Does anyone power their engine block heater with portable power?

Discussion in 'Gen 2 Prius Technical Discussion' started by JamesWyatt, Sep 2, 2008.

  1. JamesWyatt

    JamesWyatt Señior Member

    Jul 9, 2008
    Allen, TX
    2007 Prius
    ...for heating your engine block while away from home. Is there enough juice in them to run the engine block heater for the time required... 2 hours was it?

    Reason I'm asking is, if so, why not use a portable power supply (portable jump starters with outlets) mounted in the trunk area? (Mounted so it could be easily removed of course.) You could run an extension cord from the engine block heater plug back through the cabin to the portable supply, putting a timer inline for easy access... provided we have a nice little firewall hole, of course. When discharged, just remove the portable unit and recharge.

    I was picturing going out to the car two hours before leaving work and setting the timer. :nerd:

    I couldn't find a thread that talked about this exactly, so forgive me if I have rehashed. *run, duck, cover* :D
  2. JimboK

    JimboK One owner, low mileage

    May 1, 2006
    Chesterfield, VA
    2005 Prius
    The consensus seems to be that three hours is optimal, but no matter. Two would still benefit.

    I've thought through a somewhat similar approach after buying a townhouse last year with no easy way to plug in. My idea was to use a battery and inverter to power it at home, and move the power supply inside for charging while I was gone. I concluded this was too expensive and impractical.

    Here is the analysis I used, modified slightly to fit your circumstances: Let's assume a 12V battery for the jump starter, 2 hours charge time, and a 400W heater. Let's also assume a complete discharge of the jump starter. You wouldn't want to do that for the sake of longevity, but it makes the math simpler. The math suggests a need for 67 amp-hours at an absolute minimum: 400(W) ÷ 12(V) * 2(hours). Most (all?) jump starters have much lower amp-hour ratings, and their lead-acid batteries likely won't survive long with daily deep cycling. Of course, a less-than-complete discharge would require an even higher amp-hour rating.

    Now, I'm not the most educated on things technical, so my analysis is subject to correction.
  3. qbee42

    qbee42 My other car is a boat

    Mar 2, 2006
    Northern Michigan
    2006 Prius
    Jimbo, I think your conclusion is correct. In this case it is more economical to use the Prius engine as an engine preheater, or in other words, just get in and drive.