Beefy AUX alternator installed. No power pulling away, then surge of power. Normal?

WT1J

Member
Hi all,

2021 Sprinter 3500XD 4x4 170" wheel base with MBUX package. Rear of the van is an empty metal box without anything in it. We're turning it into a film truck.

I'm new to sprinters so I wanted to check if this is normal. We're still gathering data on the issue, but so far, here's what we've done and what we are seeing:
  • We installed a 10Kw power system that is 24 volt DC in the van.
  • Part of the install was a 24 volt auxiliary alternator that provides over 3KW of charging to the house batteries. The alternator is a Nations 24 Volt 150 amp alternator. (AD-24V-150-ERL)
  • With no charging: When pulling away from a standing start, the sprinter pulls away slowly, then without moving the throttle position it hits a power band and really takes off.
  • When charging house batteries and the alternator is producing 70 to 130 amps, there is less power.
  • When the back wheels are in a bit of a ditch, I actually can't pull away. I put the throttle all the way to the floor and the Sprinter doesn't move. Had to engage low range to get her moving today. Have not tried the same ditch without charging.
As I mentioned, I'm still gathering data on this and part of what I'm trying to do is reliably reproduce the problem under various conditions. I also haven't read the Sprinter manual from cover to cover yet.

But I thought I'd start a thread and find out whether others have seen this when installing a second alternator? Or if this is perhaps an unrelated issue?

Is there any known recalibration of the ECM or another component to let the van know it needs to make more power sooner at idle?

The vehicle is brand new and we only received it a few days ago, so I'm sure we'll have much more data as the week progresses.

Thanks,

Mark Maunder.
 

RVBarry

Well-known member
Hi, you might try disabling the traction control for the ditch. (ASR)
 
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Eric Experience

Well-known member
Mark.
How are you driving this 2nd alternator?, the power you hoping for is impossible without modifying the front pulley. How are you exciting the alternator? Eric
 

VanGoSki

Well-known member
Mark.
How are you driving this 2nd alternator?, the power you hoping for is impossible without modifying the front pulley. How are you exciting the alternator? Eric
I've seen my nations alternator put out 160 amps at 12V at idle with the stock pulleys. That would be the same power as the OP's 24V alternator at 80 amps. In my normal state I have it limited to 100 amps, but I have no problem at all pulling that at idle.

The hesitation coming off the line sounds like the standard turbo lag. It's normal but annoying. I agree with @RVBarry on turning off ASR traction control for the ditch thing. It may be that you're actually spinning a wheel when that happens which causes the ASR to apply braking.
 

brianzoh

Member
The slow off the line then off you go sounds entirely consistent with what I experience as just a normal day-to-day in the Sprinter. I also have a 3500XD but in RWD and upfitted. I've had the beast down a good dirt slope and hit the accelerator and ... nothing. I had to give it a bit of an angle to the slope to get the RPM up just a little and then it was fine.

If you aren't experiencing wheel spin and the RPM isn't going up I don't know what to tell you. At least you have 4WD to compensate.
 

WT1J

Member
Mark.
How are you driving this 2nd alternator?, the power you hoping for is impossible without modifying the front pulley. How are you exciting the alternator? Eric
Hi Eric. I didn't do the install myself, although I've installed alternators before. AFAIK the guys just installed it and added a new belt which routes around the alternator wheel. I'm posting a follow-up so please see below. Thanks.
 

WT1J

Member
I have updates!!

Firstly, the good folks at AM Solar in Oregon installed the power system with the beefy 24 volt 150amp Nations alternator. Mitch and the team there are amazing - sorry but I have to give them kudos. They've installed a 10KW prototype system (two inverters working together) for us with custom metal cabinet and 19,200 available watt hours. (Yeah that's not a typo)

Chatting with Mitch who installed the alternator, not only does the alternator have a switch to disable it from generating any load, but he was kind enough to route wires for that switch through the firewall for me. I verified that breaking the circuit makes the alternator output zero current.

Then I left the alternator disabled and took her to Mercedes in Littleton, CO and we went for a test drive. They verified the van is performing normally and it's just normal turbo lag.

The performance we're seeing from the van at this point with the alternator disabled is normal.

With the alternator enabled, she is a little slower off the line, and she may have issues pulling away on a slope, although as some have pointed out that may just be traction control. I have also verified that I'm able to pull away on inclined dirt in low range, so that's a backup plan.

The alternator when it is engaged generates over 3000 watts continuously which is amazing.

So what we're going to do is route the alternator switch to the OEM switches in the dash. Then when she's just idling, we'll engage the alternator, or if she's on the highway cruising at 65Mph on level we'll engage it then. If we need power, we immediately disable the alternator.

I think this solution will work well because it gives us massive power for the house batteries straight from the diesel engine, but we can give that power back to the engine with the flip of a switch.

Thanks everyone for your input. Feel free to call bullshit on my thoughts - but at this point I'm feeling like we're in a good place. Only unknown is the longevity of pulling 3kw from the engine with the aux alternator, but I guess we'll find out sooner or later. :giggle:

Regards,

Mark.
 

Eric Experience

Well-known member
Mark.
There are problems with this set up, Look up any engineering hand book and see how much power you can drive with a single A section pulley 100 diameter. Eric.
 

WT1J

Member
Eric, there are quite a few variables in that calculation. I appreciate your concern, but is there a specific failure mode you're anticipating?

In general the engine produces 140KW and I'm drawing off about 4.2KW with both alternators - which we can round up to say 5KW due to losses. So around 3.5% of available power. But it sounds like you're concerned about mechanical failure e.g. belt, wheel, bearings? or something else? The alternator was built by Nations specifically for this van and as an auxiliary, so if there is a concern here I'd like to take something specific to their engineers.

I noticed in your earlier comment you mentioned "the power I'm hoping for". The alternator is actually delivering over 3KW to the house batteries - I have realtime telemetry on the power input and it produces a range of around 1500W to 3200W over an hour trip and does a great job of charging them up. So it's doing its job. This thread was really about concern around the van engine performance, but I've largely solved that at this point with a few bits of info and changes:
  • I think the traction control was the issue when in the ditch.
  • The switch to turn the alternator off immediately recoups the power that the aux alternator was consuming and hands it back to the engine. So that's an excellent option in case we have an issue.
  • The "surging" in van performance pulling away is normal according to MB service who has now driven the van. It's just turbo lag which is more pronounced at altitude.
I just drove the van on regular paved roads for 40 miles and it charged up the batteries fine while having enough power to drive. I've rigged a switch and tested turning it off and on during the trip and it worked great.

Thanks.
 

Eric Experience

Well-known member
Mark.
You stated in your first post that you are running a 10kw system, clearly you are not, but that triggered my bullshit filter. An A section belt will not handle the power for very long, the sprinter crankshaft rotates in a series of pulses causing stress on the drive, this is overcome with a sprag clutch on the factory alternator, a sprag on you new alternator would extend the life of the drive. Eric.
 

WT1J

Member
The system is 10KW - in other words the dual inverters can produce 10KW peak and 8KW continuous. See attached photo. And I did mention directly below that, in my original post, that the alternator is 3KW.IMG_5854.jpg
 

Eric Experience

Well-known member
Mark.
Now I see what you have, it is two 5 k systems, fair enough. hope you get the pulley sorted before it goes bad. Eric.
 

autostaretx

Erratic Member
Just as an arm-wave to scale the issue for other readers, a 3KW alternator is (idealized) 4 horsepower. (1 HP= 750 watts)
Toss in another 50% for "losses" and you're at 6 HP.

Belt systems tend to have (somewhere) specifications on the HP they're designed to supply at maximum load.
I've seen 6 or 7 HP specified for the T1N Sprinter.
If your 2nd alternator is being driven by a 2nd pulley on the original alternator (versus a double pulley on the end of the crankshaft, which is how MB does it when you order the "power take-off package"), then the original belt is being asked to deliver the total of the two loads: its normal bunch (alternator, AC pump, water pump) *plus* the 2nd alternator. Expect short-lived belts if that's the case.

--dick
 

WT1J

Member
Thanks Eric. Thanks Dick. I found this post explaining sprag clutches.


It explains the inertia of the alternator and that the clutch allows the alternator to spin rather than push back with its own inertia.

Things I think I need to figure out (based on my newbie understanding at this point):
  • Is my aux alternator on the same serpentine belt as my other alternator, or a separate pulley/belt? Visual inspection should clarify this I'd think.
  • Does either alternator have a clutch? Sounds like I can remove the belt and hand spin both alternators in either direction to determine this.
  • Can I install a clutch on both alternators of neither have one, which may reduce belt wear at idle and also during normal driving?
If you good folks have any articles on how to install a sprag clutch in a VS30 I'd very much appreciate any suggestions. I haven't begun googling in earnest just yet.

Thanks for the help!! This forum is really great.

Regards,

Mark.
 

VanGoSki

Well-known member
Mark,

Nations has a couple of belt options. However for their 24V alternator they only support their 3-belt kit. A normal Sprinter has two belts, and Nations adds a third belt dedicated to the aux alternator. So you should see three belts in there.

Nations has what they call "decoupler pulleys" which I believe are the same as a sprag clutch. My Nations 12V alternator has this and it's called out on its webpage. Their 24V page doesn't explicitly call out the decoupler pulley but that could be an oversight so you could contact them and ask. Or pull the belt off like you said and see for yourself.

I don't know whether the stock alternator uses a decoupler pulley or not, but I personally wouldn't mess with it. MB knows best, not to mention you could have warranty issues to deal with down the road if something related fails.
 

WT1J

Member
Thanks Van. Appreciate the data. I did see their decouplers earlier today after reading the latest responses here.

I have some additional data and photos. Firstly, the Nations aux alternator does have it's own belt that is separate from the van's own serpentine.

The aux alternator belt is green. The serpentine is black in these photos. Also, the front of the van is up in all photos I'm including. The photos are taken from the underside. The aux alternator is pretty much the lowest part of the engine assembly. The driver side of the van is the right side of the photos. The aux alternator is located on the passenger side. Just to help you orient yourself.

The aux alternator visually does not appear to have a clutch (decoupler) wheel. It looks to me like a regular black pulley wheel, but I'm a novice in these things. I'm not able to verify whether it's a clutch without disconnecting the belt because the engine is holding the belt firmly in place.

Photos follow: (edited for clarity)
 

Attachments

WT1J

Member
I think the most helpful bit of info I could get at this point is knowing if that Nations aux alternator has a clutch on it currently. So any thoughts based on the above photos would be appreciated. Apologies for the multiple posts - there was a limit on attachments, and I thought I'd follow up to clarify what I'm after.

Thanks,

Mark.
 

WT1J

Member
Thanks. Definitely a clutch pulley. Googling the model number brings up quite a few sellers:


Mine does not look at all like a clutch. I'll give Nations a call and see if I can add a clutch to my aux alternator.

Thanks again!!

Mark.
 

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