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Which Alternator should we use?

PostPosted: Mon Aug 30, 2010 1:52 pm
by jme521
We have an electric car, which already works, but the batteries run out of power within a one hour period. We have a Honda Horizontal OHV Gas Engine with 50cc's and want to hook it up to an alternator to create a power generator to charge our batteries while we drive but do not have an alternator. We came across your website and had some questions about the graphs and what they meant. Our motor has 2 ft/lbs of torque at 4500 rpm. We would like to know what kind of torque it takes to turn one of your 24 volt alternators before we buy one.

Re: Which Alternator should we use?

PostPosted: Mon Aug 30, 2010 6:13 pm
by Coulomb
What battery voltage are you using?

Re: Which Alternator should we use?

PostPosted: Tue Aug 31, 2010 1:23 pm
by jme521
Two 12 volts hooked up in series for 24 volts

Re: Which Alternator should we use?

PostPosted: Tue Aug 31, 2010 3:01 pm
by Coulomb
The engine may have 2.5 HP, but virtually no torque. Converter to electrical energy, 2.5 HP equals 1860 Watts. At 28.8 Volts charging, the current is about 64 Amps. But we have to introduce conversion efficiency which is about 30% for a small frame, 40% for a typical large frame alternator, and about 70% for our hybrid permanent magnet/field coil unit.

Translated to current respectively you get 19A, 25A, and 45A. However, the engine may not have enough torque to push through the cogging of the permanent magnets on our hybrid unit, so the safest bet would be the #4109 unit mated with an SAR V3 regulator that allows you to dial in the current produced so it doesn't stall the engine.

Don't take any of these numbers as absolutes. There are a lot of variables in making an engine/alternator unit.