On Sat, 26 Mar 2005 20:48:42 -0800, Stephen Trapani
wrote:
Peter Bennett wrote:
Forget about electric heat - it just isn't feasible with the batteries
you have.
Yeah, I've got a Force 10 propane. I'll get that working soon,
hopefully. I just thought maybe I could use the floor electric heater in
a backup situation if I needed to, on the 850watt setting if I need to.
Looks like it won't be good for much else.
If I recall correctly, Group 27 deep cycle batteries are rated at 100
- 110 Ampere-hours, so you have about 200 AH capacity in total. It is
generally recommended that deep cycle batteries should not be
discharged more than half-way, so your usable capacity it only 100 AH.
Your 850 watt heater will draw about 7 amps at 120 V, and the inverter
will draw perhaps 75 - 80 amps (allowing for inverter inefficiencies).
The AH rating of a battery is calculated assuming the battery will be
fully discharged in 20 hours - for your 200 AH battery bank, this
would mean a 10 amp discharge current. If you discharge the battery
at greater than the 20 hour rate, the total energy you can extract is
reduced. Your heater would require about 8 times the 20 hour rate.
The table I have for this only goes up to 5, where the effective
capacity is reduced to 72%. You could probably expect about 60%
capacity, so you could only run the heater for about 40 minutes. (and
then you might have trouble starting the engine.)
The microwave, power tools (and possibly an electric
kettle) are OK, as they are short-term loads, and the total
ampere-hours used by them should be fairly low. The TV and boom box
would be on for longer periods, but are fairly low draw, so may also
be OK - but I would definitely want a separate starting battery!
So in order to do without the seperate starting battery I can manage
with careful planning, etc?
Stephen
Yes, maybe...
You should look at the current required for each device you want to
use, and how long you will use it, to determine the ampere-hours you
will consume between recharges. A battery monitor like the Xantrex
Link 20 can help you monitor the state of charge of your batteries.
I still strongly recommend adding a separate starting battery - it is
valuable insurance in the event you do discharge the house batteries
too far.
You should also replace the stock voltage regulator on the alternator
with a "smart" or three-stage type - this will allow the engine to
recharge the batteries much more effectively than it does now. A
three-stage AC charger would also be a good investment (there may be
one built into the inverter...)
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
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