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Author Topic: Voltage drop when glowplugs on  (Read 3351 times)

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mark_53

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Voltage drop when glowplugs on
« on: July 16, 2016, 09:05:53 AM »

When I start my M25XP engine and turn glowplugs on, the voltage on the engine panel drops to 10, the lowest reading on my meter. I have a new group 24 start battery. Once the starter failed to start the engine, (no click). I assumed this was because the voltage had dropped to 10v and was not sufficient to start. My question is. Is this voltage drop normal or perhaps a bad glowplug?
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1989 C34 Mk1 M25XP Danforth 25lb, adjustable backstay, fin keel, EV100 autopilot.

Stu Jackson

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Re: Voltage drop when glowplugs on
« Reply #1 on: July 16, 2016, 04:46:47 PM »

10V is normal.  The glow plugs are heavy, albeit short duration load.

No click?:  see the Critical Upgrades - the fuseholder from the key switch to the solenoid.
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Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

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Ron Hill

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Re: Voltage drop when glowplugs on
« Reply #2 on: July 16, 2016, 06:16:19 PM »

Mark : About a 2V drop on the engine panel Voltmeter is about right.  The glow plug is a heating element from resistance load so there will always be a V drop when engaged.

A thought
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mark_53

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Re: Voltage drop when glowplugs on
« Reply #3 on: July 16, 2016, 07:44:41 PM »

Thanks guys, after 27. years it's probably time to change the fuse holder to a blade style.
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1989 C34 Mk1 M25XP Danforth 25lb, adjustable backstay, fin keel, EV100 autopilot.

Stu Jackson

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Re: Voltage drop when glowplugs on
« Reply #4 on: July 16, 2016, 07:49:30 PM »

Thanks guys, after 27. years it's probably time to change the fuse holder to a blade style.

Mark, please read the Critical Upgrades again.  Ken K makes a good point about the fuse being useless at that end of the wiring.  Just connect the two ends, and read the Critical Upgrades.  Did I repeat myself?   :D
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Ron Hill

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Re: Voltage drop when glowplugs on
« Reply #5 on: July 17, 2016, 03:03:13 PM »

Paul : "Thanks guys, after 27. years it's probably time to change the fuse holder to a blade style."

Absouletely !!!!!!!!!!!!!!!!  :thumb:
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KWKloeber

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Re: Voltage drop when glowplugs on
« Reply #6 on: July 17, 2016, 06:28:15 PM »

Thanks guys, after 27. years it's probably time to change the fuse holder to a blade style.

Mark, please read the Critical Upgrades again.  Ken K makes a good point about the fuse being useless at that end of the wiring.  Just connect the two ends, and read the Critical Upgrades.  Did I repeat myself?   :D

Mark, as Stu said, rather than switch that "S" wire fuse to a blade, eliminate it altogether.

Put your effort into this:

Disconnect the #10 awg red harness wire from the solenoid "B" post.
Crimp a M8 tinned lug (not ring terminal) onto one side of an 10 awg ATC/ATO fuse holder wire, butt crimp the other end of the fuseholder wire to your 10 awg red harness wire.  Use the lowest fuse that works - start with 20 amp don't go larger an 30 amp.  if you can't find a 10 awg fuse holder, I can send you one.

You have just saved your boat from an electrical fire that can ruin your day.

kk

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KWKloeber

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Re: Voltage drop when glowplugs on
« Reply #7 on: July 17, 2016, 06:33:10 PM »

When I start my M25XP engine and turn glowplugs on, the voltage on the engine panel drops to 10, the lowest reading on my meter. I have a new group 24 start battery. Once the starter failed to start the engine, (no click). I assumed this was because the voltage had dropped to 10v and was not sufficient to start. My question is. Is this voltage drop normal or perhaps a bad glowplug?

where to start about no-start.  yes 10v can cause it.  Preheat then crank, if you're not set up that way, change it.
If you have OEM #4 battery cables they are woefully inadequate.  - any voltage drop along the way (even on negative cable connections) can drop voltage below the pull-in voltage of the solenoid switch or the starter motor itself.  An undersized "S" wire can cause it.   Need to troubleshoot and upgrade the electrical to eliminate no-start problems.

kk
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

Stu Jackson

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Re: Voltage drop when glowplugs on
« Reply #8 on: July 17, 2016, 07:17:12 PM »


where to start about no-start.  yes 10v can cause it.  Preheat then crank, if you're not set up that way, change it.
If you have OEM #4 battery cables they are woefully inadequate.  - any voltage drop along the way (even on negative cable connections) can drop voltage below the pull-in voltage of the solenoid switch or the starter motor itself.  An undersized "S" wire can cause it.   Need to troubleshoot and upgrade the electrical to eliminate no-start problems.

kk

they are woefully inadequate. 

Not true.  I have been running our boat for the past 18 years with the OEM #4 wires.  I have had a looong discussion with Maine Sail about this on sbo.com.  "Our" conclusions was: It works, but bigger would be better.

No kidding.

Look, if your new alternator's output (AO) (with an eternal regulator) is run to the house bank (and off the C post of the 1-2-B switch) and you either use the switch or an ACR/combiner for your reserve bank, the ONLY uses of those #4 OEM wires are: the electrical distribution panel AND the starter.

The starter is HIGH load, SHORT duration, and Maine Sail did a video on this, which is in the Electrical Systems 101 topic.

It works.  Gee, 30 f-ing years.

If I rewired my boat, I'd put in a bigger wire.

If it continues to work, why should I?

Just so you know, and in the interests of fairness doctrine, Catalina is now putting in 2/0 wire for those runs.
« Last Edit: July 17, 2016, 07:18:31 PM by Stu Jackson »
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KWKloeber

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Re: Voltage drop when glowplugs on
« Reply #9 on: July 17, 2016, 07:43:48 PM »

Stu, what's the approx 1-way length of batt cables on the C34?

Agreed the critical path is starting.  But High load = high v drop.  High V drop and any corrosion drop = (too?) low a voltage at starter.  Low V at starter = no start issues.   

For say 50 amp starter load (a guess,) voltage drop for 4 awg is 0.26v per 1-way foot of length.   Too much for my money unless the batt is fully charged.  Batt not fully "up" makes it a critical issue.

Is it "worth" upgrading? For me it was.  Running #1 awg cables eliminated any issue I had previously with slow starter spin, etc.  That was worth the peace of mind for me, maybe it isn't for your situation or others!

Does 4 awg work, yes.  But not the best.  Does 16 awg "S" wire work, yes.  But not the best.  It's all a matter of degrees and what one's priorities are!
k
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Explore.  Dream.  Discover.   -Mark Twain

Stu Jackson

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Re: Voltage drop when glowplugs on
« Reply #10 on: July 17, 2016, 08:13:49 PM »

Yup, priorities.

Always important.

My LARGEST and MOST IMPORTANT priority is that my engine starts, ALWAYS, NEVER FAILS, NO SUSPICION THAT IT WON'T.

EVER.

In 18 years, it has NEVER FAILED TO START.

I use our boat every week.

Oh, OK, twice, when the stupid fuse/fuseholder failed.  But you've covered that quite sufficiently.

Your boat, your choice.   :D

Just imparting some real world experiences.  NOTHING has changed in the starting system since they built these boats, and the Catalina 30s with diesel engines well before that.

Could it be improved?  Sure.  "Woefully" inadequate?  Hardly.

Is it critical?  Not for me, but could be for some of you.

And using 16 ga as a stalking horse is quite unnecessary, and unrealistic.  It IS #4 wire.  Has been for 30 years on my boat.  Still works.

Your boat, your choice.   :D

I feel like John Denver, slipping in a few "Far Outs!"   :D :D :D

« Last Edit: July 17, 2016, 11:06:25 PM by Stu Jackson »
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mark_53

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Re: Voltage drop when glowplugs on
« Reply #11 on: July 17, 2016, 09:28:34 PM »

When I start my M25XP engine and turn glowplugs on, the voltage on the engine panel drops to 10, the lowest reading on my meter. I have a new group 24 start battery. Once the starter failed to start the engine, (no click). I assumed this was because the voltage had dropped to 10v and was not sufficient to start. My question is. Is this voltage drop normal or perhaps a bad glowplug?

where to start about no-start.  yes 10v can cause it.  Preheat then crank

That's the simplest now that I'm out cruising.  Seems like that should be standard starting procedure if with the glow plugs on you get a drop to 10v...sufficient to cause a no start.  An alternative maybe to wire the glow plugs to the house bank.
« Last Edit: July 17, 2016, 09:30:13 PM by mark_53 »
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Re: Voltage drop when glowplugs on
« Reply #12 on: July 17, 2016, 11:05:36 PM »

Mark, the trick has always been to do the glow plugs first, then RELEASE the glow plugs and only then push start.  No reason to ever have to push both at the same time.  In fact you could wait a few moments in between if you like, since the glow plugs heat up the chambers quite well.  The glow plugs are wired to whatever bank is being used.  Not a good idea to wire them directly to any individual bank.  Why?  You might want to or have to use the other bank.  That's what the switch is there for.
« Last Edit: July 17, 2016, 11:08:26 PM by Stu Jackson »
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mainesail

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Re: Voltage drop when glowplugs on
« Reply #13 on: July 18, 2016, 08:23:27 AM »

What needs to be differentiated is the; battery voltage sag under load and the wiring voltage drop under load. There are TWO different things happening..

When you apply a large load to a lead acid battery the voltage dips or sags. When you apply a large load to the wire you suffer voltage drop. Combine the two and you have the net/net at the starter post.. The smaller the wire the worse the voltage drop. The smaller the battery the larger the voltage sag.. If you measure the positive and negative lead voltage drops, then add them together, this will tell you how much the battery is sagging vs. just the wire...
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mark_53

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Re: Voltage drop when glowplugs on
« Reply #14 on: July 18, 2016, 10:46:36 AM »

If you measure the positive and negative lead voltage drops, then add them together, this will tell you how much the battery is sagging vs. just the wire...

I'm not getting something. How do you measure positive and negative leads?  I measure voltage by connecting the positive and negative terminals to my volt meter.
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