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Forum Index : Electronics : DC power tools
| Author | Message | ||||
| acid house Newbie  Joined: 22/05/2011 Location: Posts: 5 |
Please be gentle as I know very little about electronics but.............. If I rig up an automotive alternator to give me a 12 volt supply will it be enough power to run a 12 volt cordless drill with the battery pack removed. I want to try and get rid of the idea of recharging batteries as even the top of the range types have a life span and are expensive to replace. I also find the lower voltages safer to use than the plug in the wall type. I suppose the alternator has an ampage output and the cordless drill a minimum requirement but will these be close enough to say drive a screw into lumber. Thanks in advance |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi acid house. How are you going to drive the alternator? Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| acid house Newbie Joined: 22/05/2011 Location: Posts: 5 |
I have a small brook that runs through the back of my house and with a medium sized water wheel say 5 feet and the required gearing I should be able to spin an alternator at a constant speed for as long as necessary. |
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| VK4AYQ Guru  Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi acid house A car type alternator will require a constant load otherwise the internal regulator could burn out, also would require a motor to drive it, expensive to buy, and petrol to run it. A better way would be a 12 volt motorbike battery and a trickle charger or a small solar panel. I have used this method and a 12 volt drill will run all day on a 7 amp hour motorbike battery, very cheap on ebay, last one I had lasted 5 years it was a gell cell so no leakage. I used a plug pack 1/2 amp charger to keep the battery topped up, but you could also use a battery saver solar panel from the auto shop or ebay. With this setup you could drive screw to your hearts content. All the best Bob Foolin Around |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi acid house OK on the brook sounds like you could run the house on that. You would be better to scout around for a 12 volt generator old type car if possible as they work at much lower speed than an alternator, a couple of batteries and you have a basic power unit for the house. All the best Bob Foolin Around |
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| acid house Newbie Joined: 22/05/2011 Location: Posts: 5 |
So why do I need any batteries? If I have a constant supply of power for my alternator/generator and its free why include a battery pack. I dont want to power the house (not yet) and if I do it would be with a full power AC generator direct to the house wiring. I dont think this will require a room full of batteries so why with DC. For now I just want to power a cordless drill direct........Any ideas? |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
acid house You need a battery to stabilize the voltage otherwise the voltage may be to high for your drill and burn it out, you do not require a room full of batteries only one 12 volt one. Have a look at some of the things you can do with a home grown system, as it is possible to minimize the use of a generator and save money, unless you have too much of that. All the best Bob Foolin Around |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Yeah Bobs right, a car alternator needs a battery connected to work properly, its designed that way. Without the battery, it will either not work at all, or its output will be jumping all over the place and likely fry your drill. You only need a single small rechargable battery, like a motorbike battery or gell cell. Like Bob said, with your alternator running in the creek, you can drill holes all day. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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mac46 Guru Joined: 07/02/2008 Location: United StatesPosts: 412 |
I agree with Gismo and VK4AYQ...I run my 12 volt cordless on a lawn mower battery hooked up by an old drop cord with battery clips on one end, runs all day with no problem. It's a life saver on the farm when I'm too far away from electric power. The drill is so old that I can't get battery's for it. .....Mac46 I'm just a farmer |
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| acid house Newbie Joined: 22/05/2011 Location: Posts: 5 |
Thanks guys It seems the battery is unavoidable. It will just be a pain if I use the drills for grinding or drilling for long periods. The batteries will no doubt discharge faster than I can charge them so it’s back to back up batteries and changing over regularly.  |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Yes it is. Perhaps you do not grasp the fact that to get *any* voltage out of a modern car alternator you first have to supply its field winding with a voltage - usually from a battery. The alternators output & electronics will then keep this battery charged and also supply the power to its field winding but the battery *must* remain connected. It does not have to be a big battery as was mentioned above. Excess power available from the alternator is yours to tap off to power your drill etc, all at the battery charging voltage (around 14V DC). Of course, you cannot get more power out than you provide to drive the alternator in the first place so your water wheel must be up to the job. Also, if you look under a car's bonnet you'll see that the pulley on the crank is about 3 times as big as the pulley on the alternator. So, with the engine running around 2000RPM the alternator runs at about 6000RPM, a speed where the alternator begins a decent charge. Perhaps a tad fast for your waterwheel, this would need multiple pulley speed step ups. Klaus |
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| acid house Newbie Joined: 22/05/2011 Location: Posts: 5 |
As apposed to not grasping the intricacies of an automotive alternator, I had no idea about their workings, hence the original post. I have grasped the general principals now so thank you for your information, it’s very much appreciated.. 6000 r/m is achievable from my water wheel design but I may go down a different track now. How about a 230AC generator working off the wheel and a 12 volt transformer to feed the drill. Again my mechanics are ok but my knowledge of electronics is limited. Can I get or make a transformer with enough clout to run the drill 'direct'? Electricity!...........Dont trust anything that can run up hill!  |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Yes mate, it can be a frustrating subject if you did not have formal training with electricity  .
230V AC generator can be driven off the wheel but remember the AC frequency (50Hertz in Oz) is directly dependent on the shaft speed of the generator and its number of poles. And the 12V transformer only works well near the 50Hz frequency... Transformers are made to power whole suburbs so one for a single drill is no problem but, you must first find out the load current (Amps) that your drill draws. Try to borrow an Amp meter if you do not have one, 20Amp range should be plenty. Power your drill from a 12 V battery and then measure the current by placing the meter in *one* lead (like +battery to + meter, - meter to + drill) and see how many Amps it draws when you drill the biggest hole you are planning to drill. This gives you a figure to work with. You seem to start a project the same way as I do, try the most complicated way first  .
If I were in your shoes I'd use a F&P generator (plenty of info on this site about these) or a DC motor (one that has permanent magnet fields) of sufficient Amps to power your motor. Treadmill motors might be right for this. The motor should have a low RPM rating. You need to turn this with your water wheel (motor becomes a generator) at sufficient RPM to generate your required 12V DC. There is a fair bit of tinkering involved, its great fun (IMO anyway..) and a good learning curve. Keep asking questions here Klaus |
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| viatu3 Newbie Joined: 29/11/2011 Location: United StatesPosts: 5 |
Never thought about this but it sounds very interesting. It is definitely true that batteries are very expensive if you need to replace them. I do not own a lot of power tools because I also think that most tools are very expensive and if you do not use them often it is definitely to expensive to buy all of them. Due to this I am using a power rental whenever I need such tools. This is really cheaper and so I do not have to think about the life span of the batteries. |
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