Author Topic: DC Motor as a generator (Read 3049 times)

paulrogers6 · « **on:** September 10, 2009, 12:10:48 PM »

Dear All

Am I right in thinking that with a DC motor as a generator that the direction the generator turns will determine which output is +ve and which is -ve?

If so which way does the generator turn in relation to the blades, eg is the thin edge of the blade the leading edge or the thick edge (I guess the thin edge is the leading edge but would like confirmation to be on the safe side)? Do plastic drainpipe blades operate the same way?

The reason I ask is that I assume the batteries must be wired up so the +ve output from the genny is connected to the +ve side of the battery bank and -ve to -ve. Is that correct?

Thanks

Paul

ghurd · « **Reply #1 on:** September 10, 2009, 06:53:52 AM »

The rounded edge is the leading edge. The blade turns toward the rounded edge.

The thin edge is the trailing edge.

Pipe blades turn away from the straight edge that is touching the hub.

It does not make much difference which direction most large DC motors turn, as long as you can tell which is +VE when the wind is blowing.

"I assume the batteries must be wired up so the +ve output from the genny is connected to the +ve side of the battery bank and -ve to -ve. Is that correct?"

That is correct.

Some motors can make more power turning one direction over the other. It is usually not much of a difference in the things I tried. Other people found it makes a larger difference in some of their motors.

G-

Flux · « **Reply #2 on:** September 10, 2009, 07:01:22 AM »

Any more stupid questions?

"Am I right in thinking that with a DC motor as a generator that the direction the generator turns will determine which output is +ve and which is -ve?"

Yes

"If so which way does the generator turn in relation to the blades, eg is the thin edge of the blade the leading edge or the thick edge (I guess the thin edge is the leading edge but would like confirmation to be on the safe side)? Do plastic drainpipe blades operate the same way?"

Blades rotate with a blunt leading edge, the trailing edge is the sharp one. PVC blades probably don't have much of a sharp or blunt edge but the angle will determine the rotation.

For a dc machine run it in the wind and check the polarity of the output with a meter. Connect the lead that is positive to the battery positive and it will sort itself out. Without a diode it will motor in the direction that the wind turns it so just fit a diode to block the motoring and it will be in the right direction for charging.

Flux

paulrogers6 · « **Reply #3 on:** September 10, 2009, 07:22:08 AM »

Hi Guys

Many thanks for the comments. I thought I knew the answers but wanted to check before I broke or burnt anything out.

Perhaps I should've reworded the questions:

For a DC motor the output of the generator has nothing to do with which lead is marked +ve or -ve but is entirely determined by the direction in which the generator turns. Since the generator must be correctly connected to the battery bank then one must know which direction the genrator is going to turn. The only way to to that is to orient the blades so that the thick edge faces in the correct directin for the generator. Sound about right?

Again many thanks.

Regards

Paul

PS - Flux - The answer is yes - there'll probably be many more stupid questions before I'm done :-) Thanks for your patience!!

Blutoy · « **Reply #4 on:** September 10, 2009, 10:33:43 AM »

Woa, Please be nice. Flame wars and rude comments are NOT tolerated here, and the offending comments will be deleted immediately. Keep in mind that sarcastic and cynical comments that you might make in person (with a smile on your face!) often appear to be very rude on a discussion board... Newbie

TomW · « **Reply #5 on:** September 10, 2009, 10:47:20 AM »

toy;

And your point is?

paulrogers6 · « **Reply #6 on:** September 10, 2009, 11:54:09 AM »

Hi Blutoy/All

Sorry it wasn't meant to be rude or sarcastic. I know I ask stupid questions (tho' I really do need the answers) and was genuinely thanking Flux for his patience.

Regards

Paul

Blutoy · « **Reply #7 on:** September 10, 2009, 12:11:48 PM »

toy;

And your point is?

Any more stupid questions?

Blutoy · « **Reply #8 on:** September 10, 2009, 12:17:47 PM »

I know what you mean, at least you asked them in the right forum. I have questions that I would like to ask, but hate rejection or being belittled.

TomW · « **Reply #9 on:** September 10, 2009, 12:22:01 PM »

Paul;

Which is my point. You did not seem offended and flux is apparently immune to being offended and got your answer so its nobodies business beyond stirring the pot.

Hope you got the answer you need. Sometimes the details are not easy for those with no background.

Tom

clflyguy · « **Reply #10 on:** September 10, 2009, 12:48:08 PM »

Hhhmmmm... Very unusual.. Paul, I think Bluetoy might have been refering to Flux's comment about "any more stupid questions" rather than anything you wrote, as I reread your stuff several times and could find nothing offensive.

Perhaps Flux is just having an off day, as that is not his usual style, and even if it were he would most likely be tolerated due to his continual help to everyone and the incredible depth of knowledge he brings to this board.

Bluetoy- My friend, don't you know the unspoken rules? Well then, I shall break the code of silence and say it out loud.. I am afraid that you are still too new here to point out to ANY of the plank owners an error (or perceived error) on their part. I realize that what you posted was cut and pasted straight from the posting rules but, you know...... Anyway, that's why TomW jumped in with his little unnecessary & sarcastic contribution (also a plank owner). Any where else and he would be labled a cyber bully, but because he is a doer and not a talker, plus some form of admin on this board, (this will probably be deleted before half a dozen people get to read it) he gets to behave like the north end of a south bound horse pretty much whenever he pleases. So, I hope I have been able to clear things up for you somewhat. By the way, Google search Zubbly (RIP), as he was and still is the King of Motor Conversions

Blutoy · « **Reply #11 on:** September 10, 2009, 12:56:10 PM »

You are correct, sir.

Flux · « **Reply #12 on:** September 10, 2009, 03:43:37 PM »

Yes it was my fault. I regretted it as soon as I posted the comment.

I had just answered 2 questions about mppt converters and grid tie inverters, all of which are expensive and complicated equipment and used wrongly can be destroyed in seconds. I would not really expect newcomers to be dealing with them without some real experience. When I realised that these expensive things were being fed with a toy dc windmill with plastic pipe blades I was a bit thrown off guard.

DC motors and plastic blades are really very much a beginner project and if this was the first question I met I would have treated it differently. I know we all have to start somewhere but I really don't encourage people to start connecting expensive electronics to a wind turbine as a beginner project without doing a great deal of study.

If the questions came at different times I would have been happy to answer each on its merit but It worries me that someone would spend money on expensive electronics to connect to a tiny windmill that at best will only produce a 100 or so watts. Even if done satisfactorily the pay back time would be very long indeed and at worst the whole lot could be fried in seconds.

Try to start small and gain experience or do a great deal of study if you want to go in at the expensive end of the market.

I should have made this point at the beginning rather than making the point about more stupid comments.

Flux

paulrogers6 · « **Reply #13 on:** September 11, 2009, 01:41:02 AM »

Hi Guys

Many thanks for the replies etc. As I stated before I know I ask (what may seem to some) stupid questions but I appreciate the fact that people take the time to answer (on lots of forums they'd just ignore the posting) and ultimately I get the answers I require.

You'll appreciate that there's a lot of info out there. I've read Hugh's book and followed the forums and so on and so on, but even then I end up with so much info and often still end up with (stupid) questions like why won't this work eh?

As Flux says a lot of the equipment is expensive and I while I'm trying to start of simple I really don't want to end up having to go out and buy all new kit in six months time when I could've just bought something that'd do both jobs. At the same time I don't want to waste my time/money by blowing something up.

Flux's last comments were exactly what I was looking for (which is also what he'd kindly said in response to my other postings) eg that for this level of setup I'm best off not wasting my time ("It worries me that someone would spend money on expensive electronics to connect to a tiny windmill that at best will only produce a 100 or so watts. Even if done satisfactorily the pay back time would be very long indeed and at worst the whole lot could be fried in seconds."), or my equipment for that matter.

I'm too old (and have asked too many stupid questions) to be insulted by sarcasm, implied or otherwise, and hope I haven't offended any one else (it seems not, thankfully).

Again many thanks for all the replies, I have the answers I needed.

Regards

Paul

gotwind2 · « **Reply #14 on:** September 11, 2009, 09:11:09 AM »

Paul.

If you are starting out, you may want to take a look at my mini 12" wind turbine, good fun and learnt a lot.

http://www.gotwind.org/diy/12-inch-mini-turbine.htm

Ben.

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