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Old 20-08-12, 10:54 PM   #11
pauldg
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Bearing in mind I haven't seen how that alternator head is internally configured, I'm happy to state something.

It won't work how you describe.......

If the windings are connected how you say, putting them in parallel will give you 0V, which isn't a lot of good at all.

It may work if you rectify the outputs separately and then parallel them, but then you'll probably run into trouble with the excitation and then regulation - i.e. you won't have any.

Even if all that does work (which I doubt) your rectified DC voltage is going to be a tad on the low side. 55V ac rms rectified is exactly 55V dc. To charge a '48V' lead acid battery pack, you'll need around 58Vdc otherwise you'll be constantly undercharging. On the other hand, if your o/c voltage is too much higher than that you'll gas the buggery out of your batteries - still, worth a few quid weighed in I suppose.

I don't see how you're hoping to get 30-40 amps out of it either - unless you have the box of magic I lost a while ago. If you do have it I want it back 'cos I need it...

I'm all for experimentation if the theory supports it but in this case I'd think you'd be far better off just using the 110V ac and making up a proper battery charger to run on that.
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Old 20-08-12, 11:22 PM   #12
RobSmith
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Quote:
Originally Posted by pauldg View Post
Bearing in mind I haven't seen how that alternator head is internally configured, I'm happy to state something.

It won't work how you describe.......

If the windings are connected how you say, putting them in parallel will give you 0V, which isn't a lot of good at all.

It may work if you rectify the outputs separately and then parallel them, but then you'll probably run into trouble with the excitation and then regulation - i.e. you won't have any.

Even if all that does work (which I doubt) your rectified DC voltage is going to be a tad on the low side. 55V ac rms rectified is exactly 55V dc. To charge a '48V' lead acid battery pack, you'll need around 58Vdc otherwise you'll be constantly undercharging. On the other hand, if your o/c voltage is too much higher than that you'll gas the buggery out of your batteries - still, worth a few quid weighed in I suppose.

I don't see how you're hoping to get 30-40 amps out of it either - unless you have the box of magic I lost a while ago. If you do have it I want it back 'cos I need it...

I'm all for experimentation if the theory supports it but in this case I'd think you'd be far better off just using the 110V ac and making up a proper battery charger to run on that.
There is a 240v / 110v version of this same generator. The windings are configured the same. To get 240v the windings are connected in series to get 110v you connect them in parrallel. I am doing the same with the 110v version to give 55v output.

I will try the alternator at varying speed to see what voltage it gives.
I don't care what the frequency of the output is as it will be rectified to dc.
I will need to get to about 59.2v for normal charge and 62v for the occasional equalising charge. Hopefully it will produce that for me it is not a million miles off 55v.

The generator is a 2.7kva unit. 2700Va / 60volts = 45 amps. I am not sure of the VA and Watts relationship as for some reason va does not equal watts in some situations which is why I am aiming for 30 to 40 amps. I think VA and watts are equvalent on purely resistive loads with a power factor of one. I don't know what I have there so aiming lower.

The reason for going this route is that I am building my own stirling cycle engine to drive this and this sort of size generator is what I want. We are going off grid so will not have mains power available. The planning laws we are going under do not allow IC engined generators. Any conventional battery charger would want a nice consistent input and with a 48v pack to charge they are usually too big for my stirling cycle engine to power. I have to try to balance charging the batteries suitably so they don't die with building a stirling engine big enough but is within our finances. The stirling engine must also match our heat source which will be the waste flue heat from a rayburn or similar so I can't go too big or there will be insufficient heat.
I currently have 1400kg of storage heater blocks which will encase the hot end of the engine and absorb heat while the engine is not running and provide a greater energy store for when the engine is running.

Lots to do

Rob
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Old 21-08-12, 12:36 AM   #13
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I've since seen your other thread in the generators section... If this is the one you are using then yes, you can parallel the windings as it's designed to do it.

As you say, the frequency is just about irrelevant - if you can get it to give you about 65V ac by running it over design speed or altering the regulator then you might just get away with it. I assume you know that Vac(rms)=rectified Vdc (or volts in = volts out) it would be an exact conversion if it weren't for drop over the rectifier etc.

In the same sort of area - is your engine going to be able to produce 4hp? You'll never get more energy out than you put in, and there are always going to be losses.

A well designed (read not conventional) battery charger would take very little more power than direct rectification and could be made to accept a fluctuating input.
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Old 21-08-12, 07:24 AM   #14
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4hp maybe not. I shall get out of it what I can. The cost of the thing starts to shoot up once the design gets beyond what I can cobble together here and I start having to have more and more parts made for me. I am still concidering a multiple cylinder engine as the smaller components would mean I can make more of them here and modification becomes easier too. Man handling the thing becomes easier too. I would loose out on efficency if I did that so it is a trade off.
If I can get it to provide some amps for charging that would be ok but I would rather have 30 or 40.

We are looking to provide about 3 or 4 kwh mains power each day to the home. If the generator ran 24hrs a day that may only be a 125-150 watt trickle (2 amps ish) but from what I can work out the batteries need more current than that to prevent the plates from chemically fouling up. I also want some peace and quiet at night so that reduces its running time to daytime hours and 4 amps or more would be required.

If my engine does not produce the power I am hoping for I will run it for longer. I may need to use a different generator and not this one but I have to try that out. If I can get it to produce 20 or more amps that is great but if it will not then I will just run it at whatever I can get from it and run it for as long as needed.

I have an LG direct drive washing machine motor here too. That is a permanent magnet motor which works as a three phase generator when driven. That would be my next size step down from the Stephill generator. I have had that running fine. It is just not as nice and robust as the Stephill one.

There is a fair amount of guesstimation involved.

Rob

Last edited by RobSmith; 21-08-12 at 07:25 AM. Reason: chnaged a bit
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Old 21-08-12, 09:53 AM   #15
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Quote:
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(snip)The planning laws we are going under do not allow IC engined generators.
A layman's guide to the planning laws relating to this kind of installation would be of interest. My engine shed is 'off grid' - nothing on the scale of yours, just a 60W of PV panels and a leisure battery for lighting, radio and occasional power tool use - I never even thought about any planning implications!

NHH
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Old 21-08-12, 03:31 PM   #16
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A layman's guide to the planning laws relating to this kind of installation would be of interest. My engine shed is 'off grid' - nothing on the scale of yours, just a 60W of PV panels and a leisure battery for lighting, radio and occasional power tool use - I never even thought about any planning implications!

NHH
I would be very happy to be corrected here - but I [I]think[I] this would be something like an 'eco-home' idea...

Running a radio and a drill in your shed is subject to no planning laws.
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Old 21-08-12, 04:12 PM   #17
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I would be very happy to be corrected here - but I [I]think[I] this would be something like an 'eco-home' idea...

Running a radio and a drill in your shed is subject to no planning laws.
Ah, but I also have a wind gen waiting in the wings and (naturally) have considered IC engined back up!

Be nice to know.

NHH

Last edited by nickh; 21-08-12 at 04:21 PM.
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Old 21-08-12, 04:31 PM   #18
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I believe you'll need planning for a turbine (I think it's height related).

There's nothing 'planning' as such for making your own power, unless it involves a new structure.

If you are planning on hooking it up to your house (i.e. mains supply) then it must be wired correctly to turn off in case of grid failure. You also (did?) need authorisation from your supply company.

If you want to have an i/c generator for backup power you must totally isolate your house from the grid if you want power in a power cut - if you backfeed into the grid when it's down and electrocute a line worker I wouldn't like to be in your shoes.......... Turning off the main breaker is not sufficient.
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Old 21-08-12, 04:54 PM   #19
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Ok ok, I was just curious about Rob's statement "The planning laws we are going under do not allow IC engined generators" and would like to hear more from him on the subject that's all. I'm not about to be frying anyone but myself!

NHH
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Old 21-08-12, 07:56 PM   #20
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Ok ok, I was just curious about Rob's statement "The planning laws we are going under do not allow IC engined generators" and would like to hear more from him on the subject that's all. I'm not about to be frying anyone but myself!

NHH
We are going under the Welsh and Pembrokeshire, One Planet Development laws. These don't have any bearing on what we do in our sheds outside of these planning laws and does not apply at all to outside Wales.
These laws allow you to live on agricultural land but you are tied to producing the bulk of your income from your bit of land.
It also comes with other conditions... kids must learn Welsh, must be off grid, little use of cement and building with natural materials etc.
Edit: My Lister CD charging set I shall have as a hobby item and not intended for supplying power... although it might every now and then.

Rob

Last edited by RobSmith; 21-08-12 at 07:58 PM.
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