Hybrid Car – More Fun with Less Gas

flooring heating question

register ::  Login Password  :: Lost Password?
Posted by 1234 on July 20, 2004, 4:56 pm
I have one of those 300 watt @ 110 volt floor heaters in my bathroom.
what kind of amps would it draw if I put (solar) dc directly into it or
would that be a bad idea. I am just thinking it would be more efficient
than converting my dc to ac first

Posted by Kent Hoult on July 20, 2004, 6:03 pm
If it's just a resistance heater, then 300W / 110VDC = 2.7 Amps. So you will
to put enough 2.7 Amp panels in series to get to this voltage and amperage.
Of couse you
then only get floor heat when the sun shines....

If you feed it a lower voltage, you won't get nearly as much heat. If you
up-convert DC
battery voltages to get up to 110, then you DC-DC converter losses are
probably not much
different than your inverter losses would be.

If there are any electronics involved in this heater (other than a simple
bi-metal thermostat), then you
should probably stick with the AC unless you want to redesign/replace the


PS: I'm sure there's another crew on this newsgroup that will point out that
it's much more efficient
to skip electric conversion altogether, and use a solar hot water panel to
run hot water under your floor.

Posted by Dave Hinz on July 20, 2004, 6:49 pm
Actually, if you do your DC/AC conversion in the same space you're
trying to heat, the inefficiency of the conversion process turns into
heat anyway.

Posted by James Baber on July 20, 2004, 6:52 pm

1234 wrote:

It would work, and it would be more efficient, but it is still a bad idea.

You would need to arrange your panels in series (I am assuming you plan to use
five (10) of the common 120W @ 24 VDC panels wired in series) to get an
approximate 120 VDC output @ 5 Amps, similar in voltage to what the floor
heaters require.  NOTE: this also gives you a total of 600 Watts (so you would
need 2 heaters to absorb your output)

  Next, if you want any heat at any time other than the 4-8 hours midday when
you will produce PV power, you will have to store the output of the panels in a
set of batteries. You could arrange a set of (10) 12 VDC batteries in series to
do this, but you still need a charge controller to correctly maintain the set of
batteries Oh, by the way you will need to add another PV panel to account for
your systems additional voltage needed to charge the 12 VDC batteries (they need
13+ VDC to charge) By the way don't use car batteries, they will quickly fail,
you need deep cycle batteries like RV batteries.

Two other problem areas, that are related to each other.  Circuit protection
devices, circuit breakers or fuses, for a 120 VDC circuit must be rated for
600VAC / 120VDC.  The same 600VAC / 120VDC ratings are also required on any
switches in your system, which means that you can't use the original heater
switches, since I am sure they don't have this large of an rating. These
problems occur because AC circuits are self quenching for the arc created when a
loaded circuit is interrupted, but the DC arcs are only quenched by larger
distances. (the cyclic reversal of current flow puts the arc out)

    I am sorry to be a wet blanket on such a neat sounding idea.
to avoid having to make supply
Jim Baber


1350 W Mesa Ave.
Fresno CA, 93711
(559) 435-9068
(559) 905-2204 cell

Email jim@NOJUNKbaber.org

Posted by 1234 on July 22, 2004, 6:54 pm
 Conclusion....some good responses to my question but I now conclude this
planet is doomed.
By the way the floor heating is a simple resistance wire yes it has a t
stat and would have been easy to bypass and go DC I in stalled it my
self during a bathroom reno.
Any way I bought one of those 45 watt 3 amp soler kits complete with
charge control from Canadian Tire for 500.00 After playing with it for
three sunny days I conclude that all I got here is a 500.00 doller
trickle charger for my battery to start my GAS powered generator lol
....Home solar is a joke and a total waste of money. I figured it would
at least run my coleman 12v 2 amp cooler. At peak sunshine the voltage
peaks @ 10.5 v with the cooler on and drops to about 5 0r 6 when slight
clouds roll over.
So in order to run the cooler during the day and replenish my batteries
in my camper from last nights use I would need about 15 hundred dollers
of solar panels what a waste. Shit should have got that honda generator.
Probably looking at ten grand for enough panels to heat the floor in my
house forget that idea lol. Oh well when I go camping I will set the dam
thing up anyways and lie that the sun is cooling my beer.
1234 wrote:

This Thread
Bookmark this thread:
  • Subject
  • Author
  • Date
please rate this thread