Can the idle speed on a Cummins QSB be changed?

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
DDW said:
I was hoping someone had some information on the original question.
Click to expand...


I think your only hope is to get a Cummins tech who know how to adjust the idle and can come do it. Between travel etc., it will probably cost $1000, so worth considering in the context of other solutions.


You could also give Glendinning a call. They may have some magic too. Both ZF/Mathers and Twin Disc EC300 controls have provisions for a programmable fast idle. But I'm not sure about Glendinning. I last had their controls in conjunctions with QSC engines, and had no need for fast idle because the alternator kept up just fine at 600 rpm idle.
 
twistedtree said:
Can you pull the actual alternator part number off the unit? It's probably a Leece Neville/Prestolite. From there you can find the actual data sheet which will give you max rpm. I would expect 8000 rpm or more. At least that's what I've found for large frame units that I've used.
Click to expand...

The Balmar isn't a rebranded something else, they do build them themselves. Now the frame, rotor metal, and bearings are all some standard thing, I'll agree. I'm told the limit is the bearings, seems to be a needle roller in back and a deep groove ball in front. In any case I'd have thought increasing the idle speed would be easier than making a custom K8 pulley but perhaps not.

twistedtree said:
I think your only hope is to get a Cummins tech who know how to adjust the idle and can come do it. Between travel etc., it will probably cost $1000, so worth considering in the context of other solutions.
Click to expand...
Fortunately the boat is currently about 100 ft from a Cummins technician so they could stroll over, do it, stroll back and have all of 15 minutes in the exercise. But they don't know how to, have a call into Cummins, no answer after a couple of days. Maybe Cummins doesn't even know?
 
DDW said:
Mine is set to the standard 600. Alternator does not put out enough at that speed to keep up. .
Click to expand...

Why is this an issue? As suggested, can you not just advance the throttle?
 
Last edited:
sunchaser said:
Why is this an issue? As suggested, can you not just advance the throttle?
Click to expand...

It's the alarms on both the ECU and some other system. Sitting at a dock, sure, idle up a bit with the throttle.

Maneuvering: shift forward, shift neutral, shift reverse, blip the throttle, back to idle, ALARM ALARM, shift forward, cancel alarm, shift nuetral, ALARM ALARM

Etc... False alarms are a bad thing. They train the user to ignore them and cause undue stress during normal operations. Those suggesting 'just advance the throttle' aren't listening to the OP's issue.
 
sbman;765993. False alarms are a bad thing. They train the user to ignore them and cause undue stress during normal operations. Those suggesting 'just advance the throttle' aren't listening to the OP's issue.[/QUOTE said:
SB
Your likely correct. His initial post does not use the word alarm, but the story indeed gets deeper. Unknown to any, does 675 ease the alarm bells? If not, what RPM does?

As suggested by TT, likely an alternator issue. DDW says no. I've another thought DDW. How are your house and starter bank isolated from one another? A sufficiently charged up isolated starter battery should be able to provide a sufficient voltage buffer.

There is likely something else going on here than a factory set RPM, just have to find it.
Click to expand...
 
Does the alternator feed both the start and house batteries through a battery isolator? If so the voltage drop through the isolator may be enough to trigger a low voltage alarm? Just a thought, if this is the case, replacing the isolator with an automatic charging relay could fix the issue.
 
Correct on the maneuvering. This is an electronic throttle, to increase the idle without it in gear, one must push the lockout button and advance the throttle. Then back to idle position, push the lockout button again, shift for a burst, back to idle, push the lockout button, advance to increase idle. It isn't practical when maneuvering. I've done it for a couple of days, it is prone to error and distraction.

The alarms go off at around 12.4V. The net draw is around 5 or 10 amps depending on what's running. A fully charged starter battery is 12.7V. Doesn't take long to pull it down to 12.4 with that draw. Try disconnecting your alternator and you will see this. The starter battery isn't new and perhaps a new battery would help, but that is covering up the problem. The house is isolated by a combining relay, this does not turn at as the voltage is below the charging set point.

There was no problem with the stock Delco alternator, except that it did not charge the house battery adequately. The switch to this alternator is what created the problem. Everything is working exactly in spec - its just that this particular operating point doesn't work well.
 
I'm surprised you get alarms at 12.5V That's a well charged battery.


I wonder if you have some significant voltage drop between the battery and the engine ECU?
 
Could be? Decent sized cable for the amperage, the Smartview display indicates about 0.1 less than the battery monitor. This I believe is measured in the ECU. 12.3 isn't really that low, but (I think) they believe it should be charging and they should be seeing 13+ and they aren't, so it alarms. Which it probably should do normally speaking. The alarm is to inform you that the alternator is not charging, and it isn't. There is a bit of a delay before you get the alarm, so it isn't panicked - just concerned. The throttle actually has redundant supplies, one from the start and one from the house battery. But again, with no charge source, both are below charge (and normal running) voltage.

I did finally talk to someone at Cummins who said Insite on most engines will set the low idle, but it may depend on the software revision level and engine. Said the option may be greyed out in some situations, so may just have to try it.
 
DDW said:
There was no problem with the stock Delco alternator, except that it did not charge the house battery adequately. The switch to this alternator is what created the problem.
Click to expand...

Why not put the Delco back on and rethink how best to charge your house bank to suit your needs?

As previously suggested, change some sheaves maybe. Do you have the space for two alternators? All said, the new alternator isn't performing in its present state.
 
Once again, this is the only high output alternator that will fit on this engine. It is performing exactly as the output chart says. The pulley ratio already overspeeds it. There is no way to fit two alternators on a QSB without major fabrication and changes.

The Delco alternator did a crap job of charging. Supposed to be 95 A but as with most automotive alternators, rarely got more than 40 out of it and voltages set too low. I can't think of a better way to charge the house batteries than a proper alternator on an already running engine that has around 300 extra horsepower to burn.

All will be fine when I bump the idle speed up 75 rpm.
 
MG 540 and 5600 are 750 rpm max for engagement and it was the TD dealer/tech who told me told me that the harsh engagement wasn’t good and to keep the idle speed down.
 
DDW said:
I'm not raising it for charging. It is specifically while maneuvering at idle that this is a problem. I'm happy to lock out the shift and bump the throttle up any other time. It is not practical to do that maneuvering with the Glendinning control.

I'm surprised everyone thinks this is death to a Twin Disc. The mechanically injected predecessor to this engine (6BTA) is set to idle at 700 from the factory, and was typically fitted with the same transmission, probably 10s of thousands of installs. Sure slower is always better but these transmissions will not roll over and die at 700 rpm idle.
Click to expand...
I believe 6bta's usually idle at 600rpm. Some folks adjust mechanically to 660 for smoothness.
 
DDW said:
The question is, how long can you run at max rpm before the alternator blows up? It is spec'd as 6000 rpm max (they have told me 6500 is safe), max on the Cummins is 3050 or 8500 on the alternator. Max realistic cruise is 2500, 7000 on the alternator, still above the spec, if I go to 3:1 then 7500. And won't get the same effect as increasing the idle to 675. Do I want to be worried about the alternator when running at max cruise? Also, I'd probably have to make the pulley - can be done but a bit of effort. The Cummins pulley is not the same as other engines.

The alternator is externally regulated (MC-614), and the sense wire is on the start battery which is feeding the engine electronics. The regulator shows 100% output but cannot achieve the target voltage.

Setting the idle up seems like the simplest solution.
Click to expand...
If using MC614 regs you can fit alt temp sensors and program the reg to de rate the alt when it gets too hot...and you get to decide what that temp limit is (ask the alternator manufacturer obviously)
 
on the alternator not charging enough at idle, which is the speed we troll at, i went from a 4 inch pully, to a much smaller one! voila, now it`s in the 15/20 amps...keeps the house batts up fine! several yrs ago, i took my external regulatr off, and bought a new leece/nevile 165 amp, [new design] it never goes over 14.1 volts, so the batts don`t use water...clyde
 
QSB idle

I too have a Cummins QSB (5.9) that came with a 125A Delco alternator and it was not a great performer at our typical engine speed of 12 to 1400 rpm. Our start battery, a 4D Lifeline was just that, starting only. All other power for the engine, electronics, etc. came from a 440 Ahr house bank. Our typical output (net) from this alternator was always positive at idle and our load was around 40A with radar, radio, Furuno BBMFD, and a 24” Apple Cinema Display for our screen all powered up. We subsequently changed the alternator for a Delco 250 amp, externally regulated, alternator designed for bus application, i.e. low engine rpm and high loads at idle. We noted significant improvement in low speed and idle charging and have had no issues running at WOT with the right sensors and belt management settings.

To pull your battery voltage down from fully charged to 12.4V (approx 50% discharged) in a short time indicates to me that you may well have a battery issue or charging system issue. Assuming your worst case draw of 10A and a 200 Ahr battery you should be able to idle for many hours before reaching 12.4 V ... definitely more than 6 hrs. A simple load test should be able to pinpoint if the battery is the issue
 
senojev...were you writting to me, clyde, about your charging system, or to all the forum? i was talking about running slow, and when trolling at idle, or slower, to keep the batts up! a friends was bad, he had to run the genset when anchored...clyde
 
The 1000 rpm shift limit is directly from the TD manual, I quoted it verbatim above.

Many 6BT and 6BTA engines are spec'd to idle at 700 and 750 rpm. Some 600. There is no magic in the 600 number. You can look up all these specs on the SBMar site.

The MC614 I have already has the temp sensors installed. This is not a hot vs. cold issue.

An LA battery at 12.4V is down somewhat - but that is an at rest, no discharge number (Lifeline suggests 4 hours rest before test). Put 10 or 15 A discharge on it and it will pull down some. The battery is not new, it starts the engine with no trouble at all but I have not tested it for load or capacity. Since it is serviceable (it starts the engine) the system ought to work with it. Don't want to have to have a brand new battery all the time to have it work. The warnings are intended to indicate that the alternator is not charging, and that is in fact the case. I do not know what the trip point for them is, but it appears to be between 12.7 or 12.9 volts. Above that, no warnings. So a full new battery may not be the answer anyway.

That said, what model of Delco alternator did you put on? Where can I find specs? Nothing like that is listed in the Delco/Ramy catalog.
 
Last edited:
Here is an illustration of the problem: high output alternators put out less at low rpm. This is the same Delco 28SI alternator in 3 different specs, chart is from Delco. This is the highest output alternator that Delco currently lists (that is not pad mounted). On the QSB, alternator is turning 1600 rpm at 600 rpm engine idle. There is a HUGE difference in output at 1600 rpm between them (and note that these are cold ratings, hot will be about 2/3). At 1400 shaft rpm the 200A puts out zero. Eventually the 200 A version passes the others. This is typical of high output alternators. The modern exception is the AT style hairpin wound alternators which put out very good current at low rpm. They will not work on the Cummins without substantial fabrication, if then.

Now bump the idle to 700 and the alternator shaft speed to 1900: very similar output, problem solved.

MfvOfM9.jpg
 
Have you had any progress finding someone that has the ability to modify the idle speed? Makes me appreciate my mechanical detroits!
 
Yes actually. A couple of calls to Cummins tech support and they said it can be done with their Insite software with rare exceptions. I've scheduled it with South Island in Sidney, who are a Cummins rep, are about 100 feet from the boat, and are willing to try. I'm going to do it in the water so I can try shifting a few times and see if the engagement is too abrupt. I doubt it as the earlier 6BTA boats seemed to shift fine, but it would be good to tune that while the tech is still there and plugged into the ECU.

At the time this engine was built, you could get a "C-Cruise" option, a rocker switch on the dash that would allow you to change the low idle at will (up to something like 800). Tried to find those bits on the secondary market but no joy. The electronic engine is up several levels of complexity. The electronic throttle isn't just a potentiometer or voltage source like the days of old, it is a CAN bus node, communicating on a digital link to the engine. There is no hot wiring of these things like in the past. The C-Cruise option likewise.
 
What sort of boat is the motor in? I don't think you've mentioned it. Is the Cummins original or a repower?
 
It is an American Tug 34, the installation is original and unchanged, other than the upgrade alternator I just installed.
 
DDW
Two years ago I noted South Island dropping two new Cummins 6.7s into an older boat, it went well.

Also, Delta up the road has a terrific engine guy. Good luck.
 
DDW said:
Here is an illustration of the problem: high output alternators put out less at low rpm. This is the same Delco 28SI alternator in 3 different specs, chart is from Delco. This is the highest output alternator that Delco currently lists (that is not pad mounted). On the QSB, alternator is turning 1600 rpm at 600 rpm engine idle. There is a HUGE difference in output at 1600 rpm between them (and note that these are cold ratings, hot will be about 2/3). At 1400 shaft rpm the 200A puts out zero. Eventually the 200 A version passes the others. This is typical of high output alternators. The modern exception is the AT style hairpin wound alternators which put out very good current at low rpm. They will not work on the Cummins without substantial fabrication, if then.

Now bump the idle to 700 and the alternator shaft speed to 1900: very similar output, problem solved.

MfvOfM9.jpg
Click to expand...


The datasheet that that chart comes from also lists the max continuous RPM as 10,000, and intermittent as 12,000. So you could change to a 3.3:1 ratio to get about 10,000 rpm at WOT, and just under 2000 rpm at idle. I'm not sure where the 6000 rpm limit came from.
 
That is a Delco alternator, not the Balmar that I fitted. As I said, Balmar limit came directly from Balmar. This Delco is only a convenient example of the difference in curves which is typical. On this one, I could fit a smaller pulley, but it is internally regulated, has the wrong mount style, and is too large to fit the space available.
 
I mentioned the Balmer alternator temperature sensor in an earlier post because I was assuming a strong relationship between the alt's shaft speed and temperature.... but perhaps this is not the case?
 
DDW said:
That is a Delco alternator, not the Balmar that I fitted. As I said, Balmar limit came directly from Balmar. This Delco is only a convenient example of the difference in curves which is typical. On this one, I could fit a smaller pulley, but it is internally regulated, has the wrong mount style, and is too large to fit the space available.
Click to expand...


OK. But in my experience, the Balmar alternators are nothing more than re-badged Delco or Prestolite alternators. Maybe this case is an exception to that.
 
Delhi Alternator

DDW

I stand corrected. My upgraded alternator was not 250 A as stated in my response but a 200A 28 QSI. The specs for this show a max RPM continuous of 10,000 rpm and 12,000 RPM intermittent.

The output graph shows that at 600 rpm engine speed and with a pulley ratio of 2.8, the output should be around 82A. This is way higher than you are achieving from your alternator which I believe is a Balmar 94. Note that the published Balmar output data is based on a 2:1 pulley ratio. Using your 2.8:1 ratio, you should be seeing around 35A.at idle. To me it appears you have an alternator/regulator problem.
 

Attachments

  • 5766414C-C422-4203-B2BA-A75D99C6E7C4.jpg
    5766414C-C422-4203-B2BA-A75D99C6E7C4.jpg
    76.4 KB · Views: 44
twistedtree said:
OK. But in my experience, the Balmar alternators are nothing more than re-badged Delco or Prestolite alternators. Maybe this case is an exception to that.
Click to expand...

Every Balmar I've had has not been a rebadged anything. Sure the cases and rotor steel are from something, maybe a Delco or Prestolite, but everything else inside is quite different. Certainly this one is. Diode plate, bearings, windings, fan, etc.

Published data on the Balmar 94-12-210-IG is here, in table form. Output at 1500 shaft rpm when warm is 15A. I'm running about 1680 rpm. Also that is one example in the lab, not sure what the expected variation is but I'm getting about what the spec says. The field current from the 614 is slightly under the spec, I will look into that more.

Where did your Delco 28 come from? Delco does not list an externally regulated alternator in their catalog, and the 28 will not fit on my QSB without quite a lot of modification. How did you get it bolted up? Not sure what output graph you are looking at - that competitive comparison one does not match the other one in the same literature. 80 A isn't achieved until 2000 shaft rpm - about the same as the Balmar.

All of these alternators have very steep curves in the low rpm region, a few rpm makes a big difference. That seems like the easiest solution to me.
 
You must log in or register to reply here.

Similar threads

O C Diver
My John Deere decided to take some time off
2 3 4
Replies
119
Views
11K
dannc
D
markbarendt
Mix or Match on the boat's bum?
Replies
5
Views
681
tiltrider1
tiltrider1
Portage_Bay
An interesting read on the security of GPS
2
Replies
40
Views
3K
AMG
A
mncruiser
Dinghy power results (with a surprise twist!)
Replies
14
Views
4K
Dougcole
Dougcole
Miz Trom
Lost Steering on the Tennessee River - Facepalm
Replies
20
Views
7K
cardude01
cardude01

Latest posts

Back
Top Bottom