In an answer to my own question about the AC power required to start charging a low power pack I purchased a Reliance AmWatt meter from Northern Tool. This AC digital meter is only 25 bucks and measures AC current plus it sorta measures power in watts. This inexpensive meter, or one like it, is probably what most people would use when measuring the power requirement. Anything better, that would take power factor and distortion into account, would cost a lot of money.
The current accuracy given is + 5%, however, the power in watts, or more correctly in VA, assumes 120 VAC and always multiplies the current reading by that amount, to display watts. I made several measurements where I also used a good digital rms voltmeter to simultaneously measure voltage while reading the current. I wrote down the current, voltage, and wattage readings. Since I don't know the actual power factor, I'm going to make an assumption that it is unity (which it probably isn't) so even though we are talking VA I'll show it as watts.
Here are some of the measurements:
ACV Amp. Displayed power Calculated power (V x A)
121.6 8.9 1072 w 1082 w
121.3 8.8 1055 w 1067 w
121.4 8.8 1062 w 1068 w
113.4 9.2 1107 w 1043 w
122.0 6.5 778 w 793 w (LED indicator on charger had dropped to next lower position)
So one can see that the direct reading meter is not far off, if the AC line voltage is close to 120 V. However, if it is low then the meter reading would indicate a power level higher than what is actually being drawn. I would say that a good approximation, or "rule of thumb" would be that the S/DS charger requires 1KW when starting initial charge, after a ride. So a solar power source or gas generator would have to have as a bare minimum a 1000 watt rating. If the actual power factor is leading or lagging by very much then the maximum AC current rating of the source would have to be considered also.
Are you asleep yet?
trikester
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Topic: AC power requirement measured (Read 1008 times)