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Russian Landy
| | Posted on Friday, December 06, 2002 - 10:17 am: | 
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Any electrical geniuses in this group? Here's the deal: it's going to be -22 degrees C (about 8 below F) every night the next week or so here in frigid Moscow, Russia, which means we're colder right now than Barrow, Alaska. Brrrrr!
I installed an Espar (Eberspaecher in Europe) fuel heater in my TDi Disco (1998 model, diesel) which is really dandy, because it lights off on a timer in the morning and the big diesel is toasty warm (both the engine and the interior) when I climb into her to drive to work.
The only problem is that although the heater burns diesel fuel from the tank, it also draws about 55 watts of electrical power (like one headlight), and my drive to work is only 10 minutes or so, so the battery starts to run down if I don't drive around a lot during the day.
I'm thinking about putting in a second battery with a Hellroarer splitter and run the heater off that. Meanwhile, I'm just letting the Disco idle for twenty or thirty minutes (it's a diesel so uses very little fuel doing that) in the evening before I go home while the Espar warms everything up. But I'm always worried about whether I'm keeping the battery charged or not.
Here's the question:
How much current does the alternator put out when the truck is idling at 700 RPM? Is it enough to run the Espar and maybe put a little charge on the battery? Does anyone know how RPM relates to alternator current? I think the alternator is rated for 100 amps which would be a pretty hefty 1200 watts, but is that only at high RPM?
Thanks for your advice and greetings from frosty Moscow! |
Paul T. Schram (Paulschram)
| | Posted on Friday, December 06, 2002 - 10:32 am: |
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Typically, alternator output is fairly low at idle and most don't begin to generate much voltage or current until they reach somewhere around 1200 RPM.
your suggestion of a secondary battery is probably right on the money as far as a good alternative as everything else I could think of (mainly a coolant heater run off of house electricity) might not be suitable, not to mention, how many watts would you need to heat up an engine in ambient temps that low? Although, now thatI think of it, if you can get power to it, that might be a solution.
Stay warm!
Paul |
John Davies
| | Posted on Friday, December 06, 2002 - 11:28 am: |
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The real solution would be to kick the idle up above 1000 rpm while you are charging. Consider installing a hand throttle cable - they are available in universal form to fit most vehicles, or you could engineer your own. An aircraft vernier-adjustable, locking push-pull cable (throttle or propeller control) would work great, but expect to pay $$$$.
Adding a second battery will NOT solve your problem. You need to get those amps flowing back into the battery.
Also, do you know definitely that your alternator is working correctly? One blown set of diodes will seriously degrade charging output, and you won't have much luck recharging, even at a fast idle. Remove the alternator and get it bench tested if you have any doubts, or get an inductance type ammeter and test the charging current yourself.
Good luck, stay warm. |
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