you maybe you can provide the full description of what you have been asked to do and why.

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.

[SunEagle]

If the specs say the maximum power current is 8.23A (and short circuit current is 8.81A) can an MPPT really increase the current by lowering the voltage? Will the solar panel be able to generate more current? If the current increases when the voltage lowers, and 8.81A is the short circuit current, I thought the short circuit current is the highest current you can ever get regardless of the voltage. At short circuit the voltage is nearly 0V?
I hope to understand these questions as this is my first time dealing with solar panels so I don't really know how if their currents are limited.

Thanks for all of the responses!

Just to clear things up a bit, these solar panels were given to be used on the competition. Every competitor is using the same panels. After the competition we must give them back. We are restricted to just the 2 panels, no other source of power generation is allowed and we can't use extra panels. The battery constraint is limited to 15Ah. Charging the battery is not a requirement, I was just wondering if it would be possible to charge it in between rounds with these panels.

Thanks again for all of the help and sorry for any confusion.

It sounds like they gave you the panels to use in this project but not necessarily to use them to recharge the battery. Kind of confusing for me.

So to help you maybe you can provide the full description of what you have been asked to do and why.

[overtak3n]

Well said Paul. So it's not that the panels are putting out a lower voltage and higher current, they are sending the 32V 8.23A into the charge controller, and the charge controller is converting the charge controller's voltage output down to about 17V and increasing the current.

I didn't know converters/transformers work that way. Thanks for the info.

The event is providing the equipment and the battery restrictions, but not an MPPT charge controller? Hmmm, trying to find something nice to say about that. Failing.

Haha yup when I figured out about the restrictions I thought it would be harder than I intended. We're constructing a solar boat and using it to race.

What this Posting shows is the lack of good knowledge of solar battery systems by the people putting on the event.

It also reinforces my feelings that the majority of people coming to this forum have preconceived ideas on what solar and batteries can provide in the way of power.

I feel they need to be given good & clear guidance to help them understand that what "they want" may not be what "they need" and the associated costs to build a good balanced system.

I already mentioned it, a charge controller is not required. In this event it's purely solar and pure battery in various rounds. I don't think they lack good knowledge. In fact, I think if they required charging then the restrictions would be different. Hey I'm still learning.

[SunEagle]

Well said Paul. So it's not that the panels are putting out a lower voltage and higher current, they are sending the 32V 8.23A into the charge controller, and the charge controller is converting the charge controller's voltage output down to about 17V and increasing the current.

The event is providing the equipment and the battery restrictions, but not an MPPT charge controller? Hmmm, trying to find something nice to say about that. Failing.

What this Posting shows is the lack of good knowledge of solar battery systems by the people putting on the event.

It also reinforces my feelings that the majority of people coming to this forum have preconceived ideas on what solar and batteries can provide in the way of power.

I feel they need to be given good & clear guidance to help them understand that what "they want" may not be what "they need" and the associated costs to build a good balanced system.

[Amy@altE]

Well said Paul. So it's not that the panels are putting out a lower voltage and higher current, they are sending the 32V 8.23A into the charge controller, and the charge controller is converting the charge controller's voltage output down to about 17V and increasing the current.

The event is providing the equipment and the battery restrictions, but not an MPPT charge controller? Hmmm, trying to find something nice to say about that. Failing.

[paulcheung]

If the specs say the maximum power current is 8.23A (and short circuit current is 8.81A) can an MPPT really increase the current by lowering the voltage? Will the solar panel be able to generate more current? If the current increases when the voltage lowers, and 8.81A is the short circuit current, I thought the short circuit current is the highest current you can ever get regardless of the voltage. At short circuit the voltage is nearly 0V?
I hope to understand these questions as this is my first time dealing with this.

Thanks again for all of the help and sorry for any confusion.

The MPPT controller act like a step down transformer, it convert the high voltage low ampere current to lower voltage higher amperes current. so if you have 30 volt and your batteries is 12 volts it will double the charge current on the battery side, if you have 8 amps in then you will get over 16 amps out to 12 volts.

[overtak3n]

An MPPT will convert the voltage down, and in doing so, because of ohms law, will increase the current. 20V / 12V = 1.6. 8.23A x 1.6 = 13.16A x 5 hours = 65.8aH. That's 24.3aH more than if you used a PWM.

Amy

If the specs say the maximum power current is 8.23A (and short circuit current is 8.81A) can an MPPT really increase the current by lowering the voltage? Will the solar panel be able to generate more current? If the current increases when the voltage lowers, and 8.81A is the short circuit current, I thought the short circuit current is the highest current you can ever get regardless of the voltage. At short circuit the voltage is nearly 0V?
I hope to understand these questions as this is my first time dealing with solar panels so I don't really know how if their currents are limited.

Thanks for all of the responses!

Just to clear things up a bit, these solar panels were given to be used on the competition. Every competitor is using the same panels. After the competition we must give them back. We are restricted to just the 2 panels, no other source of power generation is allowed and we can't use extra panels. The battery constraint is limited to 15Ah. Charging the battery is not a requirement, I was just wondering if it would be possible to charge it in between rounds with these panels.

Thanks again for all of the help and sorry for any confusion.

[Amy@altE]

Thanks Paul, yes, MPPT. Fixed post. Making myself more coffee now.