solar controller

System · July 2006

Hello,

I am looking to purchase a used solar controller. I am a high school student doing a science project, building a solar cart/bike. My theme is to build it from used materials. So, I am looking for a used 36 or 48 volt controller to be used with the solar panels I have already obtained. I am currently building the bike and it should be completed this month. Once complete I plan to enter it in solar races and exhibit it at science fair competitions around the county. My results will also be posted on my website www.solarcarscience.com along with links to people who have gotten involved in my project. I currently attend Camden Central High school and will be entering the 11th grade this fall.

Thanks in advance for any advice or assistance you will be willing to provide,

Jesse Clifft
2495 Old Hwy 70 East
Camden Tn, 38320

crewzer · July 2006

Re: solar controller

Jesse,

36 V and 48 V controllers are available, but they're not as plentiful as are 12 V and 24 V models. Also, some additional information about your project's soar energy system architecture would help us help you:

(1) Are you looking to connect a PV array to a battery bank at the same nominal voltage (i.e., a "36 V" PV array to a "36 V" battery bank, or a "48 V" PV array to a "48 V" battery bank)?
(2) Or, are you looking to connect a higher voltage PV array to a lower voltage battery bank (i.e., a "48 V" PV array to a "36 V" battery bank)?
(3) What is the expected output current from the controller to the battery bank?

Sounds like a fun project!

Regards,
Jim / crewzer

System2 · July 2006

Re: solar controller

Yes, I am going to use a battery bank.
I am using solar panels from VW. They are the little trickle chargers VW uses to maintain battery charge during shipment of the cars.

They had a small cig adapter that reduced the output down to 13.8v, 5w, 170ma. I cut those off the panels and can wire them together to get the voltage I need. Each panel can put out 24 volts in full sun. I have over 100 of these panels that were donated by VW dealers. I figure I will wire sets three together , then wire the sets of three together to get enough voltage to supply a 48 volt system. I don't think sets of two will be enough to supply a 36 volt system but I will know more when I can get a charge controller and can test it out to determine how many panels I will actually need.

I am going to use a scooter motor and control system to drive the bike I am building. I have found a 36v-1000w motor and a 48v-1200w motor and control system for each so I am flexable. I am waiting till I get the controller (used) and I will then buy the correct drive system to match the charge controller.

My cart/bike is made from 2, 10 speed bikes striped down and mounted side by side. I have an exercise bike seat that is mounted between the 2 bikes at a lower level than the original bike seats. Once I get the controller and determine how many panels I can mount to the bike I plan to build an enclosure for the bike and mount the panels to it.

niel · July 2006

Re: solar controller

do not confuse the open circuit voltage of those pvs with the nominal working voltage. each of those pvs were to provide for a 12v battery on a trickle basis so for 2 batteries in series it's be 2 pvs in series/3 batteries in series 3pvs in series/ 4 batteries in series 4 pvs in series. i hope you don't think the pvs will be enough power to keep this going with motors as large as you've got. all of your pvs together would be about 500w so this is a situation of charge it while it sits and then go later after it's charged. venturing too far away without the ability to recharge the batteries could windup making you and your scooter stranded someplace.
your batteries also need to provide a great deal of power to run these huge motors so i would suggest going with maybe a 300-400w motor instead and this would still be roughly 1/2 horse power.
doing a project such as this seems simple on the surface, but there's much to do and consider. some of those considerations may be how to gear down and speed control.
good luck.

System2 · July 2006

Re: solar controller

Yes, I had looked into a smaller motor but I do not think a 400-500watt will be large enough to pull the bike, if it could than I could get by with a much less expensive charge controller, say 24 volts. I did not build it as a rider assist bike due to the fact I want to test the run time/distance. Rider assist would skew the test results and I want to see how effective the used materials I can aquire are. That is the theme of the project. A solar bike/cart that is assembled from used materials. If I had deep pockets I could have built a go kart type bike and purchased preassembled panels and an ETEK motor and control system. But since this is a simple high school science project I am going to keep my costs low and build from used materials. I thought someone that visits the forum might have a 36 or 48 volt controller they might be willing to sell. I realize I will only get a given amount of power from the solar array I build, that is OK. At least I will be able to see how effective or ineffective the panels are and if the overall project will be a success. It is the science behind the project that I am after, not if it will run cross country. But maybe across the county. HAHAHA
Again, I am looking for a 36 or 48 volt charge controller that is used, to comply with my project guidelines.
Thanks

crewzer · July 2006

Re: solar controller

Jesse,

OK... Great info, both directly and indirectly...

There arn't many 36 V controllers. However, the Morningstar TriStar, which is easily user-configured for 12 V, 24 V or 48 V operation, can also be configured for 36 V operation. Check the owner's manual. This controller, which is avalable in both 45 A and 60 A versions, may therefore be worth your consideration.

A smaller 48 V alternative is the Morningstar ProStar 15M-48V. This is a 48 V only controller that can handle up to 15 A. I suspect that finding a used model of either will be difficult. I saw none on E-bay.

Many challenges await as you tackle your project. I wish you good luck, and feel free to come back anytime with more questions.

Regards,
Jim / crewzer

System2 · July 2006

Re: solar controller

I agree, It will be difficult. In fact I've been looking for one for almost a year now. The ones I've run across ended up being almost as expensive as a new one.

niel · July 2006

Re: solar controller

jesse,
i have an idea. why don't you sell a few of your small pvs on ebay or here and with the money you can buy the controller you wish to have. you will still be able to use the controller after your project is over with along with your little pvs. once bitten by the solar bug you're infected forever so you might as well use them for yourself. you'll really get a good feeling after a storm knocks out the power, but you'll have lights, tv, and other light drawing stuff with an inverter if ac or straight dc if you plan it. i've said it before on here putting it together and paying for it is a pain in the arse, but having lights when the power goes out, priceless.
you could place this into your profile so that it appears at the bottom of your posts. say the pv specs, price with shipping and how to get a hold of you. links are good for some of this too. it may help you in stating it is to benefit you in a class science project. normally advertizing wouldn't be allowed, but you aren't in the business or competition so to speak so there's no problem. see forum rules.

System2 · July 2006

Re: solar controller

Thanks for trying but I can't sell the panels cause they were donated by VW dealers and I need them for the project and as spares.

My biggest problem is just finding a controller that is used that fits my needs. People don't really want to sell one that works.

Frank · July 2006

Re: solar controller

Jesse sounds like a fun project. Just TRY IT OUT and you'll have fun learning.

FWIW, I converted a small m-cycle to 36VDC series motor and with me onboard it weights 475#. 25A draw i.e. ~900 watts can push me along at 30 mph pretty easily on the flat. A lightweight machine wouldn't need that much; my bike has crappy old tires and a fair amount of rolling resistance and frontal area.

Could you try to make your own controller by using some type of voltage sensitive relay? I'm not an electronics guy but a small circuit could drive a relay or transistor to open the charging circuit for some period of time. Modern controllers use a PWM scheme i.e. high-frequency switch to modify the voltage the batteries "see". Maybe you don't need anything this sophisticated.

System2 · July 2006

Re: solar controller

Yes, I have looked into building a simple dumpload controller but it kinda gets away from the used theme of my project but I think the science fair judges would really like the project more if I did build my own controller. I went to the local Radio Shack and you would have thought I was talking Greek when I started asking about the parts I would need. I think They are getting away from their roots. Now it is all cell phones and remote control cars. Anyway, Thanks for the support. I have another question for the group, When I get ready to mount these glass solar panels what type of surface would you suggest I mount them to. I am looking at using plexiglass so It will allow people to see inside the vehicle to see how the car works. I plan to drill large holes in the plexiglass to help the heat disipate away from the panels and if I do go with a dump load controller I could mount an electric fan to kick on when the batteries are full and the sun is providing more power than I need. This will help keep the panels and me cool and solve the problem of having somewhere for the extra power to go.
I was also looking at using thin plywood to mount my panels to. Any idea?

halfcrazy · July 2006

Re: solar controller

Jesse you dont need anywhere for the power to go you just need to disconnect the panels from the batterys at a certain voltage. as for the plywood maybe something as simple as 1/4 luan underlayment used to go under vinyl flooring? it isnt real strong but is flexible to a point may work good for you?

System2 · July 2006

Re: solar controller

Yea,
I could just use one blocking diode and charge the batteries straight from the panels, and switch off the panels manually when voltage reaches full capacity to prevent damaging the batteries by overcharging. I had also given the thought to the idea of not using batteries at all. Since I am Matching motor capacity up to panel capacity I've considered running straight off the panels. But no sun no go. I don't know if that would be a good idea or not? What do you think?

I've talked to the motor guru's and they say I can lower voltage without damaging the motors but should not increase voltage above their rating. I have been studing the idea of getting a 36 volt motor and running it off my 24 volt panels. The motor will be rated high enough to allow me not to have to worry about over current and I can then run to the max speed allowed by the sun. It would be a true solar car. Not stored energy in batteries. The sun would truly determine how far I can go, then to add some comparison data to the project I can operate the bike/car off of batteries charged by A/C and then charged by the solar panels with panels turned off, then running off the batteries charged by the solar panels and the panels supplying power during the drive.

I need a asphalt course to follow to have a uniform course. I also am looking at doing the study under different sun conditons. Full sun, partially cloudy and overcast and use that to compare the data also. If I can get it done quick enough I can get some summer/fall/winter data also.

I did the first stage of the project last year. I used the VW panels wired together to charge a 12 volt battery, then used the battery to supply power to a 6 volt remote control car thru an inverter. It took 4 panels to equal the power supplied by a A/C outlet. This means the amount of power the 6 volt toy battery used equals the amount of power based upon the run time of the battery operated toy car.
I started out by getting a base run time from the A/C outlet after the battery was on the charger 1 hour, then charged from the battery with no solar panels attached. Then with one panel, two panels, three panels and finally 4 panels. In each test I measure the run time of the car and the beginning and end volatge of the 12 volt battery while charging the 6 volt battery from an inverter. One varible was A/C voltage was 118 from our home outlets and 105 volts from the inverter. There was also some power loss due to the charge controllers of the panels reducing the power to 13.8v and the inverter converting it to 105 volts. But the final outcome was it took 4 panels to equal/maintain the amount of power the 6 volt battery charger was pulling on the 12 battery, thru the inverter.

Each test drive would be be timed, distance recorded and beginning and end voltage of the battery recorded. I need to figure out how to determine the amount to power supplied from the panels in KwA for each test drive. and I plan to record time of day, date, weather conditions and any other varibles that might be a factor. Like wind speed, wind direction, outside air temp and maybe even battery specific gravity.

Since I am having so much trouble finding a 36 or 48 volt controller, I have been looking at 24 volt controllers today. Again the motor guru has a motor that might be able to fit my power needs. So, I guess I am looking for a used 24 volt charge controller also.

niel · July 2006

Re: solar controller

i hate to point these out but,
1> 500w of pvs isn't power matching a 1000 or 1200w motor to run independantly.
2> if the pvs were enough to run it i doubt you have the room to mount them all on your scooter/vehicle.
3> going without a controller and removing all of the pvs prior to exceeding voltage levels will bring the batteries roughly to about 80% charged unless you wish to remove individual pvs as it continues to reach the voltage max point. that would get the remaining 20% into the batteries, but what a babysitting job that'll be.

halfcrazy · July 2006

Re: solar controller

what about something basic like a xantrex c-35 charge controller they arent to pricey can be had sometimes on ebay also?

System2 · July 2006

Re: solar controller

Hey again,
Yes if I decide to go without a controller I would have to match motor capacity to my array output. But, I think it would not be a long term solution to my power controller issue. I'm still looking for a used controller. Most on e-bay are new and the used ones I've seen are being sold by someone who knows almost nothing about the controller because they got it at a auction, from a friend, from a home renovation they were working at and last but not least they purchased it used and never got around to using it themselves. I guess I am afraid to buy one that has no background info and since I have very little funds I'm afraid to waste my money on a controller that does not work.
I have also given some thought to using a 12 volt charge controller and charging a 12 volt system. Then running a A/C 1/2 hp variable speed motor my dad has thru an inverter. It also has reverse. It would save me alot of money and time but I am afraid the motor would not be strong enough. The biggest problem is going to be getting the car to start moving from a dead stop. Do you think an A/C motor would work in a solar car application?
I spoke to a local inventer who drives around town on a bike powered by a pusher. It has a small gas motor drive system. 160 miles per gallon. He said I should need around 1 1/2 hp motor to get it to start moving own its own.

System2 · July 2006

Re: solar controller

Caleb Schmidt of Sun Find Solar Products http://www.sunfindsolarproducts.com/ was kind enough to donate a used solar controller to the project. It is a Xantrex C-35.
I also posted a bunch of pictures on my website www.solarcarscience.com of the solar bike I am building. The frame work was completed today and I hope to complete the solar panel mounting brackets next Sat. I am currently also looking for about 4 sheets of plexiglas. I want to go with clear to allow the public and science fair judges to be able to view the internal working of the bike. I am still trying to keep with my project theme of building the bike from used, recycled, scrap materials. So, If you have an idea where plexiglas can be obtained that may be used or factory scrap please send me a e-mail.

niel · July 2006

Re: solar controller

that's great news jesse and very nice of mr. schmidt to donate that to you. that's another obstacle out of the way now. btw your hair looks like mine did at your age. good luck and keep us posted.

solar controller

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