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An off shoot from "How to: Nitrous electrics”
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WARNING: Fuses don't stop fires !
People seem to think 12v electrics can't kill you and fuses can prevent the worst electrician or home bodger setting a car on fire.
You may get away with it for the rest of your life, but when it does go wrong you won't get two chances, car fires burn incredibly hot and incredibly fast.
Even if you had a fire extinguisher to hand, the damage caused in the time it takes to pull the pin is amazing.
Fitting a bottle heater;
The first thing you’re going to do is rip open the box and "give it a quick try" by connecting it to a battery, everyone always does.
It can kill the mat.
Silicone heater mats are intended to get very hot; they're intended to pass all of their heat to a surface.
They are NOT intended to radiate heat; they're intended to conduct heat and without something to take the heat away the fine foil elements inside will burn out.
This can happen in under a minute and shorter times will reduce the power of the mat and reduce the life of the mat.
The silicone material must be kept in full, close contact at all times.
All of it !
Don't let mat overhang the bottle and don't overlap it if it doesn't fit.
But if it doesn't fit don't cut or trim it either, you'll cut the element and stop it working before you even fit it.
(I'm pretty sure "hacking something with a sharp knife" isn't a valid warranty claim or complaint)
The power supply
Like any heater it needs power, quite a bit of power.
A heater than needs as much power as your headlights, heated rear window and heater motor running flat out all at the same time isn't unusual.
So as you can imagine, there isn't a spare wire in your car you can use for this job.
With any luck you've had a stereo fitted or at least an aftermarket amplifier, if you have then you're in luck, check it can take the extra current of the heater and connect the heater supply to either the amplifier fused distribution block or the amplifier itself if there’s enough room at the power terminals.
If you haven’t got an amplifier then we have a slight problem.
We really need (to be on the safe side) a 10AWG or 8AWG cable (5mm2 or 8mm2 cable) running from the battery, through a fuse within 12" of the battery, through the bulkhead (use a grommet) along the floor (avoid sharp edges) and into the boot to a fused distribution block (you could run it straight to the heater, but this gives you a power supply in the boot that’s bound to come in handy !)
Considering the heater wires are only 13AWG (2.5mm2) or sometimes even 18AWG (0.75mm2) this sounds a bit like overkill.
It isn't. For a start the heater wires are often far higher quality than you'll normally find, a 2.5mm2 wire may be "worth" a 5mm2 wire and can easily cost £5 per foot.
Secondly the rating of the wire is industrial, that wire is enough not to burn out when supplied with an ideal power supply at that length.
Every power wire you connect to that heater must be bigger than the wire the heater's fitted with at least.
While you're running wires down the car, run a few 16AWG (1mm2) wires too, they always come in handy at some point and they don't need to be big, they'll only be switching wires because you now have a power supply in the boot.
Wiring it all up
Amongst the electrical connectors, insulation tape and heat shrink you need
(See; “where to get stuff” at the end)
You'll also have to get a standard 4 pin automotive relay, and a dash switch (the reason for this is later)
“Standard” 4 or 5 pin relay’s come in dozens of shapes and sizes, the important detail is the rating, and you need one rated at roughly 20A continuous at 12vDC.
Relays marked “20A” are rarely 20A continuous they’re 20A switch and probably 10 or 15A continuous rated, and you don’t want this failing ! It could just fail in the closed position and not turn off.
(A relay can switch far more power than it can carry continuously, the “relay” (the solenoid) for your starter motor can switch 500A but it can only carry 500A for a few minutes at most)
Try to find one with two ratings like 20/30A
That means it can carry 20A and switch 30A at 12vDC
The dash switch can be just about anything really, it’s only carrying a signal to switch the relay. (as well as the pressure or thermostatic switch for the heater)
The reason we really want a dash mounted switch is for those days when we aren’t using nitrous and we’re just running errands or doing the shopping, if you have your heater running all the time then during these little start / stop journey’s you’ll end up flattening the battery, especially in winter.
Remember, it takes a lot of power and is almost always running for the first 20 minutes of a journey, it can take roughly 20 minutes of running to put back into the battery what starting took out of it, and the heater is already taking between 1/3rd and ½ of your charging output !
Switching:
Connect an ignition controlled live (the nitrous system will have been connected to one) to one side of the dash mounted heater mat switch, connect a wire to the other side of it and run this through a fuse to where the relay is mounted (you see why I said run extra wires now don’t you !)
Connect it to terminal 85 (they have numbers by them)
(I ran it through another fuse, simply because you’re running a live wire through a car and it carries a risk of being shorted out, why take the risk ? A 2.5A or 5A fuse here is fine)
Heater mat:
One wire (doesn’t matter which) should be connected through a suitably rated fuse to the main power cable. If you extend the wire then use wire AT LEAST 2.5mm2 (13AWG)
The other wire is connected to terminal 87 of the relay
Pressure or temperature switch:
Connect one end to earth (look at the back lights, there’s almost always an earth terminal here for the lights, or connect it to the amplifier earth)
Connect the other end to terminal 86
Relay:
We’ve done 85, 86 and 87 so you should only have terminal 30 left (and 87a if it was a 5 pin, forget this one)
Terminal 30 goes straight to a good earth, Use wire AT LEAST 2.5mm2 (13AWG)
The back light earth is ok, but make sure you clean it up and have a really good connection, I prefer to drill a 6mm hole in the bodywork, clean off any paint and clamp a ring terminal to it using a 6mm bolt, washers and locknut.
Setting it up;
I consider you to be a little bit daft if you have a heater and no pressure gauge, without a gauge how will you know it’s up to temperature so you can jet the system properly ?
If you use a thermostatic switch
WARNING: Always make sure the switch makes good contact with the bottle AT ALL TIMES If this switch isn’t touching the bottle properly the heater won’t switch off !
Make this a habit or make a fool proof way of not forgetting, its all to easy to catch the switch wiring and pull it out when you do the shopping or something, don’t forget there may be a day when someone else gets something out of your boot, we all think we’re smart and we all forget other people are idiots.
If you have a pressure switch
WARNING: Pressure switches mounted AFTER the bottle valves can only turn a heater of if the bottle is OPEN !!!
If the valve is closed the bottle WILL over pressurise
Connect a multimeter between the wires on the heater mat (this is so you can see when the switch switches) start the engine and switch the heater on.
If you don’t have a voltage going to the heater mat (and the wirings right !) then you need to screw the adjustment screw clockwise, a little at a time.
Once the heater turns on you have to wait until it turns off again and then see what the pressure in the bottle is. If it’s still too low then turn the screw clockwise again until it turns back on and wait until it turns off again.
Keep doing this until it keeps the bottle at the right temperature.
Let’s just say you set it 850psi, it should switch on at about 840psi and off again at 860psi.
(This would be a really nasty switch having a 1% hysteresis)
Take your time over this, you simply can’t rush it and besides, do it once properly and you won’t ever have to touch it again.
The reason I’ve said have the engine running is the heater will be quicker so you won’t get too bored and you won’t flatten the battery setting the switch !
Ok, you are now the proud owner of a temperature stabilised heated nitrous system.
So make sure you change the jetting of the system to suit the new constant pressure !
(see; How to: Jet a system)
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