Converting golf cart to solar

System · April 2007

I run a science club for girls (You can check our work at www.badgirlscience.org) and our next project is converting an electric golf cart to solar. We're all learning as we go. It's an old Westchester cart (36 volt system) I have (3) 20 Volt panels (old.. but still working) I understand that I need a charge converter.

Any advice out there on where and what size to buy. Any other advice to consider? I'm a solar newbee....

Roderick · April 2007

Re: Converting golf cart to solar

Sounds like a neat project!

Can you check your panels, and let us know the ratings? Hopefully, there will be a sticker on the back, giving the currents, voltages, and power. Alternatively, if you have the exact model number of the panels, someone here can look it up.

One of the problems you may face will be getting a minimum charging current for your batteries. It will help if you can tell us the make and model of batteries, too.

In general, it's going to take a long time to charge your batteries from any solar that would fit on the roof of the golf cart, possibly weeks. However, having been in a science club before, I understand that non-optimum is ok, this is a show of concept, not a commercial product. My concern would be that the panels you have might not be capable of ever charging the battery bank, a disappointment for all involved. That's where having more information on your equipment will help.

Take care,
Roderick.

crewzer · April 2007

Re: Converting golf cart to solar

Cool Project!

Take a look at some of the links from this Google search . Specifically, this one looks like it might be directly relevant: http://www.solar.unlv.edu/projects/spgc.php

Here’s another search string.

Note that PV modules can get very hot (> 140 degrees F) when exposed to direct sunlight. One of the good features of the UNLV configuration is that the original cart roof was kept in place and it serves as a sort of barrier between the passengers and the hot PV modules.

While on the subject of safety, lead acid batteries can be very dangerous. Shorted batteries can melt metal and cause burns, and the sulfuric acid inside the batteries is also dangerous. Effective safety precautions around the batteries as well as the PV modules will be essential. See this Trojan battery maintenance guide for additional useful information: http://www.trojanbattery.com/Tech-Support/BatteryMaintenance.aspx

Assuming the golf cart uses typical 6 V "Golf cart batteries" like these , the safest models to consider are VRLA types (AGM or gel), as they are sealed and generally will not leak acid, even if tipped or punctured. Here are some examples:

http://www.trojanbattery.com/Products/ProductSpec.aspx?Name=6V-AGM
http://www.mkbattery.com/images/golf8AGC2.pdf
http://www.mkbattery.com/images/golf8GGC2.pdf

Adding to Roderick’s comments:

Once we know more about your PV modules, we can be more specific about a controller recommendation. However, there are very few controllers that are configurable for 36 V. The Outback MX60 is probably the easiest to use, in part because it includes a user selectable 36 V setting, and it accepts a wide range on PV module voltage inputs. Unfortunately, it’s not inexpensive, but OutBack has been known to support educational projects. See the links below for more info:

http://www.outbackpower.com/MX60.htm
http://www.outbackpower.com/pdfs_manuals/MX60_Manual_6_2.pdf
http://store.solar-electric.com/outpowmxmp.html

The Morningstar TriStar controller can be PC programmed for 36 V operation. The SW is free from Morningstar, but you’ll need a PC on which to load the SW and then plug into the controller for programming. Once programmed, the PC connection can be removed. Depending on the PV module specs, the smallest version of the TriStar (45 A) should be more than adequate for your project. See the links below for more info:

http://www.morningstarcorp.com/products/TriStar/index.shtml
http://www.morningstarcorp.com/products/TriStar/info/TS_Manual.pdf ; see page 46, Section 9.0
http://store.solar-electric.com/trts12vochco.html

HTH,
Jim / crewzer

System2 · April 2007

Re: Converting golf cart to solar

i'd recommend staying away from mounting on the roof of the carts. most panels were not designed for the kind of vibrations translated through a cart. if it's an absolute must to mount them up on top, lok into sme kind of vibration dampening materials.

niel · April 2007

Re: Converting golf cart to solar

i'm going to elaborate further with the pvs being mounted on top of the cart. the top of the car already has a roof so to speak and mounting the pvs directly against that roof will cause the hot pvs to not be able to cool down as they need airflow under the pvs. either the roof is cut out to allow the airflow or mount the pvs at least 6 inches above the roof.
on another note is you must make sure the pvs are delivering enough current to charge the battery bank properly. i think in this case idealy no less than 10% of the battery capacity should be delivered. it may not be possible to mount that many pvs that are able to deliver the necessary current so minimumly you want 5% of the battery capacity rating. in either case the power delivered by the pvs in full sun will be measured in days to fully charge the batteries and if the cart is being used the cart will use up the power the pvs are delivering and the batteries will not be receiving a charge.
this is a good project none the less as it will also teach how precious power is in this country of people whom are spoiled as they can flip switches and have all the power that they want for $xx. it will also show the difficulties and problems being faced for solar electric cars and why we don't see them as this is the same principle.

crewzer · April 2007

Re: Converting golf cart to solar

I'm not sure I'd worry a whole lot about roof top vibration for this science project. Many of my PV modules began their service life on top of my camper, where they withstood >4,000 miles of on/off road travel and dozens of set-ups and tear-downs.

On the other hand, I think niel makes a good point about maintaining an air gap between the cart roof and the PV modules -- something like what's shown in the UNLV picture. I was so focused on safety that I forgot to consider module ventilation... :oops:

Regards,
Jim / crewzer

System2 · April 2007

Re: Converting golf cart to solar

I may have a suggestion here. In 1995 I built a solar golf cart. I replaced the factory roof with 3 series connected Solarec 90 watt PV panels The panels were mounted together with angle aluminum rails on each side, and bolted to the original roof support posts. These Solarec modules were designed to charge batteries directly without a charge controller. Each panel consists of 2 parallel sets of series strings of 33 cells each instead of the 36 cells strings in typical PV panels. I installed an amp guage and a digital voltmeter to keep track of the batteries.

These panels were used on many of the old traffic control trailers used to warn drivers of construction zones. These old trailers are damaged and/or retired quite often, and can be obtained at surplus sales, or even for free in some instances for hauling the whole mess away for the companies. A few well placed phone calls can turn up one or more of these.

While the lower than normal output voltage can be a problem with traditional solar power systems, they really work well in this type of application. I kept this golf cart parked in the sun, and during the next 2 years that I used it, I never had to plug in the grid powered charger, even though I had one. Additionally, during full mid-day sun, I could throw the battery bank disconnect off, and cruise at about 3 MPH on the solar panels alone. The speed control was not one of those electronic PWM style though, as that would probably have fried without the batttery bank to buffer the PV output. I had kept the original roof, and when I decided to sell off the golf cart, I put the original roof back on and kept the panels.

Bob

Converting golf cart to solar

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