12vdc Device to 110vac Wall Power how-to?

[WARNING]I'm a total electrical newbie.[/WARNING]
So I have this 90 watt 12v dc heater (see image) and I want to plug it into a 110v ac wall outlet. I've never done this before; what do I need?
An internet search turned up "inverters" & "converters" (which do I need?) in the $60 range and even "universal (laptop) power supplies" [aka: "adapters" - great, yet another conversion category! LOL] in the $10-$12 range. Is it possible that I could get away with using a cheap laptop power supply?
I'm intimidated & overwhelmed. Thanks in advance.

I'm also not an electrician! Feel free to wait for another poster to back up what I am saying.

You need an AC to DC adapter, so yes, just like a laptop charger. However, the important part will be to use one that is rated for the amperage that this heating unit will pull.

As:
Watts = Volts x Amps
Amps = Watts/Volts


Amps = 90W/12V
=7.5 Amps

You will need an adapter that is rated for at least 7.5 amps

You will have to make sure your wire connections are sound, and it may be wise to wire a fuse into the circuit. You can get an "inline fuse holder" for this. They are inexpensive, as are the fuses.

Is this heater used for car seats?

Test it out extensively before putting it anywhere that could be dangerous!

Thanks for your reply John. :-)

That's okay! As long as you know the voltage (12V) and the watts (90W) you can work out the amps - which is 7.5 in this case.

This is a job for Ohm's Law.

P=VI (Power = Voltage * Current)

We know the power is 90W and that it operates at 12V, so we solve for I to see how much current it draws:

I=P/V = 90/12 = 7.5 amps

Now we should figure out what sort of resistance that heater presents as a load to the curcuit:

R=V/I (Resistance = Voltage / Current)

R = 12/7.5 = 1.6 ohms . . . this is almost a short circuit

A typical laptop power supply provides 18-22V at around 3-5A. It wants to see a load in the range of 4-6 ohms. Less resistance will mean that the load is asking for more current than the PSU can really deliver, and in trying it will heat up and probably die. The preferred failure would involve a fuse blowing in the unit, but there could be a light show and even sparky-burny type shenanigans.

Look for a power supply that is rated for the load you're attaching, ideally with built-in safety measures (and a UL logo on the outside). A decent sized 12V battery charger might work.

another route which i think of in my head. It might not be a smart idea. or it might be.


What i imagine you being able to do is to hook up that heater to a 12v car battery. Buy yourself a Junior battery tender or some type of battery charger, hook up the battery tender/charger to your battery and charge the battery as needed. The battery tender is small. Battery tender search

How long are you needing to use the heater for? You could probably hook a switch into the line to turn the heater on and off.
This depend on whether you need to run the heater 24/7 or if you need to run it for a few hours and than can charge the car battery.
I do not think the battery tender would work 24/7

I believe that if you use an adapter/power supply that is rated for a higher current/amperage than the 7.5A of the heater, let's say 10A, the heater will still only draw 7.5A and the adapter will have some space in reserve. Building such a cushion in is likely the way to go for safety.

So, in theory this KFD 12V 7.5A 90W AC DC Adapter Charger would work? Or is 7.5A too close for comfort?
What am I looking for as far as fuses? Can anyone point me to those?
Thanks again. This is a huge help. :-)

Mike, that PSU rated for the full load would be right at the ragged edge of its capacity and would probably die an early death. The advice from John is worthwhile...get something with some headroom.

Yeah, things get hot when run near their limit.
 Like mentioned a battery charger can usually handle 8 amps with some to spare.
They are common and some are very efficient.
You'd probably need a small battery too.
I don't think a battery tender puts out enough amps.

Mike Kenzie wrote:So, in theory this KFD 12V 7.5A 90W AC DC Adapter Charger would work? Or is 7.5A too close for comfort?
What am I looking for as far as fuses? Can anyone point me to those?
Thanks again. This is a huge help. :-)

Maybe search for one that runs at 120W?

Like this one:

https://www.amazon.com/JOVNO-100-240V-Converter-Transformer-5-5x2-5mm/dp/B08762MCLQ/ref=sr_1_2_sspa?dchild=1&keywords=12v+120W+power+adapter&qid=1613999677&sr=8-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFXT1VCTE9KN1dTRFYmZW5jcnlwdGVkSWQ9QTEwMzgyNDdPRDlVMVpNSlMzVEImZW5jcnlwdGVkQWRJZD1BMDY3NTIxODM3QlpDS01FQk1BQiZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=


Someone mentioned finding one with UL listing, that may be worthwhile, hard to say...


As for the fuses, you could skip this step, but I am talking about something like this:

https://www.amazon.com/MGI-SpeedWare-Inline-Harness-Automotive/dp/B07JQX3C8C/ref=sr_1_2_sspa?dchild=1&keywords=inline+fuse+holder+15+amp&qid=1613999854&sr=8-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExUTZXVlhWRlZTMTNVJmVuY3J5cHRlZElkPUEwOTUxNDE3MlQ5Q0Y0NERFUjFUVSZlbmNyeXB0ZWRBZElkPUEwMTQwMzU3SFNDQkJFQk9FRlRKJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

I think the most economic option would be to get a heater for 110V AC. It just a resistor, nothing fancy or valuable.
Any conversion device contains a bunch of non-trivial electronics, especially if it has to provide 8A.

So even if you already own the 12V heater, buying a 110V one will be the less expensive option.

Unless you need a 100W 12V supply anyway…

Sebastian nailed it. You would be better off getting a 90 watt 120volt ac heater. Anything from 2 60 watt incandescent light bulbs to an infrared one like this
https://www.amazon.com/BOEESPAT-Ceramic-Emitter-Reptile-Aquarium/dp/B088D2RYD2/ref=mp_s_a_1_5?dchild=1&keywords=light+bulb+heater&qid=1614197398&sr=8-5#

You would want a good bulb holder and a cage of some sort

Just use this, https://www.amazon.ca/ALITOVE-Transformer-Switching-Converter-Security/dp/B07DN7LPRH

Make sure you only use 1 heater per power supply because the dc heater is rated for 7.5 amps., and this psu is rated at 10amps.

Mike Kenzie wrote:[WARNING]I'm a total electrical newbie.[/WARNING]
So I have this 90 watt 12v dc heater (see image) and I want to plug it into a 110v ac wall outlet. I've never done this before; what do I need?
An internet search turned up "inverters" & "converters" (which do I need?) in the $60 range and even "universal (laptop) power supplies" [aka: "adapters" - great, yet another conversion category! LOL] in the $10-$12 range. Is it possible that I could get away with using a cheap laptop power supply?
I'm intimidated & overwhelmed. Thanks in advance.

Also if you want to use a laptop power supply as long as it is rated for 12vdc and over 90w OUTPUT!! then all you would need is a female dc coxial plug https://www.primecables.ca/p-358026-cab-6881-primecables-dc-power-pigtail-female-plug?from_pla=google&sku=366761#sku366761 provided the laptop charger has a male coxial plug like this:

You can also use this along with the psu to have the heater turn on and off based on the set temperature parameters. So let's say you want the heater to turn on at 80degrees F but turn it off at 85 degrees, you can set the probe in the soil let's say you are trying to heat a tray of seeds to germinate, then the temperature will always be between 80 and 85 degrees based on the reading of the probe and the ability for that heater to work against cold ambient temperatures. It's pretty simple, does that make sense? If not it is ok, this stuff confused me as well until someone explained it to me.

https://www.amazon.ca/Temperature-Thermostat-Controller-50-110%C2%B0C-Waterproof/dp/B07XXLDV5C/ref=sr_1_1_sspa?dchild=1&keywords=temperature+sensing+speed+controller+12v+dc&qid=1614217024&sr=8-1-spons&psc=1&smid=A28ZWXW3ZSVNZU&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFUM1pDMElLS1IwSVAmZW5jcnlwdGVkSWQ9QTEwNDA3MjgyR0NDMFZJRktIVTIwJmVuY3J5cHRlZEFkSWQ9QTA2ODIxOTVLTDZPQkxKRjc4R0Imd2lkZ2V0TmFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

C'mon Steve, tread lightly. We grow and improve through the patience of our mentors.

Douglas Alpenstock wrote:C'mon Steve, tread lightly. We grow and improve through the patience of our mentors.

Sorry bud, just a mild roast, if your Canadian and you don't roast the people you call friends, your Canadianing the wrong way. Also, I missed the full moon ceremony this month, eh!

Thanks for your help everyone.
I only need to run the heater for a few hours, maybe 3-ish hours max and I will be present monitoring it the whole time. Definitely not running it 24/7.
So on the battery tender idea, I do ACTUALLY have one of those (see attached images)! YAY! So, before I go buy something new, will this one that I already have work?
[COMMENCE POSSIBLY DANGEROUS NEWBIE QUESTION] The heating device's wires are not color coded nor stripe coded. How do I know the polarity? Does it matter? Would I just hook those alligator clips on the battery tender up to the exposed wires on the heating device? [/END POSSIBLY DANGEROUS N00B QUESTION]
Thanks again in advance.

Yes, you will need one of these though. You can't just hook up the wires to the charging clamps.

https://www.amazon.ca/Camecho-12V-Cigarette-Power-Electric/dp/B073ZBNP7K/ref=sr_1_12?dchild=1&gclid=Cj0KCQiA4feBBhC9ARIsABp_nbUlFDum80OXHwdQ7fwlZXA3l4aS74qz_QIdh

polarity doesn't matter

I don't think that battery could supply that much juice for 3 hours by itself. You will need to plug a charger into it.

Douglas Alpenstock wrote:I don't think that battery could supply that much juice for 3 hours by itself. You will need to plug a charger into it.

It is a charger as long as it is plugged into a 120vac outlet it will supply the 12vdc the heater needs. There is no info on the rated current output of the 12vdc accessory plug on it, so we have no way of knowing if it can supply the 7.5 amps to run the heater. I looked at the manual and there is no info, there is no info on any of the pictures I can see. It should work if the charger is plugged into 120v while the heater is in use. Using an adapter rated for 10amps would be enough to protect the heater side of the circuit, as for the device itself, the outlet is probably rated for 5-10amps. Worst case scenario the 12vdc accessory port should be fused internally and the heater blows the fuse.

Steve Harvey wrote:Yes, you will need one of these though. You can't just hook up the wires to the charging clamps.

https://www.amazon.ca/Camecho-12V-Cigarette-Power-Electric/dp/B073ZBNP7K/ref=sr_1_12?dchild=1&gclid=Cj0KCQiA4feBBhC9ARIsABp_nbUlFDum80OXHwdQ7fwlZXA3l4aS74qz_QIdh

Edited/deleted - posted in haste without really thinking about the battery booster pack.  

John Rosseau wrote:

Steve Harvey wrote:Yes, you will need one of these though. You can't just hook up the wires to the charging clamps.

https://www.amazon.ca/Camecho-12V-Cigarette-Power-Electric/dp/B073ZBNP7K/ref=sr_1_12?dchild=1&gclid=Cj0KCQiA4feBBhC9ARIsABp_nbUlFDum80OXHwdQ7fwlZXA3l4aS74qz_QIdh

Why is that?

I'm thinking that he should be able to attach the heater to clamps on the jump start unit. You're right that polarity shouldn't matter, and Douglas has a good point that it the jump starter may need to be plugged into the A/C outlet to keep it charged up while the heater runs.

Won't the heater just take the 7.5 amps from the jump starter, even though the jump starter can provide up to 600 amps?

Because it is dangerous and a fire hazard, which is why I would never recommend anyone do this.

Phew! Time-out, please.

Connecting to the charging clamps means you are connecting directly to the battery. No protection against short circuits. No protection against destroying the battery.

The charging clamps, connected directly to the (tiny) battery, provide a high-amperage boost up to 600 amps for 3-5 seconds maximum. Just barely enough to turn over an engine and start it. That's it.

Pulling power through the "cigarette lighter" outlet is good advice. There will probably be a 10-amp fuse in that circuit. You can buy a 10A fuse and fuse holder and connect it to the charging clamps if you want, achieving the same effect. It kills the power flow if there is too much current draw, or a short circuit. This reduces the fire hazard and protects your battery from instant destruction.

The other question is the amount of power you will be drawing over a 3-hour period. The battery is tiny -- it fits in the palm of your hand. Think of it as a bucket that can be emptied quickly but refilled slowly. The charger it came with is probably designed to fill slowly. The heater you're connecting is designed to empty quickly. If these things don't more-or-less even out, the battery may discharge to the point where permanent damage occurs.

Hope this helps a little.

Using the clamps is still going to be a fire hazard regardless of fusing, if the clamps touch each other they are going to arc and cause sparks. If OP was away from the heater and this happened, let's say a cat decides to play with the clamps, this is not good. I would sell this jumpstarter on marketplace or something they are useless and just buy the appropriate 10amp 120vac to 12vdc Power supply off amazon for $20 with free shipping, sell the jumpstarter for $20.

PSU from USA Amazon. The red and black wires are where your heater would go, and the other three are your ac120v from a wall plug, you would have to get a power cord from an old device you might have.



https://www.amazon.com/Switching-Universal-Regulated-Security-Computer/dp/B082TN889J/ref=pd_sbs_3?pd_rd_w=x2OMd&pf_rd_p=527ea27c-adf6-4b67-9c5f-265eb29e0622&pf_rd_r=2KHCNSVRYJPVG7A818TR&pd_rd_r=e649006a-0453-4ae0-b436-2b8431fbb812&pd_rd_wg=t41Yb&pd_rd_i=B082TN889J&th=1