How to generate 100 watts of heat from a car battery

[John1397]

I have lots of batteries 12 volt charged by the sun what I need is something that would draw 100 watts and give heat when connected to a car battery? I have ac heating pads, 2000 watt hot water elements lots of copper wire, light bulbs any other ideas?

 

[russ_watters]

Connect any device that uses 100 Watts to the car battery. The easiest I can think of is a 100 Watt light bulb (connected via an inverter, of course). But you already seem to know this, so I'm not sure what you are really asking...

 

[lewando]

This would do the trick-- a Vishay RH1001R400HJ01.
Be very careful. That is, use this part in a manner consistent with the manufacturer's heat sink requirements.

Please say more about your application.

 

[Nik_2213]

One tweak: Is the car battery being charged or providing power to anything else ? The ~ 8 amps you're drawing is based on a *nominal* 12 V battery voltage .

Hmm: Winter ? DIY cabin heater ?? You MUST have appropriate wiring, connections, insulation, line-fuse and switch. A safely mounted heat-sink, given a central power-resistor will be much hotter than the fin tips. Thermal transfer paste. A cooling fan ? Two such ??
Please consider getting a well-rated, low-voltage cut-off such as the KEMO series, as used to protect eg RV & SUV batteries against deep-discharge...
As ever, 'Due Care, Please' ??

Um, you may do better to have several power resistors, distributing the heat across the heat-sink. Just so their network appears as 1R4 ( 1.4 Ohms) load...
FWIW, if you have eg a pair of 2R8 ( 2.8 Ohm) in parallel, they may be individually switched to allow 'Full' or 'Half' power...

{ V = I x R, I = V/R, Power = I x V = V x V / R. Here, 100 = 12 x 12 / R, so R = 1R4 ( 1.4 Ohms) to first approximation per #L above ... }

 

[Asymptotic]

Work it out.

1. Amps=Watts/Volts. 100W/12V = 8.3 amps. (you'll need to know current to determine required wire size).
2. Resistance = Volts/Amps. 12V/8.3 amps = 1.4 ohms.

You could hook up one of those 2000W water heater elements, but probably wouldn't be impressed with the results. Work it backwards from heater specifications ...
2000W/240V is a typical water heater rating. How many ohms is that?
Watts=Volts * Amps, and Ohms=Volts/Amps. A bit of algebra yields the formula Ohms = Volts²/Watts.
240²/2000W = 28.8 ohms.

How much current flows through 28.8 ohms when 12 volts is connected across it?
Amps=Volts/Ohms. 12 volts/28.8 ohms = 0.42 amps.
How much power is this? 0.42 amps * 12V = 5 watts.

Just because the heater is rated for 2000W doesn't mean that's how much power it'll provide - that's only true when supplied with 240V.If you have a bushel basket full of water heater elements you could connect 20 of them in parallel across a 12 volt source. Each one will contribute 5 watts; 5*20 = 100 watts.

@lewando spec'd a 1.3 ohm Vishay resistor (it's probably the closest standard resistance to the calculated 1.4 ohms), and that'll do the job. I'll second his inquiry, too - what is you application?

 

[John1397]

I was wondering if one used an AC baseboard heater rated 1000 watts at 120 ac then hook it to 12 volt dc how would this work you then have ten times less voltage would you have ten times less watts? Light bulb would maybe work except I want to generate heat not light.

 

[lewando]

Analyze the AC baseboard idea using P = V²/R.
1000 = 120²/R. R = 14.4 Ω, the resistance of the AC baseboard heater.
P_12V = 12²/14.4 = 10 W.

Also, incandescent light bulbs do a much better job of generating heat than light.

 

[Nik_2213]

Snag with using 120 V-rated heaters on 12 Volts is their cold resistance may be a lot less than you expect, but more than you want. Given their non-linear thermal characteristics, they'd need some experimentation. Same applies to 120 V or 220 V incandescent lamps...

FWIW, 'rough service' lamps are less efficient than the 'regular' types, so better for turning current into heat rather than light...

 

[russ_watters]

Also, incandescent light bulbs do a much better job of generating heat than light.

And all of the light becomes heat once absorbed.

 

[John1397]

Analyze the AC baseboard idea using P = V²/R.
1000 = 120²/R. R = 14.4 Ω, the resistance of the AC baseboard heater.
P_12V = 12²/14.4 = 10 W.

Also, incandescent light bulbs do a much better job of generating heat than light.

I got to try that do not know if 10 watt is going to be much heat.

 

[Averagesupernova]

Buy some cheap sealed beam automotive headlamps. Get some that have two filaments each. You should be able to combine them up in such a way to get close to your target wattage.

 

[lewando]

...do not know if 10 watt is going to be much heat.

I do not know either. Even 100 W may not deliver much heat, depending on what you are trying to do. Heating up an ice fishing cabin? Probably not.

 

[Asymptotic]

Analyze the AC baseboard idea using P = V²/R.
1000 = 120²/R. R = 14.4 Ω, the resistance of the AC baseboard heater.
P_12V = 12²/14.4 = 10 W.

Also, incandescent light bulbs do a much better job of generating heat than light.

Brings back Christmas memories of my sister and her Easy-Bake oven ... it used (2) 100 watt light bulbs as heating elements.

 

[Asymptotic]

I got to try that do not know if 10 watt is going to be much heat.

What are you attempting to accomplish?

5 watts can seem to be far too much heat - ask anyone who had accidentally bumped up against a fully loaded 5 watt 'sand' resistor while troubleshooting a circuit board, and toasted a part of their anatomy in the process. That same 5 watts spread out over increasingly larger areas becomes decreasingly less noticeable.

 

[OmCheeto]

Buy some cheap sealed beam automotive headlamps. Get some that have two filaments each. You should be able to combine them up in such a way to get close to your target wattage.

This works. I just happened to have two sitting in my living room, and they each draw 5 amps @ 12.4 vdc = 62 watts/lamp

per Wikipedia; "The 9004 is rated for 65 watts (high beam) and 45 watts (low beam) at 12.8 volts."

so I'm guessing the low beam element failed on them.

 

[John1397]

Only downside with auto headlamps is only have 300 hour life span. I have batteries and solar panels and to much power left over so I was trying to find a cheap way of using the power up.

 

[256bits]

There are plug in 12 v gadgets that can suit your fancy,
Thermoelectric coolers, add on windshield defrosters with a blower are just 2 examples.
Go visit the automotive section of the store and see what other creatures lurk there.

 

[OmCheeto]

Only downside with auto headlamps is only have 300 hour life span. I have batteries and solar panels and to much power left over so I was trying to find a cheap way of using the power up.

Wow. Seems like a waste. I would just disconnect the excess solar panels and put them into storage. They last longer that way. [ref]

If you're not willing to do that, just wire 4 bulbs in series and parallel. I found https://www.4wheelparts.com/Lighting-Lighting-Accessories/Hella-HB1-9004-Halogen-Bulb-Clear-9004.aspx?t_c=14&t_s=67&t_pt=4730&t_pn=HLA9004, brand new.
I have a feeling they would last longer than you will live.

There are plug in 12 v gadgets that can suit your fancy,
Thermoelectric coolers, add on windshield defrosters with a blower are just 2 examples.
Go visit the automotive section of the store and see what other creatures lurk there.

That's just too easy!

120 watt, 12 volt thingy. $9.99

ps. I was right in the middle of doing Boltzmann calculations when you posted that.

Temperature of a halogen bulb: 5300°F (filament made of Tungsten)
Melting point of tungsten: 6200°F
Temperature of 4 halogen bulbs wired in series-parallel: 3600°F​

 

[Cameron Nicoll]

Hi, I'm not an engineer but I have a train load of solar experience. Can I ask why you think you need to use this extra power?
Do you have your panels directly connected to your batteries or are you using a regulator?
If you're using a regulator, there is no need for anything else. The regulator will only deliver as much power as your load and batteries require.

 

[Nik_2213]

I tried to get a car 'screen defroster' in UK, discovered reputable suppliers had 'pulled' all of them off their shelves.

Bunch of issues across the several brands...
Not fused. (!)
No low-voltage cut-out, so could flatten battery when you needed it most.
No thermal cut-out, so could 'Halt & Catch Fire' if air-flow compromised.
Shabby wiring, which could over-heat.
Fake CE markings; first, 'trial' shipment was genuine, subsequent stock were low-quality, look-alike 'clones'.

So, look for 'UL' approval tag in US, and 'Due Care, Please' !

 

[gary350]

I have lots of batteries 12 volt charged by the sun what I need is something that would draw 100 watts and give heat when connected to a car battery? I have ac heating pads, 2000 watt hot water elements lots of copper wire, light bulbs any other ideas?

This is an electronic question, not a physics question.

12 volt car battery is actually 13.2 volts. Amps x volts = watts.

100 watts/13.2 volts = 7.57amps. If you have a 500 amp battery/7.57 amps = it will run for 66 hours then battery will be dead.

Your geographical location determines how much power you get from solar.

Phoenix AZ has no clouds you get about 14 hrs per day in summer and 7 hrs in winter from solar.

Tennessee where there are lots of clouds you get 14 hrs of sun in summer but 50% clouds gives you 50% sun = 7 hrs per day. TN is over cast most of the winter you be lucky to get 10 minutes of solar per day in winter Dec to April.

Wind power may be a better choice of power to charge a battery it depends on your geographical location.

If you live in Phoenix you need 7.57 x 2 = 15.14 amps from solar to keep your battery charged if you use enough power to run it dead every day.

Use a 12 VDC inverter to 120 VAC from Harbor Freight to run your other items, heating pad, 2000 watt heating element, light bulb.

I have 135 watts of solar connected to a 100 watts of lights in the work shop, in winter lights never come on too many clouds. In summer lights goes ON and OFF with passing clouds all day. NO lights after dark I have no battery. To do my system right I need a storage battery. Solar is worthless around here but we have lots of wind. I have a wind generator that needs to be put up.

 

[John1397]

Hi, I'm not an engineer but I have a train load of solar experience. Can I ask why you think you need to use this extra power?
Do you have your panels directly connected to your batteries or are you using a regulator?
If you're using a regulator, there is no need for anything else. The regulator will only deliver as much power as your load and batteries require.

I just have so many batteries and so many solar cell panels and no 12 volt dc to 120 volt ac converters that just wanted to find a cheap way to use power up as heat. My system has 1kwh of extra energy that is not used when the sun shines all day.

 

[Cameron Nicoll]

I just have so many batteries and so many solar cell panels and no 12 volt dc to 120 volt ac converters that just wanted to find a cheap way to use power up as heat. My system has 1kwh of extra energy that is not used when the sun shines all day.

Oh ok. I don't think there is a cheap way to do it. You can get programmable charge controllers that can supply power to load once the batteries are charged but they are quite expensive. It would make an interesting Arduino project if you're into that kind of thing.
Otherwise it would be a manual system so you'd have to turn on the heater once you've made sure your batteries were full. I'm assuming of course that battery longevity is your main priority.

 

[Mark Harder]

FWIW, if you have eg a pair of 2R8 ( 2.8 Ohm) in parallel, they may be individually switched to allow 'Full' or 'Half' power...

A 2 ohm in parallel with a 5 ohm is about right resistance: 1.43 ohms. The total dissipation will be more like 100.5 W, so be careful handling them under power.
I found an eBay listing for $1.39 ea. with free shipping, from China. The particular supplier won't guarantee delivery before Mar. 12, so they might not be the best choice. But you should be able to find other suppliers.

 

[Questor2]

Getting spare heat in the winter would be useful, just one 40 watt incandescent light bulb keeps my well-house from freezing up in the winter (It is insulated), which is why I was very worried when they started switching away from selling the nice warm incandescents to Leds and mercury vapor. I can't keep my water pipes and tank from freezing with those. I could run a heat tape but it uses up a lot more electricity. I am old fashioned and hate how we all have to depend on electric, but it is handy. Otherwise I would be using an old fashioned well pump which I did have when I started out living with no electric in the country since you can't pump water from a 200 ft well with solar. At least not the kind poor folk can afford...But I really liked my hand pump and would almost be willing to go back to it .
I'd say find some use for the extra heat from the 4 auto headlights, I bet they give enough to heat a little cabin if you could put them in a box ...then you would have one of those room heaters that they advertised for like $250 as all the newest thing a couple years back and all they were was just a super fancy case with a heat light bulb inside.. maybe an auto headlight! (You would need to put them in a box because the light would be blinding.. from 4 headlights).

 

[Averagesupernova]

Getting spare heat in the winter would be useful, just one 40 watt incandescent light bulb keeps my well-house from freezing up in the winter (It is insulated), which is why I was very worried when they started switching away from selling the nice warm incandescents to Leds and mercury vapor. I can't keep my water pipes and tank from freezing with those.

I use something similar. I like the fact that I can see the light through a small crack and know it is working. A heat tape won't do that for you.

 

[Ketch22]

Just a side note, for your consideration.
I recently designed a convection oven for process curing of a composite material. The substrate was highly thermally sensitive. I found that 4 staged 100 watt incandescent bulbs worked very well as heat sources. I used a fan unit to normalize temperatures and staged the bulbs for a soft start and finish to the heat curve. I found the heat efficiency to be very good. Even more important The end customer was really impressed with how well this met his needs.
I would add that that the real important part is that the oven was well insulated so that the bulbs could maintain temperature with a moderate differential. This particular unit normally operates 52^oC- 55^oC above ambient. I am sure this oven will be in use until incandescent bulbs are no longer available.