Voltage problems

[Deleted account DD]

Thoughts and electrical advice required please,

I'm now onto the the third glow plug in my svo heater in a very short time.

I can accept that the first one was a cheapo put in by the seller and doomed but the second one was a branded Lucas .

Just too much of a coincidence, so I started wondering what was what with them.

Ive spoken to several people who either know their glow plug stuff or have used these heaters and the result is no one has had the similar problems and the plugs should be absolutely fine for what I'm doing.

So I decided to measure the voltage that is supplied to it direct from the battery via the relay.

With the engine running at idle its measuring a steady 14.35V according to my multimeter.

Is this too high? if so is there a voltage regulator I can adjust?

As I see it I'm either incredibly unlucky (see how long the bosch thats now in lasts :nenau) or too higher voltage is screwing it up. I suspect the latter.

Cheers :thumb2

 

[Terranosaurus]

After running for a while (ie you've charged the battery up) you should be getting siomewhere in the region of 13.8 - 14.2v.

So you're only a tad over. But if you're getting that imeadiately after start up then there is definitely a problem.

 

[tezzer]

definately seems to high.

 

[ssteve]

14v sounds fine to me, 24v systems often charge at 28v plus

ssteve

 

[ssteve]

oh and lucas is not the lucas we used to know,it's just a name now bought by some company and churning out cheap parts,

ssteve

 

[Toolbox]

Never really considered this before but, I wonder what the life expectancy of a glow plug left on all the time is? Is it getting to hot not having enough heat transfer to the oil?

 

[Toolbox]

Is it only heated by the plug or does it have a water heater that takes over when the engine warms up?

 

[aggas]

Thoughts and electrical advice required please,

I'm now onto the the third glow plug in my svo heater in a very short time.

I can accept that the first one was a cheapo put in by the seller and doomed but the second one was a branded Lucas .

Just too much of a coincidence, so I started wondering what was what with them.

Ive spoken to several people who either know their glow plug stuff or have used these heaters and the result is no one has had the similar problems and the plugs should be absolutely fine for what I'm doing.

So I decided to measure the voltage that is supplied to it direct from the battery via the relay.

With the engine running at idle its measuring a steady 14.35V according to my multimeter.

Is this too high? if so is there a voltage regulator I can adjust?

As I see it I'm either incredibly unlucky (see how long the bosch thats now in lasts :nenau) or too higher voltage is screwing it up. I suspect the latter.

Cheers :thumb2

In the idle, you must see in your multimeter a range between 11,8 - 12,4 volts. When you increase the rpm of the engine you must see a range between 13,5 - 14,2. This is the propper voltage from the alternator to overcome the battery's voltage to charge it. If in the idle you are reeding 14,35 that means one diod on the regulator is off. All you have to do is to replace the regulator.

 

[Deleted account DD]

Thanks all :thumb2

My car electrical knowledge is very rusty and whilst i expected more than 12v I didnt know any more :bow

in answer to points made.......

The glow plug is thermostatically switched and heats up a metal block which the svo passes through. Its surprisingly efficient and (being a bit sad ) I put a tell tale light onto the glow plug watched how often the glow plug is working, its not that much, definitely not on all the time :thumb2

My first thoughts were as toolbox mentioned , life span if it was on all of the time. The first one went after about 1500miles of driving. When I asked folk who know about this sort of thing they told me that even if it had been on all the time over that period of time it should have survived quite easily :thumb2

Steve.I presumed lucas was still decent Lucas and not cheap far eastern pattern stuff......most disappointed.......so the Lucas may have been an even cheaper and nastier one than the original

Aggas thanks for the figures, is the regulator an easy replace? I take it its 100% diode pack and not an adjustable regulator fitted (so I have no get out :augie )

Again thanks all :bow

 

[ocelot]

if the voltage is too high, you could always put in a current limiting resistor capable of say handling 200 watts, depending on the load, which I guess will be in the range of 10R.
The idea is to limit the current going through the plug, you'd get a small volt drop depending on the value of the resistor which I'd guess to be around 4 or 5 ohms. It'll get hot but then it should..................

 

[Deleted account DD]

if the voltage is too high, you could always put in a current limiting resistor capable of say handling 200 watts, depending on the load, which I guess will be in the range of 10R.
The idea is to limit the current going through the plug, you'd get a small volt drop depending on the value of the resistor which I'd guess to be around 4 or 5 ohms. It'll get hot but then it should..................

cheers, I've literally just been sitting here after my last post doing the good old W=A x V calculations.

I know the glow plug is designed to work at 12v 170watts so the current is just over 14amps. therefore to maintain that at 14v (seeing as everything else appears ok) for now at least using V= I x R a 10p around 2 ohm resistor in series sounds about right? ??????

Would you agree or would I be better using a higher value you mention to put less load on the heating coil?????

:thumb2:bow

 

[Deleted account DD]

Or getting even smarter, a variable pot in series? £2 or less off the shelf from maplins then adjust it down and try out different voltages/currents

:bowcomments pls folks :bow

 

[ocelot]

cheers, I've literally just been sitting here after my last post doing the good old W=A x V calculations.

I know the glow plug is designed to work at 12v 170watts so the current is just over 14amps. therefore to maintain that at 14v (seeing as everything else appears ok) for now at least using V= I x R a 10p around 2 ohm resistor in series sounds about right? ??????

Would you agree or would I be better using a higher value you mention to put less load on the heating coil?????

:thumb2:bow

If we use I=P/V,
170 watts divided by 14 volts dc, we get the current to be around 12.1 Amps.
Now we can work out the DC resistance of the circuit, using R=V/I which if we divide 14vdc by 12.1 gives us 1.157 ohms.
So we add a 2R resistor to the load in series, giving us a total load of 3.1 ohms, that's a little on the high side, as you need current to heat the plug.

You'd be better off with a 0.5 ohm resistor, The wattage across both devices would be in the region of 350w so you'd need a 200 watt resistor, (bolt it to a heatsink) depending on the power dissipation in place at the moment.

You'd also reduce the current to around 8A which should give you more life in the plug............

Hope this helps..

Dave

 

[rustic]

:nenau:nenau:nenau

Or getting even smarter, a variable pot in series? £2 or less off the shelf from maplins then adjust it down and try out different voltages/currents

:bowcomments pls folks :bow

A good way to waste £2 this will burn out as soon as you fit it. For this current 14 Amps you will need a variable resistor (Rheostat) capable of taking several hundred watts, not something that maplin would have for £2.

Placing a resistor in series with the alternator will only limit the current anyway.
When the battery is nearly fully charged, then the current will drop and then the voltage will rise to the terminal voltage of the alternator.
This will over charge the battery, and damage any electronic equipment, ECU Radio, even bulbs and the regulator for the instrument panel will over heat.

Fix the alternator. Problem solved.

 

[jims-terrano]

Doubt you'd get a POT heavy enough to runthat kind of current without burning out.

Just take a step back a little and think about your possible over voltage and worry about that first What else could it damage Investigate this first if I were you.

Don't think we can buy a seperate Regulator for our alternators, you may well have to buy a whole alt instead which is pots of money

Jim T

 

[ocelot]

I agree, fix the alternator is the best option, and if its just a diode, then it's simple enough.
The basic fix I've underlined won't effect the charging circuit, nor will the battery be damaged, the only thing it will do is limit the current going into the plug. Nothing more or less. So as a temporary fix, it'll work but the best fix is to get the alternator diode pack fixed. If it's not an epoxy enclosed black box, you could find the duff diode and replace it, if that's what it is.
You should see the voltage rise to a maximum of 14.2vdc on starting the engine, it should then drop to 13.8 to 13.2 depending on the charge circuit, with the engine off, the battery should drop no lower than 12.4vdc after an hour with little or no load. If it does, either you have a current drain or the battery's goosed

 

[rustic]

Doubt you'd get a POT heavy enough to runthat kind of current without burning out.

Just take a step back a little and think about your possible over voltage and worry about that first What else could it damage Investigate this first if I were you.

Don't think we can buy a seperate Regulator for our alternators, you may well have to buy a whole alt instead which is pots of money

Jim T

Hi Jim, looks like we are both onto the same issue.

 

[rustic]

I agree, fix the alternator is the best option, and if its just a diode, then it's simple enough.
The basic fix I've underlined won't effect the charging circuit, nor will the battery be damaged, the only thing it will do is limit the current going into the plug. Nothing more or less. So as a temporary fix, it'll work but the best fix is to get the alternator diode pack fixed. If it's not an epoxy enclosed black box, you could find the duff diode and replace it, if that's what it is.
You should see the voltage rise to a maximum of 14.2vdc on starting the engine, it should then drop to 13.8 to 13.2 depending on the charge circuit, with the engine off, the battery should drop no lower than 12.4vdc after an hour with little or no load. If it does, either you have a current drain or the battery's goosed

On other vehicles where a diode has gone, the diode has discharged the battery at the rate of 3 amps, so overnight the battery could be flat, and if left like this then you will need a new battery. Worth checking.
Also how accurate is the multimeter, a cheap one can be 5-10% error especially as the battery in it gets older.

 

[Timbo_1975]

Thoughts and electrical advice required please,

I'm now onto the the third glow plug in my svo heater in a very short time.

I can accept that the first one was a cheapo put in by the seller and doomed but the second one was a branded Lucas .

Just too much of a coincidence, so I started wondering what was what with them.

Ive spoken to several people who either know their glow plug stuff or have used these heaters and the result is no one has had the similar problems and the plugs should be absolutely fine for what I'm doing.

So I decided to measure the voltage that is supplied to it direct from the battery via the relay.

With the engine running at idle its measuring a steady 14.35V according to my multimeter.


That is only slightly higher than I would expect, certainly not high enough to cause problems. Besides, I would almost certainly guarentee that the voltage seen at the g/plug will be lower than this due to the resistance in the wiring...

Take a reading at the g/plug and let us know what it is...

tim.

 

[Deleted account DD]

Tim, its exactly the same as at the pos terminal :thumb2

The wire is only about 40cm long and goes from the terminal to the fuse, then through relay, then thermostat and then glow plug :thumbs

I agree with those who say to fix the alternator but the thing is, the voltage is on the high side but not way over and as everything is supposed to be able to hack the high side :nenau if i could get a new reg cheap, no problem but I could see an alternator being expensive .

If there were no backwards problems I fancy the resistor as an option the logic being its already presenting a resistance as its a coil in a metal cover :nenau

Please keep the advice coming its all very much appreciated :thumb2