Reply To: Power supply recommendation for older M1s

[Paul]

Chief engineer (aka spanky) previously posted that battery float needs to be 4V above the 13.9V delivered to the bus. There is about a 1.2V drop across the rectifier, so that means a minimum of 17.9V coming in. Even if you bypass the rectifier it still would need min 16.7 so a 16VDC won’t even start or run an older M1G assuming I understood the engineers numbers right?

Ness confirms older panels need higher voltage to address power stability issues.  The debate is on what voltage is best, but its got to be above 17VDC as that’s the current “replacement” supply that isn’t working on older panels reliability even if the rectifier is bypassed.

AC to DC conversion is not 1 to 1 depending on whether the AC value is peak or RMS. Exactly what the DC equivalent of the original M1G power supply is unclear but its not likely 16-18VDC. Note if I convert based on peak, then 1.4 x 17VAC gives the magic 24VDC number Ness has quoted.

Older panels were not all manufactured the same, so won’t be as efficient as new AC/DC units. I’m talking 10-20 year old units where components are aged and might have been manufactured in different plants (as Ness has hinted at)