GL1800Riders Forums banner
  • Hey everyone! Enter your ride HERE to be a part of MAY's Ride of the Month Challenge!

1 - 20 of 34 Posts

·
Registered
Joined
·
868 Posts
Discussion Starter · #1 ·
I need some help from those that understand OHM's Law a little better than I.

I know that E = IxR or in my case R = E divided by I

Now my problem. -- I found some heated panel on ebay and bought several and made a heated jacket. The Jacket worked quit well, except when leaning back against the back rest you feel that heat on your back more than the fron. What I need to do is install a resistor in the back panel to lower the heat some, but not all. Maybe by 25%.

The panel(s) is pulling 2.5 amps (actually 1.25, but have 2 panels). Voltage is 12V. Using OHM's Law, what size resistor should I install? If I take
12v(E) and divide it by the 2.5 amps (I), I get 4.8 ohms (R). But is that 4.8 ohms --- 480 ohms, 4800 ohms etc?

Since I want to only reduce the heat (engery) do I install a different resistence?

In other words, what do I need to do?

I'm using a Gerbing temp control, but still need to change the heat ratio front to rear.

Thanks,
 

·
Banned
Joined
·
4,623 Posts
The load is 4.8 ohms ... you could install a 4.8 ohm resistor in series, the resistor would dissipate half the power and the panels the other half.

The total power you are using now is 30 watts to the back panels.
If you install a 4.8 ohm resistor in series, you will now have 9.6 total ohms in the load or half the current times the voltage .. 1.25 amps times 12 = 15 watts, half in the panels and the other half in the resistor, The resistor should be rated for at least 10 watts, but I like to double the wattage ratings for long term use.

So, buy a 10 ohm 20 watt resistor. wire it in series and the back panels will be comfy and the resister fairly warm...

Good Luck !!
 

·
Registered
Joined
·
747 Posts
im a structural engineer and all i learned was:

angle of the dangle depends on the mass of the a__

AD=%MA
 

·
Registered
Joined
·
868 Posts
Discussion Starter · #4 ·
Tom,

Thanks for the info. It's been years since I tried to apply what little I know about electronics.

In other words, I don't understand everything I know about electronics :)

I'll get the resistor and get it installed tomorrow.

Terry
 

·
Registered
Joined
·
868 Posts
Discussion Starter · #5 ·
Barn,

I total agree with you analogy. At my age, my mass has declined to the point that the angle of my dangle is mostly downward :shock:
 

·
Registered
Joined
·
1,142 Posts
I would add that your voltage is probably closer to 13.5 than to 12....
But that shouldn't be terribly significant.


What are these anels you found... I'm interested in the same Idea...
 

·
Vendor
Joined
·
22,240 Posts
The problem you are going to have is not finding the proper resistance value, but getting the proper WATTAGE of the resistor, since it will have quite a bit of amperage passing through it. The resistor itself will also heat up significantly as well so keep this in mind when you locate it. Like Tom said, if you used a 4.8 ohm resistor it would dissipate about 8 watts of power, and if you round that up to 10 watts, and double it for safety, you would need a 20 watt resistor, which is fairly large. It also is wasting those unused watts, so it is not the most efficient approach.

An alternative method might be just to wire the panels in series with each other, as this would significantly reduce the current flow (cut it in half) and may achieve the results you are looking for, though it would lower the temp of BOTH panels.
 

·
Registered
Joined
·
4,246 Posts
KA7W said:
The total power you are using now is 30 watts to the back panels.
If you install a 4.8 ohm resistor in series, you will now have 9.6 total ohms in the load or half the current times the voltage .. 1.25 amps times 12 = 15 watts, half in the panels and the other half in the resistor, ...
So, according to your calculations his panels go from 30 watts to 7.5 watts (half of 15 watts, the resistor getting the other 7.5).

Going from 30 watts to 7.5 watts is much greater than his intended 25% reduction.

If he were to add a 1 ohm, 10 watt resistor in series with the panels he would be much closer to what he wanted.

The total resistance would then be 5.8 ohms, which (at 12 volts) would draw about 2.07 amps and provide about 24.8 total watts. The panels would have to dissipate about 83% of that (4.8 / 5.8, or about 20.5 watts) and the one ohm resistor about 17% (1 / 5.8, or about 4.2 watts). At 14 volts everything goes up a bit, but the ratios would stay the same. Using a 10 watt resistor provides a margin of safety, but you still need to find a good place with air circulation to mount it.

-Bob
 

·
Registered
Joined
·
638 Posts
The real answer is to not have any heated panels on the back of the garment that is in contact with the backrest. You're not losing heat through that area anyway.
I wired my jacket myself from a kit and those were the instructions. The wiring ran down the back from the neck to the shoulder blades but no further.
 

·
Registered
Joined
·
4,823 Posts
Ellary said:
The real answer is to not have any heated panels on the back of the garment that is in contact with the backrest. You're not losing heat through that area anyway.
I wired my jacket myself from a kit and those were the instructions. The wiring ran down the back from the neck to the shoulder blades but no further.
Ditto... Did the same myself, no heating wire on the back panel..
Fred is also correct, you are risking a fire if you don't size the resistor correctly (wattage) The resistor WILL get hot as well...
 

·
Registered
Joined
·
7,039 Posts
Now we know, Fred is a Electrical Engineer? Liked your DVD's!
 

·
Registered
Joined
·
110 Posts
engineering answer

Jchefboyardee said:
Now we know, Fred is a Electrical Engineer? Liked your DVD's!
If you really want an engineering answer I have one for you.

Use a power mosfet transister to turn on & off the heater several times a second. The mosfet has very little power loss in the on state & none in the off. ergo virtually no power wasted. By varying the on vs off time % you can adjust the power delivered to vest. Simple elegant solution.

Well, you wanted an engineer's solution, didn't you?
 

·
Registered
Joined
·
4,246 Posts
Re: engineering answer

ctgoldwing said:
.... Well, you wanted an engineer's solution, didn't you?
Actually, I think the best answer, in this case, was to not put any wires in the lower back of the jacket.

Your answer, a little bit complex considering the minor problem, would be a close second. The resistor, a distant third ... but simple. :wink:
 
G

·
Alabama IronButt said:
Barn,

I total agree with you analogy. At my age, my mass has declined to the point that the angle of my dangle is mostly downward :shock:
You too, eh? :roll: :lol:

Ride safe.
 

·
Registered
Joined
·
4,823 Posts
Fred H. said:
I don't even remember how to do a Fast Fourier Transform.
Don't feel bad Fred, I don't think any of us do !!
 

·
Registered
Joined
·
747 Posts
you can always add some more clothing in layers.
 

·
Registered
Joined
·
1,004 Posts
I love this board.


I changed a light bulb today..........and when I hit the switch it came on.

I cherish the small victories over electrical circuits :shock: :yes:
 

·
Registered
Joined
·
3,033 Posts
Positive Temperature Coefficient ???

Many heating element materials have a positive temperature coefficient, meaning the resistance to current flow goes up as the temerature of the heating element goes up. It's not usually a linear function. That means there's a chance that you will not get the results you think based on using ohm's law and the E/I/R values you have. You could actually end up having the dropping resistor dissipate most of the heat while the heating elements acted as low loss, create-no-heat, current path at the cooler temperatures. Best to test by putting a variable resistance, potentiometer or rheostat device, in the circuit, and varying the resistance until you get the heating results you desire. Then measure the circuit current and replace the pot with a fixed value power resistor with a wattage based on that current draw.
Hello Fred Harman, I still have that Honda Car CD changer you and I were trying to reconfigure to mate to the goldwing audio system. Some projects just fade away.
DC - Dream Catcher
 
1 - 20 of 34 Posts
Top