RC-Monster Forums - View Single Post - Total non-rc question.

DrKnow65 · 01.06.2011, 12:55 AM

sorry to disagree all, but I am a career mechanic and I've toyed a bit with small engines and no battery. You need to run a battery and here is why... it's a capacitor.

When the system is running on an altenator the battery works to smooth the voltage out. The altenator is actually outputting pulses of power, the volatge regulator is not fast enough by itself to keep every pulse at exactly 13.8v. It reacts to the slightly less fluctuating voltage of the total system (including primarily the battery).

If you doubt, take a oscilliscope to a car and look at the voltage smoothness with the battery plugged in and not. Without the battery you'll see spikes of close to 18v and lows of nearly 11v. The reason you don't see the change significantly is the dwell time of the spikes is very shory (altenator rpm X 3 @ ~30%).

Also in a small engine if the rpm's get low it has a good potential to stall, the lows drop in voltage as the output decreases and the dwell time of those lows are long enough to limit the spark output = stalling.

On a snowmobile you can get REAL stuck if you let off the throttle at the wrong time...

IMHO

	(#7)
DrKnow65 RC-Monster Aluminum Offline Posts: 998 Join Date: Oct 2007 Location: Colorado	01.06.2011, 12:55 AM sorry to disagree all, but I am a career mechanic and I've toyed a bit with small engines and no battery. You need to run a battery and here is why... it's a capacitor. When the system is running on an altenator the battery works to smooth the voltage out. The altenator is actually outputting pulses of power, the volatge regulator is not fast enough by itself to keep every pulse at exactly 13.8v. It reacts to the slightly less fluctuating voltage of the total system (including primarily the battery). If you doubt, take a oscilliscope to a car and look at the voltage smoothness with the battery plugged in and not. Without the battery you'll see spikes of close to 18v and lows of nearly 11v. The reason you don't see the change significantly is the dwell time of the spikes is very shory (altenator rpm X 3 @ ~30%). Also in a small engine if the rpm's get low it has a good potential to stall, the lows drop in voltage as the output decreases and the dwell time of those lows are long enough to limit the spark output = stalling. On a snowmobile you can get REAL stuck if you let off the throttle at the wrong time... IMHO If I could only draw what I see in my head, then afford to build it, and finaly get to play with it...