Change idle rpm on QSB?

[Jon Fitch]

I have a QSB 5.9, idle is set to the standard 600. Can it be set up using the Cummins Insight software (or some other means)? I do not have the C-Cruise option.

The alternator cannot keep up with the draw at that speed and I get low voltage warnings. At about 675 it is break even and no problems, so I’d like to get it set to 675. I’ve called two Cummins service reps and they don’t seem to know how.

Topic

[Jon Fitch]

If you can fit a smaller pulley without over speeding the alternators, that’s probably the easiest/cheapest route. I’ve run out of time to chase this but I think my ultimate solution involves a hair pin stator alternator, either Balmar’s or someone else’s. The Delco 24 and 28 are similar to the hair pin style.

[john]

I’m finding this post very interesting. This week I went Through the charging systems on a 42 duffy with a similar problem, It is equipped with twin large frame Balmar alternators with there ars-5 regulators. He has had charging issues at idle trolling salmon since he has owned the boat. Tons of shit to power on this boat. Isolated charging systems also so you don’t get both alternators powering the house system. I worked with Balmar and concluded that the start up point is right at the low rpm Setting at 600 rpm. It varies a bit from each alternator. Seems odd to me but it sure acts like that. I might try a smaller pulley. The engines are c9 cats so they are electronic so I’m sure raising the idle will be a software thing that cat will have to come out. Another option is a hair pin stator alternator.

[Philip]

Maybe a few good pictures of what you have now will allow us to recommend what you will need.

Phil

[Jon Fitch]

Not what I’m talking about, that is the tension idler. It doesn’t care what alternator is on there. The tension arm I’m talking about is the one that in the old days had a slot to set the belt tension. Now it’s just another arm to hold the alternator on.

[Philip]

Tensioner

https://www.sbmar.com/product/cummins-belt-tensioner-with-bolt-qsb-59/

[Jon Fitch]

That’s remote oil filter.

Also, is there a tension arm that works with the QSB and 28si alternator? I had to fabricate one for the Balmar and could do it again, but it was a pain to do on the boat away from my machine shop.

[Jon Fitch]

Will the 28si fit on an early QSB? It looks like I’d have to swap the alternator mount to the J180 and also remove the remove oil filter as the lines are very close to the original small alternator.

[Tony Athens]

Hot Rod Delco small frame Balmar Alternator

http://www.balmar.net/product/alternators/alternator-94-12-210-ig/

Is this what you have? Based on an old 15SI unit

These designs only start making “amps” above 2500 alternator shaft RPM, and even then they like to spin at 3500 Shaft RPM plus.. To me, they are just a “bill of goods” and sell strictly on max amp out out, which BTW is intermittent duty at best..

You need a Delco 24SI or 28SI unit.. 3X the output at 1500 shaft RPM with is about where you are at engine idle.

Tony

[Jon Fitch]

Hmm, tried to post a reply but it won’t let me. The alternator is a Balmar 94-12-210-IG. I’ve spent the money but if another could be found with similar specs but higher low speed output (that will fit!) I’d consider it. The engine draw exceeds the output by itself, so the DC architecture of the boat is irrelevant.

According to the published Cummins specs, a number of the 6BT and 6BTA engines idle at 700 or 750.

What’s the magic of the 600 rpm idle? The engine idles smoother a little faster, in my boat and others. I normally throttle up a little with the transmission locked out for that reason, but it isn’t practical to do when maneuvering.

[Corey Schmidt]

What EXACT alternator do you have now? Let’s chase this problem down from the other direction. The exact model & specs along with your current DC distribution architecture will help us “help you”…

The comments are correct, you need to source an alternator that can “keep up” at the standard 600 RPM. All Cummins mid-range elec/mech engines idle at 600 RPM. No reason to mitigate a problem by raising the engine idle, rather it is best practice to mitigate the issue by either sourcing the root cause or replacing the equipment to suit the demand, etc.

A Cummins technician should technically be able to plug in to the engine ECM and raise the idle value, although I doubt they’d do it without some heavy resistance.

[Scott Lambert]

Idle RPM

My understanding, limited as it is, is that the idle speed is controlled by a voltage signal from the throttle system. So if you have a Glendinning throttle system you would need to make a change there. As far as I am aware this is not possible, but Corey may know a bit more? Otherwise you could try Glendinning? For the record my QSB 5.9 idles at 600 rpm and alternator output is fine.

[Jon Fitch]

It is a Balmar 94 series alternator and Balmar 614 regulator. I could find no other alternator that would fit the space available without very substantial modifications. It should be noted that Cummins requires an offset pulley with limits the choices somewhat.

[Scotth]

Sorry this is being difficult for you on the idle side. I have not worked with an electronic Cummins, only mechanical Cummins or newer Volvo/Deere.

What alternator do you have now? Internal or external regulator (what type)? I used to work in a marine electrical store, might be additional setup options.

[Philip]

Then you might be left to install a different alternator or an externally adjustable regulator.

[Jon Fitch]

Thanks for the suggestions, but everything has been checked, all works as it is supposed to. A larger pulley will overspeed the alternator at full rpm. I just want to change the idle and I am astonished at how hard this is proving to be.

[Scotth]

Sorry, no help on your idle issue.

Can you install a smaller pulley on the alternator?

[Philip]

Have you load tested your batteries? Often times that can be the issue.

Notice I didn’t ask how old your batteries were as it not uncommon for a battery issue to manifest itself this way no matter the age.

Phil

[Jon Fitch]

Nothing wrong with the alternator. It is a large frame high output and they put out less at idle. Since a 6BTA engine idles at 700 I don’t think I’ll have any more trouble than they do.

I’m pretty amazed at how hard it has been to find out the answer to this seemly simple question.

[dave carey]

Alternator

Just thinking, maybe the alternator is giving up? It should be able to produce enough amps at 600 rpm. Also, if you set to 675, it will be more difficult to do low speed docking.

[Author]

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