Subject: [Healeys] Electrical problem NON HEALEY

From: Michael Salter <[email-masked]>
Date: Sat, 30 Sep 2023 11:39:56 -0400

This group has been a huge help in the past and I am wondering if
there are any electrical guys out there who can help me with a DC
electrical problem.

I'm trying to help my BIL with the propulsion system for a 30 ton
wooden boat on our lake.
This 100 year old boat was originally steam powered but in keeping
with modern times it has been converted to electric propulsion.
It is fitted with a 106 volt DC motor
At normal cruise the motor draws 45 amps.
It has eighteen 220 amp hour AGM batteries.
The batteries are arranged in 2 banks of 9 in parallel so each bank
produces 108 VDC
By my calculations ...
For a total of 45 amps each bank would deliver 22.5 amps.
Consisting of 2.5 amps from each of the 9 batteries.
Each battery is 220 amp hours.
Presuming that you want to avoid discharging below 50% the usable
capacity of each is 110 amp hours.
So my calculation for the running time is 110/2.5 = 44 hours !!!!
It only runs for about 20 minutes before the amperage starts dropping
off rapidly.

Are my calculations correct?
If not, where are they wrong?

Thanks

M
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