Starter solenoid switching

[merc-blue]

I have been looking at the wiring in my 71 TA22 recently
A new "racing" dash panel is going in and I'm thinking a push button starter would be cool,
the question is though, origionaly there is no relay or anything switching the starter from the ignition does that mean i can just replace it directly? or while changing wires would you chuck a relay in aswell?
the buttons im looking at are rated at aprox 10A at 100V, which to me would be enough there is no way my ignition switch is switching 10A

any tips would be appreciated

[roadsailing]

just replace the standard key switch with the strarter button, you should have zero problems, the starter relay is in the engine bay on the exhaust side.

[merc-blue]

ok, the relay isnt pictured in the wiring diagram thats all

[Mos]

To my knowledge virtually nothing pre early 90s (except maybe MR2s) had starter relays from the factory.

I would add a starter relay without even thinking about it, even if you have no problems now. It's like head studs - relay is an engineer's decision, lack of is the accountant.

Your ignition switch is likely to be rated at a lot more than 10A - possibly 30 or 40 - however the starter contact isn't used continuously so it may have smaller contacts.

Mos.

[jonra23]

You don't need a relay in the starter solenoid circuit, all you are doing is energizing the solenoid coil, which does'nt take much power and isnt loaded for very long.

regards
jon

[roadsailing]

not that it has anything to do with the original post, but:

a starter solenoid draws a respectable amount of current, it is a bigtime thing. I know for a fact that my car has a relay to operate the solenoid, and it's a safe bet it was there from factory.

the reason merc-blue doesnt have to worry is because there is already a solenoid there!

[merc-blue]

if my ignition has been doign it for 35 years im sure the new button should do it for 10,

cant there be a easy majority answer

[roadsailing]

everyone agrees that you can do it no probs, just for different reasons.

have a quick look in your engine bay, trace the thin wire from your starter motor back and see if it goes to a relay.

have a look at the switch triggered by your key, compare it to the switch you are putting in.

[JetspeedCamry]

Even if the system doesn't have a relay, it doesn't hurt to add one. I've added one to mine because heat was starting to affect the solenoid, so i'd be having to wait till she cooled off before it triggered. The relay fixed this problem.

[Mos]

To clarify, I'm not saying it won't work without a relay, I'm just saying it's better with a relay.

However, if the switch you are using is of cheap quality (and the majority of starter switches on the market are of cheap quality) then it might work for 6 months, then start being intermittently unreliable, eventually failing.

The starter solenoid on a 1G-FE draws a touch under 8A continous - the initial hit is higher. There are two solenoids inside a starter solenoid, one high current "pull" solenoid, and another low current "hold" solenoid - the 8A is the low current hold solenoid, I don't have an easy way of measuring the high current solenoid right now.

The cabling on a factory starter solenoid circuit uses cables capable of carrying around 30-40A continously - IE they are thick.

On a factory system without a relay you have somewhere in the order of 3 or 4 metres of cable carrying the current to the starter solenoid. On a mass production level, an extra few metres of wiring is a lot cheaper than a relay.
On a TA22, this cabling runs from the battery, across the front of the engine bay, under the driver's side guard, to the ignition switch, and back under the guard and around the engine bay to the starter motor. (The cable running from the battery also supplies everything else in the car, including the wipers, blower, ignition coil, etc, at some point joining the alternator). In addition, on a 1971 TA22 this wiring is 35 years old!

Using a relay, this (high) current path can be cut down maybe less than a metre if you select your routing well.
Now in addition if you have relocated your battery to the boot, you will have even more cabling in the path.

Starter motor teeth do not always engage directly with the ring gear on the flywheel. The teeth are chamfered to promote rotation and allow engagement. In a number of circumstances the solenoid may not have enough force to push the starter gear into the ring gear. In some of these circumstance having a more direct current path using a starter relay helps overcome some mechanical problems commonly found in older starter motors - ie dirt, inadequate lubrication, etc.
If to these circumstances you add things like a weak battery everything starts going downhill quickly.

So while I don't entirely disagree with jonra23 - you don't *need* a starter relay if everything is "normal" - I'm of the firm (professional?) opinion it is *better* to fit one, because it covers you for situations when things are NOT "normal".
The choice is entirely up to you.

Mos.

[ViPeR_NiPPleX]

I agree with ya Mos, plus its much easier to replace a relay than a switch when the time comes!

[jonra23]

Choice is yours and dont disagree with what the others are saying, a relay is a more correct and elegant wiring solution.

If you are building a competition vehicle the less you have the less can go wrong so I like the the KISS principal, if not running EFI only need about 7 wires and a couple switches to start and run an engine including charge circuit, plus a couple if you want to run temp and oil pressure warning lights.

Switch that I have used fair few times before in competition vehicles and on earthmoving equipment is at http://www.hella.co.nz/?t=9&pcid=256...=429&View=Full

regards
jon

[bansheebuzz]

That is a "cole hersey" style of switch. The only switch i would use if not running a relay.