car battery tap

[induction1]

i'm going with the peltier junction under the hood for the im. i have a junction that apparently operates at 12v, 4 amps; is this a significant draw on a 650 cca car battery? what i need to know is how to hook it up. where do i connect the wires and should i use caps and resistors? thanks

 

[Phasor]

It doesn't matter so much about the battery capacity, but instead, the alternator capacity. If the alternator is already heavily loaded, you can end up with a flat battery, but an extra 4A shouldn't normally be a problem.

 

[Klaus]

Tell me what you are trying to do with the 'peltier junction'? 'im' is what?
Peltier junction modules are used for heating or cooling in my experience.

Regarding the 4 amp draw, it won't matter while the engine is running (and the car battery gets charged) but 4 amps WILL flatten your battery if the device left connected for a long time with the engine stopped.
Klaus

 

[induction1]

im is ignition module in my 95 sable. it is tucked into the engine and mounted on the distributor where it gets very hot and when it overheats it causes the car to stall. ostensibly, it cannot be moved so i want to hook up a pj to the im. naturally, it would only operate when the car is on, but i do not know where my main ignition wire is located. the specs say that there is a 68° c temp differential on the pj; does this mean it could possibly get to be 34° cooler than surrounding air temp or what?

 

[Klaus]

Yes, you could use a Peltier module to cool your ignition module but you are fighting a losing battle there under the bonnet.
You are right about the temperature difference BUT, you have to maintain that by lots of insulation around your ignition module and a big heat sink & fan to carry the produced heat away from the hot side of the peltier module. Since that heatsink can easily reach 80, 90 degrees Celsius just from the engine heat nearby you will have to fan away any additional heat generated by the peltier module smartly to get a marginal cold junction side temperature of: under bonnet temperature minus best peltier performance ( this depends how well you insulate the cold from the hot side).

If this is difficult to grasp consider a fridge with the door open or shut. It *does* work better when the inside is well insulated from the outside.
All your wiring to the ignition module will also need to pass this insulation barrier without heat sneaking by or being cxonducted along it.

Peltier junctions *may* perform, under ideal conditions, as your specs say but I doubt that you get better than 40 deg, C between hot and cold side with LOTS of insulation seperating the two and a good heat sink on the hot side. I have played with 75W peltier modules, as size which *might* do something in your case. Smaller ones would be a waste of time IMO. 75W modules take a fair bit of current to run as well.

If the thing is mounted on the distributor, does that mean the heat sensitive part of it also has to stay there? Or, could you leave just the triggering part on the distributor and relocate the HV part elsewhere cooler?
Klaus

 

[induction1]

the module cannot be moved; the car would not run properly, if at all. i'm just looking for 5° here. i know there is alot of ambient heat i'll have to deal with, but if it doesn't work all i have to do is remove it. it's sort of a last option, ya know? what if i made an epoxy enclosure around the hot side of the junction and filled it with water (only a few cc's) and kept it sealed? any other ideas?

 

[mod_critical]

Perhaps you could mount an additional radiator in front of or behind your existing one if there is room. Fill it with water and get a 12v water pump. then pipe it to you ignition module and come up with some creative way to get a lot of pipe surface area to touch the ignition module. I'm not automotive expert, but I used the same tecnique once using an old Buick Regal intercooler radiator in my friend's Grand Am to water cool a subwoofer amp that was overheating in the trunk. It took two a lot of copper piping, drilling, and two pumps, but it got him back in the beat! Anyway if we cooled an _amplifier_ that way I don't see why you couldn't cool anythign that way, including your ignition module

 

[induction1]

that's an idea. probably too much for me though. how small do you think such a cooling system can get?

 

[mod_critical]

I don't know, it depends on the amount of cooling you'll need to get your 5 degrees. Anyway, I bet you could even use a computer liquid cooling system (the processors heatsink on the ignition module, the 120mm radiator in front of your car's radiator). I don't know if that would be enough cooling or how hard it would be to adapt the processor cooler to your ignition module, but always an idea for a small size. Mind you that the computer cooler will be twizce as expensive as picing up an automotive radiator at a junkyard. You can find radiators in junkyards of all different sizes, especially becasue a lot of bigger light duty trucks (Dodge Ram 2500 and F250s and up, and the like) have three or four radiators, one main for the engine, then others such as a transmission cooler, an oil pan cooler, or an additional radiator for the air conditioner. You'll just have to try some thigns and see what works best. (A junkyard will likely let you roll in and take various radiators and dink with them there to see if they will fit the way you want them to.)