# Electronic Circuits and Projects Forum

1. ## Capacitance Calculations

Morning All! I have a home made generator unit based around a 5 1/2 HP briggs engine and 63 amp delco alternator. This system is both setup to supply 12 Volts for charging batteries and is setup to supply 100 Volts DC. I have been experiencing problems with engine stalling with heavy loads and have been looking into the possibility or not of using a cap of suitable size effectively with the alternator? In my quest to find the answers to my question I came across the website known as the "Backshed" the site is dedicated to alternative energy and windpower. I started this topic where I caught the attention of Len who is a electronics engineer by trade. In the process of coming up with the calculations for a suitable cap Len asked that I post the below chart so someone can confirm his calculations as being accurate regarding the size of the cap needed? This is the original discussion on the backshed http://www.thebackshed.com/forum/for...?TID=4448&PN=1

Robert

3. ## Drawing

Hey all! I thought I had uploaded the follow attachment? Did not take for some reason or another.

Robert

4. hi Robert and Welcome.

We have a minor Permission to Post/Access problem to your Thread. I am sure Electromaster will fix it as soon as possible.

Moderation:E

EDIT:

5. Well now that this thread is someplace that everyone can get into....

If you are running a common Delco alternator in a modified setup to get a higher than stock voltage out of it you can also expect it will take a higher than stock input power to drive it at peak loads as well.

Assuming your 5.5 Hp engine is up to snuff its should be able to support around 4100 watts mechanical output peak before it starts dropping off. At 100 volts that would be around 41 amps but most automotive alternators are around 50 - 80% efficient in their normal working range so realistically I would be hesitant to expect much over 20 - 25 amps at 100 volts before you simply run out of engine power.

As far as capacitors go at those power levels they are completely impractical or outragiously expensive for anything more than multi millisecond pulses so a good old fashioned battery bank is the only practical way you will be able get the necessary reserve power for any extended overload period.

6. Can you explain how you're getting 100V from your alternator? Did you just bypass ther regulator? If so, how do you get 12V for battery charging? Thanks!

7. Anyone seen any 1 farad 415 Volt Aluminum caps for sale? I am looking for one similar to a motor run cap in shape.

Brownout, Do to the extreme danger of DC at high voltages I elect not to disclose how I did it. DC is lethal at these voltages unlike AC which is most likely survivable if you were to get zapped. I would look at this if you need a small amount of power? http://www.qsl.net/ns8o/Induction_Generator.html Or simply obtain a portable generator which sometimes shows up on the cheap from Harbor Freight.

Robert

8. Yep they are about \$25,000 and the size of a 30 gallon drum!

9. Brownout, Do to the extreme danger of DC at high voltages I elect not to disclose how I did it.
It's not possible to propose a solution if you don't disclose the details of your design. I don't need a generator, I have all the backup power I require. I find it laughable you think you need to protect us. Anyway, good luck with that.

10. As far as getting 100+ volts out of a common alternator its not that hard. Usually just feeding the rotor with a 12 - 15 volt DC source and spinning it fast enough is all it takes. The other modifications may be switching the windings from a delta to Wye configuration and or stacking the windings in series if its a multi winding alternator.

I have several Leese Neville units that have a stock field configuration of double delta three phase. By reconfiguring them to a single Wye the original 12 volt 150 amp output is now capable of running as a 42 volt 42 amp output with the rotor still being driven at 12 volts. By increasing the speed and lowering the amp draw they can easily run 300 volts at 5 - 10 amps on a load bank.

You can go even higher if you find a multi winding alternator like some of the big 24 volt 140+ amp commercial units are set up with. Many of them will have 3 - 5 parallel windings for each phase so if you stack them all together and you can get some serious voltage and power out of them.

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