On Fri, 5 Aug 2005 09:52:36 EDT [EMAIL PROTECTED] wrote:
> In a message dated 8/4/2005 4:22:05 PM Eastern Daylight Time,
> [EMAIL PROTECTED] writes:
>
>
> > I tried one time plugging in the hall socket and got a severe
> > thrashing from the landlady. C'mon lady its 4 amps for crying out
> > loud!
>
> Has anyone tried running a 500W power inverter to run a block heater?
> If you wired your marine battery into the trunk so it could be fully
> charged in the evening when you park it seems that an inverter could
> run your block heater off that battery for a half hour or so, then,
> with the extra cranking power of two batteries you should be able to
> get Gump started in any weather. Good, fully charged batteries
> shouldn't be bothered by 12 hours or so at 20 below.
400 watt block heater
--------------------- = 500 watts from battery
0.80 efficiency of
inverter
500 watts
--------- = 41.7 amperes from battery
12 V
42 amperes x 0.5 hour = 21 ampere-hours
Battery capacities for a W123 300D range from 66 to 100 ampere-hours (see
http://www.varta-automotive.com/pmd/searchByApplication.do?presetModelline=571&modelline=571&manufacturer=74&presetManufacturer=74&modellinetype=417&presetApplication=PKW&application=PKW
)
This represents a major fraction of the battery's capacity. Note also that
at -20 F, the battery's capacity is much reduced from 68 F. As a guess,
I'd say it's reduced by 50%. That would make the block heater load between
42% to 64% of the available capacity; not much left over for starting.
In addition, since automotive batteries don't take discharging this much
too well (rather poorly, as a matter of fact -- 10 or 12 full capacity
discharges will kill an automotive battery), you'll want to use a marine
or deep cycle battery, which have less cranking capability.
Craig
