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?
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.
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
Thanks guys, after 27. years it's probably time to change the fuse holder to a blade style.
Quote from: mark_53 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.
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
Paul : "Thanks guys, after 27. years it's probably time to change the fuse holder to a blade style."
Absouletely !!!!!!!!!!!!!!!! :thumb:
Quote from: Stu Jackson on July 16, 2016, 07:49:30 PM
Quote from: mark_53 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.
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
Quote from: mark_53 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?
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
Quote from: KWKloeber on July 17, 2016, 06:33:10 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.
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
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
Quote from: KWKloeber on July 17, 2016, 06:33:10 PM
Quote from: mark_53 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?
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.
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.
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...
Quote from: mainesail on July 18, 2016, 08:23:27 AMIf 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.
Quote from: mark_53 on July 18, 2016, 10:46:36 AM
Quote from: mainesail on July 18, 2016, 08:23:27 AMIf 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.
Measure the voltage at one end of the positive wire and then at the other end. Do the same for the negative. Add 'em up.
Since the starter is bolted to the engine, that creates its ground, so there is no negative to measure.
Quote from: mark_53 on July 18, 2016, 10:46:36 AM
Quote from: mainesail on July 18, 2016, 08:23:27 AMIf 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.
Mark if you get a long test wire, put one end on, say, the battery + terminal, put your meter between the test wire, and, say, the solenoid B post, You are then directly measuring the V difference between those points, and the reading is a direct measurement of the V drop on the positive cable.
kk
Are the glow plugs or starter energized when this measurement is being made?
Quote from: Jon W on July 18, 2016, 09:45:50 PM
Are the glow plugs or starter energized when this measurement is being made?
You can't have voltage drop without current. In order to do this for cranking a meter that can capture fast transient peaks will be best.
Quote from: Stu Jackson on July 18, 2016, 04:05:31 PM
Quote from: mark_53 on July 18, 2016, 10:46:36 AM
Quote from: mainesail on July 18, 2016, 08:23:27 AMIf 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.
Measure the voltage at one end of the positive wire and then at the other end. Do the same for the negative. Add 'em up.
Since the starter is bolted to the engine, that creates its ground, so there is no negative to measure.
Stu,
Confusing...? Did Ohm's law change while I was asleep?? :D Your first line in green is correct. The second line is where the confusion lies.. The
circuit is between the battery and starter. Whether the engine is at Earth potential or not has no bearing on the DC circuits voltage drop and yes the negative side needs to be measured... You can't have a
one-leg positive only DC circuit.
There is still voltage drop between the batt neg and the starter motor thus you can't ignore the batt neg cable because it is part of the 12V circuit for the starter motor. Best to place measure for VD is directly onto the metal case of starter motor and to batt neg to get the actual neg side of the circuits voltage drop....
When measuring voltage drop the most accurate method is to measure both the positive leg and the negative leg. This helps to isolate where the problem may lie. Connect the DVM voltage sense leads to the battery + terminal and then the other lead to the starter post. With zero load you should read 00.00V because
it takes current passing through the wire to create a voltage drop..
(http://www.pbase.com/mainecruising/image/163700504.jpg)
No you set the DVM to peak capture and hit the glow plugs or starter motor and measure the voltage drop on that leg. It may look something like this. If it looks like this with a 40A glow plug load you have issues.
(http://www.pbase.com/mainecruising/image/163700505.jpg)
You now repeat this same test only on the negative side of the circuit between battery
- & the starter motor case. For the glow plugs you can also locally sense at the glow plug busbar and engine block close to a plug or directly on the glow plug body.
Quote from: mainesail on July 19, 2016, 02:41:22 AM
Quote from: Jon W on July 18, 2016, 09:45:50 PM
Are the glow plugs or starter energized when this measurement is being made?
You can't have voltage drop without current. In order to do this for cranking a meter that can capture fast transient peaks will be best.
I learned that in my post a couple months ago and is why I asked. It may be implied, but I didn't see energizing anything in these responses, just measure between points.
Quote from: mark_53 on July 18, 2016, 10:46:36 AM
Quote from: mainesail on July 18, 2016, 08:23:27 AMIf 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.
Another way rather than the direct measurement I posted, would be - measure terminal to terminal at battery, and then measure solenoid B post to starter frame. The difference between the two would be the total loss in the (positive + negative) cables and connections. To determine them separately you need to bypass one or the other and jumper a test wire as I described.
As RC described, whatever you are running (in your case you asked about drop from glow plugs) will cause "X" voltage drop, and a different load (say starter) would cause "Y" voltage drop.
k
Quote from: mainesail on July 19, 2016, 02:44:14 AMNo you set the DVM to peak capture and hit the glow plugs or starter motor and measure the voltage drop on that leg. It may look something like this. If it looks like this with a 40A glow plug load you have issues.
Thanks for the explanation and pictorial view. Not sure what you meant by the above statement. Looks like you left a meter reading off. I suspect it's a DVM meter capable of graphic view of current over time. Would the voltage drop be the difference between the high and low points? I only have a DVM that gives one number.
Quote from: KWKloeber on July 19, 2016, 07:36:15 AM
Quote from: mark_53 on July 18, 2016, 10:46:36 AM
Quote from: mainesail on July 18, 2016, 08:23:27 AMIf 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.
Another way rather than the direct measurement I posted, would be - measure terminal to terminal at battery, and then measure solenoid B post to starter frame. The difference between the two would be the total loss in the (positive + negative) cables and connections. To determine them separately you need to bypass one or the other and jumper a test wire as I described.
As RC described, whatever you are running (in your case you asked about drop from glow plugs) will cause "X" voltage drop, and a different load (say starter) would cause "Y" voltage drop.
k
That will tell you the combination of battery sag and wire drop but it does not really isolate
where the issue is just that there is an issue.. For in-rush type loads ideally should be done simultaneously with two DVM's being used, one at the battery end and one at the starter or glow plug end. Based on what I
don't see aboard boats, I suspect you'd be hard pressed to get most boaters to pony up for just one decent DVM but
two is, well........... If not done simultaneously the battery is now a bit weaker on the second go and the readings will be a bit off a "fresh start". This can cause owners to assume there is more of an issue than there may actually be.
Ideally we want to find or isolate the
issue and the battery can be load tested separately. If the positive wire is dropping .72V and the neg is dropping 1.45V we now where to begin chasing the issues.
Quote from: mark_53 on July 19, 2016, 09:52:09 AM
Quote from: mainesail on July 19, 2016, 02:44:14 AMNo you set the DVM to peak capture and hit the glow plugs or starter motor and measure the voltage drop on that leg. It may look something like this. If it looks like this with a 40A glow plug load you have issues.
Thanks for the explanation and pictorial view. Not sure what you meant by the above statement. Looks like you left a meter reading off. I suspect it's a DVM meter capable of graphic view of current over time. Would the voltage drop be the difference between the high and low points? I only have a DVM that gives one number.
We are looking at voltage drop along a length of conductor using the above test procedure. A good quality DVM will capture and hold fast voltage transients and you can select Peak High Voltage, Peak Low Voltage or an Average. Some of them are fast enough to capture blazing fast solenoid transients. Inexpensive DVM's may not have this feature and you would need to monitor the screen while holding glow to determine max volt drop. For starter max drop you would close seacock, pull stop lever and crank for 10+ seconds or until you have good data.
The high point would be 0.00V or and unloaded circuit. The peak low might be -0.89V at peak current load...
Quote from: mainesail on July 19, 2016, 03:04:36 PM
Quote from: mark_53 on July 19, 2016, 09:52:09 AM
Quote from: mainesail on July 19, 2016, 02:44:14 AMNo you set the DVM to peak capture and hit the glow plugs or starter motor and measure the voltage drop on that leg. It may look something like this. If it looks like this with a 40A glow plug load you have issues.
Thanks for the explanation and pictorial view. Not sure what you meant by the above statement. Looks like you left a meter reading off. I suspect it's a DVM meter capable of graphic view of current over time. Would the voltage drop be the difference between the high and low points? I only have a DVM that gives one number.
We are looking at voltage drop along a length of conductor using the above test procedure. A good quality DVM will capture and hold fast voltage transients and you can select Peak High Voltage, Peak Low Voltage or an Average. Some of them are fast enough to capture blazing fast solenoid transients. Inexpensive DVM's may not have this feature and you would need to monitor the screen while holding glow to determine max volt drop. For starter max drop you would close seacock, pull stop lever and crank for 10+ seconds or until you have good data.
The high point would be 0.00V or and unloaded circuit. The peak low might be -0.89V at peak current load...
I should have mentioned that you needed to monitor the battery also.
I suppose using only one meter you might measure the sag, measure the cable V loss, measure the sag. And for the middle test average and subtract the two battery sags. With all that, it's just as easy to simply use a jumper test wire with the direct method! :D