Autopsy: Infamous "Y" cable from alternator to starter to battery
- Thread starter Deancm
- Start date
There may not be a difference in many cases, but apparently MB makes at least two (2) different Y cables, for the 2 different alternators:
* 180A in the older NCV3 like ours.
* 220A in the newer chassis (maybe 2010 or 2011 and up?).
Had I known that when I replaced ours I would have ordered the Y cable for the 220A alternator. Presumably it is slightly larger gauge, with perhaps a fusible link with a higher rating. The one I purchased is very small -- too small to carry 180 amps without voltage drop.
Combined with the undersized WGO coach wiring from the boost relay to the coach batteries there is a lot of voltage lost.
Increasing the size of the Y cable would at least help some.
I just replaced my battery Y cable and it solved my charging problems. Here's the video I made..
https://www.youtube.com/watch?v=am_uD3rXl6s
https://www.youtube.com/watch?v=am_uD3rXl6s
Good job on the video -- that should help a lot of people!
The job is pretty straight forward, as you said, but I did run into a couple snags that others may experience.
1) The nut was seized to the stud on the starter solenoid -- likely from the excessive heat caused by a resistive connection in the "Y" lug.
When I attempted to turn the nut, the entire assembly (stud/lug/nut) turned. There is (was) a raised portion of the solenoid case that is supposed to stop the lug from rotating very far, but I was able to snap that off without even trying. Oops.
It was then time for my secret weapon -- DW with a crowbar. From the top, she was able to use the bar to prevent the lug and stud from rotating while I removed the lug. There may be a better procedure but that worked for us.
2) The cable has small plastic 'studs' attached to it that are supposed be pushed into holes in the crossmember (and other places IIRC). The position of these 'studs' is fixed (or was on our cable), and in our case a few of them just did not line up with their corresponding holes. Not the end of the world, but frustrating when you pay $68 (at the time) for a small gauge battery cable.
In any case, zip ties may come in handy.
eralimited57
2008 Sprinter 2500 170 Extended High Top 3.0L CRD
I am going to take a look at my Y cable and see if I can't put some insulation around that fuse. I am thinking pipe insulation that is sold at Lowes. I know this stuff only lasts so long before it deteriorates. I would like a more permanent solution if I can think of one assuming I can get to it and put something around it.
I'm not sure that heat is a major issue, but it can't hurt to insulate it.
Search for "exhaust heat shield wrap".
It's obviously not designed specifically for this purpose but might work well.
just replaced mine today.. probably took a couple hours with getting ready and cleaning up.. got a new one shipped from europarts in SD.. Steve's price was half the local dealer.. I try and support the local guys but that was a little to much difference.. I was getting 14.2 volts at the alternator and 13.8 at the chassis battery.. not bad, but I wanted to see better than that..
just as SA pointed out, I think a gorilla put the nut on both the starter solenoid and alternator.. took a little care and got both off without any damage.. my clips would slide with a little encouragement so no problem with alignment of the holes..
with the new cable now I get 14.2 at the alternator and 14.1 at the chassis battery... plus 14.0 now on the house batteries.. not surprised with the the 1/10 drop to the house as it goes through the relay under the passenger seat..
Bernie
2010, 3500 RV
just as SA pointed out, I think a gorilla put the nut on both the starter solenoid and alternator.. took a little care and got both off without any damage.. my clips would slide with a little encouragement so no problem with alignment of the holes..
with the new cable now I get 14.2 at the alternator and 14.1 at the chassis battery... plus 14.0 now on the house batteries.. not surprised with the the 1/10 drop to the house as it goes through the relay under the passenger seat..
Bernie
2010, 3500 RV
Good deal, I'm glad it worked out well for you!
A tenth of a volt drop from alternator > chassis battery and chassis battery > coach batteries seems to be what most people report.
IIRC, I measured about a 0.1V drop on our rig as well. I would not want to see anything more that that at idle with no load. If they are in good shape, the drop across the relay contacts should be very close to 0.0, especially with low current.
Of course it's best to check voltage drop under load, high current. I've been meaning to do that, just out of curiosity.
For some examples, I used this calculator:
https://www.calculator.net/voltage-drop-calculator.html
1) I entered: copper; 1 AWG; 14Vdc; single set of conductors; 5 feet; 1 amp. Voltage drop = 0.0012 volts.
2) All the same except 50 amps. Voltage drop = 0.062 volts.
3) Same except 100A. Voltage drop = 0.12 volts.
I'm not sure if 1 AWG is correct. The Y cable may be smaller. I don't think the one I bought was marked, but hopefully it isn't smaller than #2 AWG.
So we shouldn't really be seeing 0.1 volt with just a small load.
BTW -- I tried moving those little clips on the cable and they wouldn't budge -- they were cinched down tight. I'm glad to hear they moved for you.
vtsoundman
Member
Why don't people get rid of this stupid cable and install a normal fuse mounted to the alternator case & larger cable? There are number of styles that would work just fine...like an MRBF fuse & holder mounted on the alternator case (or small jumper to a fuse holder)...then onto a proper cable? At ~180-200A in hot engine temps housed within a flex loom we really should be at 1/0 or 2/0 cable size...
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Agreed.
I replaced the Y cable once. If the replacement fails I'll be doing what you suggest.
autostaretx
Erratic Member
Thereby demonstrating Ohm's Law: V=I*R ... voltage = current times resistance.
The cable has a fixed resistance, so raising the current by a factor of 100 raises the voltage drop by one hundred.
Rearranging it to R = V/I we can see that your length of cable has 0.0012 ohms resistance.
--dick
will902
Waldo_Sprinter_Van
Hello everyone,
Thought I would share my experience so far...
2007 Freightliner Sprinter 3500
Alternator replaced ~2 year ago (diesel mechanic shop) ~ $700
MB Battery Replaced ~2 months ago (myself) ~ $250
Y-cable replaced ~ 2 weeks ago (MB dealer) ~ $700
Still have battery light light on with no charge (tested at the battery)
Should I take the van back to the dealer or take it to a different Sprinter Specialist altogether?
As a side note...
I’m wondering if my charging system to house batteries is causing a malfunction in the chassis charging system?
I’m running a 300 watt inverter which powers my 70amp fridge and 10amp smart charger?
Thought I would share my experience so far...
2007 Freightliner Sprinter 3500
Alternator replaced ~2 year ago (diesel mechanic shop) ~ $700
MB Battery Replaced ~2 months ago (myself) ~ $250
Y-cable replaced ~ 2 weeks ago (MB dealer) ~ $700
Still have battery light light on with no charge (tested at the battery)
Should I take the van back to the dealer or take it to a different Sprinter Specialist altogether?
As a side note...
I’m wondering if my charging system to house batteries is causing a malfunction in the chassis charging system?
I’m running a 300 watt inverter which powers my 70amp fridge and 10amp smart charger?
Just as a starting point, you could check the voltage both with and without the engine running.
If you check it after it's been sitting for a couple hours, it should be about 12.7 volts.
With the engine running it should be about 14.0-14.1 volts.
One crude but easy way to see if an alternator is working is that at night, with the headlights on, when you switch the engine off the lights should dim noticeably. If the intensity remains the same then the battery is not being charged. Obviously it's better to use a meter, but it you don't have one that's one way to tell.
autostaretx
Erratic Member
Well, i'd certainly *start* by disconnecting the Sprinter-side from the inverter.
Which size alternator did you *originally* have? What size engine? Did you have the "intelligent" battery system?
(these questions can be answered from your datacard, available from https://www.datamb.com/ )
If you have the 4-cylinder (was that an option in 2007?), the alternator system ain't simple, and theoretically requires programmed adaptation to the Sprinter's ECM. Was your "diesel shop" capable of doing that?
Your inverter could simply be subjecting the Sprinter-side to wacky high-frequency varying loads that the Sprinter's systems (IC panel watching system voltage telling LINbus-controlled alternator's regulator what to supply) can't keep up (or gets into "fatal oscillations")
I'd also put an oscilloscope on the Sprinter-side of the inverter just to see what's happening.
(i should do that on mine, too...) Is your inverter "pure sine wave" or just MSW?
--dick
Which size alternator did you *originally* have? What size engine? Did you have the "intelligent" battery system?
(these questions can be answered from your datacard, available from https://www.datamb.com/ )
If you have the 4-cylinder (was that an option in 2007?), the alternator system ain't simple, and theoretically requires programmed adaptation to the Sprinter's ECM. Was your "diesel shop" capable of doing that?
Your inverter could simply be subjecting the Sprinter-side to wacky high-frequency varying loads that the Sprinter's systems (IC panel watching system voltage telling LINbus-controlled alternator's regulator what to supply) can't keep up (or gets into "fatal oscillations")
I'd also put an oscilloscope on the Sprinter-side of the inverter just to see what's happening.
(i should do that on mine, too...) Is your inverter "pure sine wave" or just MSW?
--dick
will902
Waldo_Sprinter_Van
Thanks for your offered advice.
To clarify:
It’s a 6 cylinder 3.0L
No intelligent battery system (option available in 2014 I think?)
The VIN indicates that:
14 V/220 A ALTERNATOR
ENGINE OM 642 DE 30 LA 115 KW (156 HP) 3800 RPM
The output at the alternator is intermittent... one day it puts 14.1V and the next day 11.9V,
Wondering if replacing the Y-cable the alternator was working overtime and is wearing out?
To clarify:
It’s a 6 cylinder 3.0L
No intelligent battery system (option available in 2014 I think?)
The VIN indicates that:
14 V/220 A ALTERNATOR
ENGINE OM 642 DE 30 LA 115 KW (156 HP) 3800 RPM
The output at the alternator is intermittent... one day it puts 14.1V and the next day 11.9V,
Wondering if replacing the Y-cable the alternator was working overtime and is wearing out?
lindenengineering
Well-known member
Where was the alternator sourced from?
Dennis
Dennis
But the NCV3 alternator size/type needs to be the same as the OEM. The T1N could easily swap in a larger alternator. From all that I have gleaned/recall the NCV3 needs to remain as OEM.
Is there any evidence of oil leakage/contamination in the area of the alternator? Oil on the collector rings can result in intermittent brush contact which will affect excitation/output.
vic
will902
Waldo_Sprinter_Van
Oh that could be... thanks for the suggestion. Th last time I replaced the engine oil I incorrectly seated the oil filter cap gasket and had oil come up through the cap and spray the under hood. I’ve been monitoring the alternator and it seems to be working correctly for the past 4-5 days.But the NCV3 alternator size/type needs to be the same as the OEM. The T1N could easily swap in a larger alternator. From all that I have gleaned/recall the NCV3 needs to remain as OEM.
Is there any evidence of oil leakage/contamination in the area of the alternator? Oil on the collector rings can result in intermittent brush contact which will affect excitation/output.
Would a shop be able to diagnose a bad alternator if the brushes were intermittently losing contact?
It seems unlikely that both the orignal and replacement unit are both bad. Alternator output on the NCV3 is controlled via CANbus (acutally LIN bus) so the replacement must be correct for your vehicle. As Dennis and Vic are hinting, where did you get the replacement unit and are you sure that it is the correct item? And is it an OEM/Bosch replacement or an off-brand?
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autostaretx
Erratic Member
11.9 is *really low* ... if your battery was "normal" (say 12.5 v after engine off for a while), i'd hope it would still be noticeably above 12v if the alternator wasn't helping (unless it's been an hour of "not helping"). The alternator/regulator could be doing other "funny" things.
Bad ground strap connections between alternator/engine and frame, or bad negative to the battery should also be checked, as well as the famous Y cable.
--dick