hoola Posted April 4, 2015 Share Posted April 4, 2015 I am wanting to install a battery assisted solar array that provides a dc line to small (500 watts or so) passive resistance space heaters throughout the house. Since 120 vac converts to 84.84v RMS, wouldn't that be the voltage in DC to deliver an equivalent heating effect? Link to comment Share on other sites More sharing options...
Acme Posted April 4, 2015 Share Posted April 4, 2015 Are you asking if you can run an AC heater on DC? Anyway, the usual method is to use an inverter to change you DC 12V battery output to AC. From there it's a matter of wattage for both the heater and the inverter output. My experience is that the inverter has to exceed the load in its wattage because the initial surge will trip the inverter safety control. For example, my 800watt inverter won't run my 750watt heater. Link to comment Share on other sites More sharing options...
hoola Posted April 4, 2015 Author Share Posted April 4, 2015 I am going to series 24 volt solar cells to get the needed voltage, charging series wired 12v batteries to match. So the intended voltage will be higher that the standard 12v system...this will eliminate the inverter... Link to comment Share on other sites More sharing options...
EdEarl Posted April 4, 2015 Share Posted April 4, 2015 A pure resistor (heating element) will run on the either AC or DC of the same wattage. Measure the resistance with a meter and use Ohms law to determine volts needed for rated power. On the other hand, the fan will not run on DC. Since the motor and resistance element are wired in parallel, you will need to disconnect the motor for DC operation. 1 Link to comment Share on other sites More sharing options...
Acme Posted April 4, 2015 Share Posted April 4, 2015 I am going to series 24 volt solar cells to get the needed voltage, charging series wired 12v batteries to match. So the intended voltage will be higher that the standard 12v system...this will eliminate the inverter...I don't think you can eliminate the inverter. Certainly not if the heater has a fan. Sounds to me like you're inviting trouble by jury-rigging a setup for which there is already standard equipment. Link to comment Share on other sites More sharing options...
hoola Posted April 4, 2015 Author Share Posted April 4, 2015 the real question is....will 120 vac give the same energy to a fixed resistor that 84.84 vdc will give it? Link to comment Share on other sites More sharing options...
Acme Posted April 4, 2015 Share Posted April 4, 2015 A pure resistor (heating element) will run on the either AC or DC of the same wattage. Measure the resistance with a meter and use Ohms law to determine volts needed for rated power. On the other hand, the fan will not run on DC. Since the motor and resistance element are wired in parallel, you will need to disconnect the motor for DC operation.There may also be an issue with the thermostat. Link to comment Share on other sites More sharing options...
hoola Posted April 4, 2015 Author Share Posted April 4, 2015 (edited) I have no problem with disconnecting the heat element for dc, and run the fan, thermostat and pilot light on regular AC. A added relay will isolate the two systems, as the thermostat kicks on the fan, it will activate the relay which engages the DC to the heat element. My question is an energy equivalency question for the heat element, so as not to over-current the element, which I think I would do if I used 120vdc to it... By having the thermostat not having to carry the heavy load of the heat element, and only a small fan and low current relay, this will save wear and tear on that component (often arc damaged) and shift the burden of heat off the grid and onto the solar/battery array... Edited April 4, 2015 by hoola Link to comment Share on other sites More sharing options...
Acme Posted April 4, 2015 Share Posted April 4, 2015 I have no problem with disconnecting the heat element for dc, and run the fan, thermostat and pilot light on regular AC. A added relay will isolate the two systems, as the thermostat kicks on the fan, it will activate the relay which engages the DC to the heat element. My question is an energy equivalency question for the heat element, so as not to over-current the element, which I think I would do if I used 120vdc to it... By having the thermostat not having to carry the heavy load of the heat element, and only a small fan and low current relay, this will save wear and tear on that component (often arc damaged) and shift the burden of heat off the grid and onto the solar/battery array... Pilot light? Link to comment Share on other sites More sharing options...
hoola Posted April 4, 2015 Author Share Posted April 4, 2015 oh yeah, I forgot the 20ma pilot light ! Link to comment Share on other sites More sharing options...
Acme Posted April 4, 2015 Share Posted April 4, 2015 oh yeah, I forgot the 20ma pilot light !On a resistance heater? I don't think so. Link to comment Share on other sites More sharing options...
hoola Posted April 4, 2015 Author Share Posted April 4, 2015 I volunteer at a recycle center and am in charge of the electrical / electronics that comes in. I check over the stuff that comes in and can have almost anything I want, including flat screen tvs, stereos and computer stuff...we also get in tons (literally) of lead acid batteries and I have checked out and have accumulated 40 good ones, so my storage expenses are almost nothing...hence the plan to have the heaters ready for next winter.... well, acme, I never actually measured the current of a neon mini lamp....a rather insignificant value, I am sure..... anyone in here collect vintage/early Apple stuff? I have been sitting some back rather that see it go to the crusher... Link to comment Share on other sites More sharing options...
Acme Posted April 4, 2015 Share Posted April 4, 2015 I volunteer at a recycle center and am in charge of the electrical / electronics that comes in. I check over the stuff that comes in and can have almost anything I want, including flat screen tvs, stereos and computer stuff...we also get in tons (literally) of lead acid batteries and I have checked out and have accumulated 40 good ones, so my storage expenses are almost nothing...hence the plan to have the heaters ready for next winter.... well, acme, I never actually measured the current of a neon mini lamp....a rather insignificant value, I am sure..... anyone in here collect vintage/early Apple stuff? I have been sitting some back rather that see it go to the crusher... An indicator light is not a 'pilot-light'. You are gonna seriously harm yourself or others and property. I'm done here. Link to comment Share on other sites More sharing options...
hoola Posted April 4, 2015 Author Share Posted April 4, 2015 (edited) any serious responses to my energy equivalence question would be appreciated...otherwise don't respond.... I suppose the practical method of simply hooking up a 100watt light bulb to 120 vac, then subbing in 120 vdc and comparing the resultant luminosity could offer a way of determining the power relation between AC and DC...this relationship should transfer over to a heat element...thanks for all the good help guys ! Edited April 4, 2015 by hoola Link to comment Share on other sites More sharing options...
John Cuthber Posted April 4, 2015 Share Posted April 4, 2015 An indicator light is not a 'pilot-light'. You are gonna seriously harm yourself or others and property. I'm done here. Others disagree. http://www.globalspec.com/industrial-directory/120v_neon_pilot_lights it's pretty much a no-go if it's a fan heater. The normal thermostat will be designed to switch AC and may not cope with a DC source. If you can rewire it so that a suitably rated relay switches the main current, there should be no problem. Link to comment Share on other sites More sharing options...
studiot Posted April 4, 2015 Share Posted April 4, 2015 (edited) +1, acme. Don't fiddle with the mains unless you can be certain you know what you are doing, including the possibility of invalidating any household insurance you have. Edited April 4, 2015 by studiot Link to comment Share on other sites More sharing options...
Danijel Gorupec Posted April 4, 2015 Share Posted April 4, 2015 the real question is....will 120 vac give the same energy to a fixed resistor that 84.84 vdc will give it? A resistor connected to 120VAC will give you the same output power as the same resistor connected to 120VDC. This is how 120VAC is defined... The 120VAC has amplitude of about 170V. Link to comment Share on other sites More sharing options...
studiot Posted April 4, 2015 Share Posted April 4, 2015 There are also potential building control issues. Electrical rules in the US are stronger than in the UK. In particular the standard domestic supply for A/C, heating and other large power users is to use 240 volts. The 120 is only half of the split phase system and designed for lower power/duration equipment. In the US the neutral is the centre of the split phase system and must be grounded. It is ironic that in the UK it is illegal for the consumer to ground the neutral, in the US is is illegal for him not to. Link to comment Share on other sites More sharing options...
hoola Posted April 4, 2015 Author Share Posted April 4, 2015 thank you danijel, that is the answer I was seeking... Link to comment Share on other sites More sharing options...
encidentt Posted May 15, 2015 Share Posted May 15, 2015 hey hoola whats up with that apple merchandise? Link to comment Share on other sites More sharing options...
Phi for All Posted May 15, 2015 Share Posted May 15, 2015 hey hoola whats up with that apple merchandise? ! Moderator Note Hoola will be opening another thread to discuss this so it doesn't interfere with the discussion about converting a space heater. Please don't bring up this merchandise here. Link to comment Share on other sites More sharing options...
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