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LPWS Glowplug Relay Fuse Rating Advice Please :-)


n.b.Goldie
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The OEM glowplug timer/relay on my Lister LPWS3 has failed for the third time.  It is a Ford part and costs £90 so have decided to replace it with a Durite 120amp relay on a manual switch.  The OEM part is rated at 70amp so I am fairly confident the 120amp Durite will cope.

 

Currently am installing the low tension side from battery to manual switch and would feel more comfortable with a fuse in the circuit.  I think the power requirement for actuating the relay will be fairly low but I can find no info on what it actually is.  My questions are;

 

a) does anyone know the power draw?

b) what size fuse should I install? 

 

My current thinking is perhaps 2amp.

 

c) should I install a fuse from battery to the high tension side going to the glowplugs?  (I think the plugs draw 20amp each and there are three of them so perhaps a 100amp fuse?

 

Thanks in advance

Ditchdabbler

 

 

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3 minutes ago, ditchdabbler said:

The OEM glowplug timer/relay on my Lister LPWS3 has failed for the third time.  It is a Ford part and costs £90 so have decided to replace it with a Durite 120amp relay on a manual switch.  The OEM part is rated at 70amp so I am fairly confident the 120amp Durite will cope.

 

Currently am installing the low tension side from battery to manual switch and would feel more comfortable with a fuse in the circuit.  I think the power requirement for actuating the relay will be fairly low but I can find no info on what it actually is.  My questions are;

 

a) does anyone know the power draw?

b) what size fuse should I install? 

 

My current thinking is perhaps 2amp.

 

c) should I install a fuse from battery to the high tension side going to the glowplugs?  (I think the plugs draw 20amp each and there are three of them so perhaps a 100amp fuse?

 

Thanks in advance

Ditchdabbler

 

 

The only thing I can offer from my LPWS manuals is that the heater plugs are 696 watts

 

LPWS: a 12v glow plug (B) is fitted in each cylinder and a 696 W heater plug (A) is also fitted in the inlet manifold as standard.

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5 hours ago, Alan de Enfield said:

The only thing I can offer from my LPWS manuals is that the heater plugs are 696 watts

60A then. Say a 100A fuse?  If the feed is after the isolator then to meet the BSS it doesn’t have to be fused (which makes no sense to me but that’s what the rules say). 

 

Yes, 2A will be plenty for the relay coil circuit. 

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10 minutes ago, WotEver said:

60A then. Say a 100A fuse?  If the feed is after the isolator then to meet the BSS it doesn’t have to be fused (which makes no sense to me but that’s what the rules say). 

 

Yes, 2A will be plenty for the relay coil circuit. 

The 696w is the manifold heater plug, but (presumably) in the same line are 3x glow-plugs (wattage unknown)

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Forget all that and just fit a land rover discovery glow plug relay £5 for a second hand one on an internet auction site of your choice

 

job done ....

 

That’s what I did I refuse to pay  a hundred quid for a 70A relay with a NE555 timer  

 

the relay timer might be a few seconds shorter or longer  which the lpws isn’t going care about...

 

I think I’m right in saying most just have glow plugs per cylinder and not the 696 w manifold heater plug

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7 hours ago, ditchdabbler said:

b) what size fuse should I install? 

Keep in mind fuse size has to match the wire size, because the fuse prevents the wire from overheating by drawing to much power through it. It is not protecting the device is connected too.

NEVER put a larger fuse size than the wire it is mounted in is rated because is something bad happens it could cause a fire. 

 

Proper way is determine the load needed. Find the proper wire size for that load and then the fuse to match the wire size. 

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Thanks for the thoughts.

 

New relay installed, fused on both circuits, system works well and it appears the voltage drop when the glowplugs are lit is a little less than with the OEM stuff.

 

Regards

Ditchdabbler

 

 

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Hi Ditchdabbler
I may have a similar problem on my LPWS3.
The preheat seems to have packed up resulting in difficult cold starting and a lot of smoke from unburnt fuel.

I've not had a chance to investigate properly yet, but when I turn the key to the preheat position, I can hear the usual loud click as the relay engages, and, less than a second later, a fainter click which I suspect is the same relay disengaging.
Does this sound familar at all?

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4 minutes ago, PaulG said:

Hi Ditchdabbler
I may have a similar problem on my LPWS3.
The preheat seems to have packed up resulting in difficult cold starting and a lot of smoke from unburnt fuel.

I've not had a chance to investigate properly yet, but when I turn the key to the preheat position, I can hear the usual loud click as the relay engages, and, less than a second later, a fainter click which I suspect is the same relay disengaging.
Does this sound familar at all?

I have had three of these highly expensive (£90) and overcomplicated bits of kit fail in the ten years or so I have owned the boat.

 

Two types of failure;

 -the first was that the relay would not disengage, the glowplugs were permanently lit.  I came to realise something was wrong when my 50amp alternator could not keep up with the 60amp draw of the plugs.

-the second was when the relay would not engage and the plugs were then not heated for starting.

 

Of the three failures two were type one.

 

I am not sure why they fail, I did try remounting the relay away from the engine thinking vibration destroying the relay could be an issue but it made no difference.

 

The 'glowplug light' on the instrument panel only indicates when the timer circuit has cut out and its time to crank.  It does not indicate whether the plugs are lit or not.  When its working it appears the relay cuts out shortly after the alternator starts producing power. I have to say I am not entirely sure I am correct about this last bit.

 

I did a few years ago put in a warning light wired and fused directly to the glowplugs as a tell-tale to let me know if they are lit or not.  The second failure was detected when this light came on whilst cruising along.  It also detected the third failure when during start-up the light did not come on despite the timer light on the instrument panel being lit.

 

Hope this helps.

 

Regards

Ditchdabbler

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30 minutes ago, ditchdabbler said:

I have had three of these highly expensive (£90) and overcomplicated bits of kit fail in the ten years or so I have owned the boat.

 

Two types of failure;

 -the first was that the relay would not disengage, the glowplugs were permanently lit.  I came to realise something was wrong when my 50amp alternator could not keep up with the 60amp draw of the plugs.

-the second was when the relay would not engage and the plugs were then not heated for starting.

 

Of the three failures two were type one.

 

I am not sure why they fail, I did try remounting the relay away from the engine thinking vibration destroying the relay could be an issue but it made no difference.

 

The 'glowplug light' on the instrument panel only indicates when the timer circuit has cut out and its time to crank.  It does not indicate whether the plugs are lit or not.  When its working it appears the relay cuts out shortly after the alternator starts producing power. I have to say I am not entirely sure I am correct about this last bit.

 

I did a few years ago put in a warning light wired and fused directly to the glowplugs as a tell-tale to let me know if they are lit or not.  The second failure was detected when this light came on whilst cruising along.  It also detected the third failure when during start-up the light did not come on despite the timer light on the instrument panel being lit.

 

Hope this helps.

 

Regards

Ditchdabbler

Many thanks Ditchdabbler.
I don't have a glowplug light on my panel. I think I'll follow your example and fit one so that at least I can see what is going on.

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