Naked Science Forum
Non Life Sciences => Technology => Topic started by: Airthumbs on 14/06/2012 18:04:54
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I would like to set up a very simple device using the following components.
12volt/24volt car/lorry battery.
Electric motor ((with strimmer wire attached), strimmer is for cutting tall grass and weeds with).
Cable
Solar Panel
Excluding the solar panel my main objective is to be able to run a simple electric motor off one of the above batteries. Is this possible please help as this is the final key....
I have no idea if something like this is feasible but I'm sure it is possible. I have a 12v car battery already.
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I'd encourage looking at battery powered string trimmers.
Black and Decker makes a few. However, I must admit that I have not been impressed with their 12V versions. I've been interested in one of the 36V B&D String trimmers. If you match the voltage of your trimmer with the battery, you should be able to connect it up directly if you wish.
If you wish to make your own, look for an older windshield wiper motor, or other small 12V DC motor.
You can also run your system with an inverter, and normal 110V/220V power. You'll have to match the power requirements with the inverter. Inverters less than 1000W are cheap, but 2000W or 3000W might be better, and can generally be found on E-Bay.
Do you have a solar panel yet?
You can get the flexible panels that are often small with low power generation. Or, you can get larger rigid panels.
A controller?
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Hi there CliffordK,
Thanks for your response..... I do not have an inverter but I would like to stay away from things that might add any weight to the system. I am on the hunt for a windscreen wiper motor and will most likely look from a local scrapyard in the next few days.
I do have a solar panel, it's only a small one but upon testing it does trickle charge the 12v car battery.
The whole system will hopefully fit into the back of my trailer for my bicycle....
I have heard of controllers before, I think they are something to do with organising inputs and outputs on energy collecting devices. ( I think)
I would probably use a variable resistor to control the output but I must get a controller. I'm afraid at present my budget is very limited. However I must get this done.
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There are a few types of controllers that serve a few issues.
At night, there is the potential for some backflow of electricity. The controller will block this. However, a good (Schottky) diode will perform the same task.
It will also prevent overcharging of the battery. However, you can do so manually, or a trickle charge may not overcharge in some cases.
Some controllers are MPPT (Maximum Power Point Tracking) controllers. There may be some drift of the MPPT of your panels. It will also convert higher voltages to the voltage of your battery system.
You can, of course, also get grid attached controllers with built in inverters, sometimes more efficient than trying some kind of a portable system.
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UPDATE....... So then.... I got a Landrover battery, 12v 85Ah. I had a small electric motor rated at 7A and 4.5 - 11v. Following a conversation with an electrician instead of using speaker wire I used household flex. I connected it up to the battery and it strimmed very very well for about 2 minutes before I could smell electrical burning... anyway that's the end of Prototype Strimmer MK1! I am now looking at a motor rated at 14A 12v. However I think I should find out more about these controllers as it looks like the best solution for managing input and output.
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You might need to include a fan to force air over the motor so it does not overheat. The motor might be drawing a lot more current than you would like if its trying to produce a lot of torque while strimming. Try to measure the current if you can get hold of a meter.
One crude (but quite effective) method of protecting the motor is to put some 12 volt light bulbs in series with the motor. Old car headlamp bulbs will work - you might need several of them in parallel for the amount of current you are drawing.
The bulbs act as temperature variable resistors (thermistors). As the current approaches a limit, the bulbs will light up and their resistance will increase dramatically. This limits the power delivered to the motor and prevents it from frying. The bulbs also give you a visual indication that you are overloading the motor.