voltage drop/ how to test glow plug on bmc 1.5

[lexicon]

How much voltage drop would you expect on using glowplugs.

And how can they be checked easily?

[Sir Nibble]

Give me the glow plug's resistance, hot and cold, Cable resistance and the internal resistance of the battery and I will work it out for you. Between which two points are you interested?

[Taslim]

On my van the lighter socket volt meter drops for about 12.3 to 11.5 as the pins warm.

 

Checking I use a clamp amp meter. start at the 'far end' and clamp your way to the feed. You should get a slight current increase at each link.

[Tony Brooks]

Typical 1.5 plugs draw about a steady 6 amps each but different makes vary. Typically assume a total draw of 24 amps steady for most 1.5 pin type plugs while 1.8 type plugs seem to draw about 12 amps each once the have warmed up. This figure seem to vary more than the 1.5 figure. As base point on a 1.8 expect around 100 amps or more when cold and very quickly dropping to 50 amps for the set.

[lexicon]

Thanks all.

 

I ask as engine hard to start now the cold weather is here. And only get a drop to 11.5v on voltmeter when I have the heaters on.

[Dutchie]

You can try also a direct current from the battery , together with AMp. meter it will be +/_ 8 Amps for 1 heater , it is possible that there is a bad connection (resistance) in the normal circuit , bad connection , wires and contact switch.

Edited January 5, 2016 by Dutchie

[Tony Brooks]

Thanks all.

 

I ask as engine hard to start now the cold weather is here. And only get a drop to 11.5v on voltmeter when I have the heaters on.

 

If that is on the boat's voltmeter it suggests a battery or wiring fault to me. You are dropping about 1 volt with around a 25 to 32 amp load (see mine and Dutchie's posts). If it is from a hand held voltmeter connected to the glow plug cables then it sounds more like a cable/connection problem or a burned contact inside the ignition switch.

 

What are you getting on the voltmeter with the glow plugs on and cranking? It could be down around 8 volts indicating a flat battery or a staring circuit fault and a discharged battery would crank slowly giving poor starting.

 

Apart from some vague kind of idea the glow plugs are working you can not use voltdrop to tell anything about the plugs themselves. Volt drop only tells you about the ability of cables and connections (including the parts inside the battery) to carry the load.

[lexicon]

Engine spins over fine and fast. Engine will eventually fire and sounds like on 3 cylinders. Then all shortly after.

Has recently been rebuilt with new pistons etc.

[Tony Brooks]

Engine spins over fine and fast. Engine will eventually fire and sounds like on 3 cylinders. Then all shortly after.

Has recently been rebuilt with new pistons etc.

 

I wish I had a pound for every time I have been told this only for it to be later disproved. Not saying you are wrong but in the absence of the cranking voltage there is no way of knowing.

 

You could try disconnecting each plug, get someone to hold the key in the heat position and then "flash" the disconnected wire across the terminal of that single plug. If the plug is drawing current you should see a small spark. Better still connect a voltmeter between the disconnected wire and each plug. If the plug wants to draw current you should get a reading of battery voltage. This does not prove the plug is working, it only proves it is drawing current.

 

It is still not clear where the original voltage reading was taken from. This is important because of what I said in my previous post.

[lexicon]

Cranking voltage about 10v

Taken on instrument panel voltmeter.

[Tony Brooks]

Cranking voltage about 10v

Taken on instrument panel voltmeter.

 

That's good, just within the Lucas spec.

 

Was the 11.5 v taken from the same place? It seem rather low with such a load so I am wondering about an undersized cable between battery and ignition switch, poor connections on that like of restive ignition switch. I would try turning the ignition on add bridging the main feed to glow plug terminal on the switch. If you read a lesser voltdrop the switch contacts are suspect.