Can the idle speed on a Cummins QSB be changed?

[Senojev]

Delton 28

The Delco 28 I have was bought for $285 from a Delco dealer on the east coast. I had it converted to external regulation at a local alternator shop for $75. It has around 1000 hours on it with no issues. I don’t understand why this would not fit on your Cummins QSB as I think this is the same engine as in my 37 Nordic. The Delco is offered in several standard mounting configurations. Installation took about 30 minutes. Just a matter of removing existing Delco and bolting in the new one.

The curves I provided come straight from the Delco brochure. It provides 120 A at 2000 shaft rpm or just over 700 engine rpm with a 2.8 pulley.

In your response you note that you believe your Balmar output matches their published data. That would be true if you have a 2:1 ratio but you stated you have a 2.8 ratio. With this ratio, you should be getting around 35/40A at your idle speed so the alternator is not meeting spec and I would suggest returning it. For the price of the Balmar you could buy 4 of the 28 QSI.

 

[DDW]

I am aware of the difference in ratio. I am going by alternator shaft rpm. I am also quoting hot figures, which are quite a bit lower than cold - the Delco curves are cold. I posted the brochure curves above - there are two in the Delco 28, and they do not match: one shows competitive analysis (the one you posted) and the other shows a comparison of their different 28 specs (the one I posted). They are significantly different at the low end. Which is correct? One shows 120A @ 2000, the other about 80A @ 2000. Hard to read them anyway since the line thickness covers several hundred rpm. The Balmar specs are tabular, and shows 15A @ 1500 shaft rpm, 68 A @ 2000 shaft rpm.

I'll look into the 28 more. In the current catalog, Delco only shows a J180 mount which might fit the later QSB. I have the 2" foot. It can be changed by fabricating a new mount or purchasing the changed out parts from Cummin$ which will cost more than the alternator. My QSB also has the remote oil filter, the lines of which tightly wrap the alternator, interfering with anything even slightly larger than the original 19SI. The dimensions shown in the Delco literature suggest it will be about an inch too big in both directions. I am told this might be removed which would leave a little more room.

Yes, Balmar has never been accused of being underpriced.

 

[twistedtree]

This thread shows there are a number of paths to fix this problem, each with it's own costs and trade-offs. You are focused on increasing the idle, which is as good an approach as any.


I just find it odd that the Balmar, which is designed specifically for marine use, would not have a usable RPM range. With their 6000 rpm limit and a 3000 rpm engine, that means 1200 rpm at idle, no charge, and alarms. And if you "gear" it to provide even a modest charge at idle (what you are pursuing), then you are over-reved at WOT. And plenty of engines rev even higher than your QSB's 3000 rpm, so the problem only gets worse. If nothing else, I wonder why their rpm limit is so much lower than other similar alternators like the Delco which is also available in a 2" mount with the same output rating.

 

[DDW]

I wonder those things too. This particular Balmar has about the lowest output at this shaft rpm of anything they sell. From this thread and another on the SBMar site, I'm beginning to think the Delco 28 would be a better choice. Preliminary research shows I need to swap the alternator mounts to the J180 version, not available in Cummins distribution, I've got them checking at the factory now. Can always machine one, but it is difficult with the boat 800 miles from my machine shop.

I got into this corner by trying to make the fewest changes, so that I could keep the Delco 19si alternator as a viable backup. Any of the other schemes involves changing over to a J180 mount, making regression more difficult. Also, it had not occurred to me, nor did I research, removing the equipment that is in the way of other choices, namely the remote oil filter which in this installation actually makes it less, rather than more accessible.

 

[Northern Spy]

I wonder if it has something to do with the alternator's field drive settings at idle. If it is programmed to delay or "soft start" on a ramp every time the speed decreases to engine idle. Or if it is even flashing the field at all at low revs.

Assuming this is externally regulated; is there a setting in the regulator that you can change? Presumably this would be there to protect the drive belt and minimize parasitic load.

 

[DDW]

I've measured the field current when it's idling and causing the problem. It is at 100% according to the regulator (which does display this information) and I've measure it at 5 amps. It's a K8 belt on a 380 HP engine, no reason to protect anything.

I'll say it one last time, the alternator is producing what it's data sheet says it should. Does not happen to be enough for this application.

 

[Northern Spy]

I've measured the field current when it's idling and causing the problem. It is at 100% according to the regulator (which does display this information) and I've measure it at 5 amps. It's a K8 belt on a 380 HP engine, no reason to protect anything.

I'll say it one last time, the alternator is producing what it's data sheet says it should. Does not happen to be enough for this application.

My apologies. I reread the thread with a more critical eye.
I see that you had already answered my speculation.

 

[DDW]

It looks like the 28si might fit, if I source the J180 mounts and remove the remote oil filter mount. Senojev must have a later QSB engine, these came with J180 mounts and some different piping for the oil filter. The J180 mounts are not available in Cummins distribution, but couple of calls to the Cummins factory confirm that they do have them and I can special order them. Removing the oil lines should give enough room for the short hinge J180 version of the 28si. Also opens up the possibility of several other J180 mount alternators. I'll consider the $1200 Balmar sunk cost....

 

[Ski in NC]

You may be able to ditch the remote filter and move the oil filter to the adapter where the lines attach. I'm not 100% this can be done, but I think some of these blocks the filter goes right on the block. Also depends on the boat whether this is a good idea.

 

[DDW]

Yes it appears that the remote filter mounts on the normal filter mount in place of the filter, so the whole mess can be removed and the filter reinstalled in its normal location. I'm not sure why the remote was specified for this boat, it is more accessible in the normal location, and the leaks drip into the drip pan instead of onto the alternator when you change.

I'm told to expect a few psi increase in oil pressure as well.

 

[FF]

Then there is always Plan B

Back in the day the sailors faced dead batts ( mostly from refrigeration),as engine drive with eutetic was expensive .

The" T Mac " was a solution . The std voltage regulator would be switched OFF ad a variable resistor was used to lower the boats voltage to what ever field current was needed to charge a Delco car alt at about 1/2 its rating .

Worked well IF the sailor could touch the batts to keep from overheating them near the 85% full point.

A PIA to operate , but lots cheaper with car parts store Caddy rebuilt alts.

And it worked!

 

[DDW]

A last note: I changed the alternator to a Delco 28si modified to external regulation, and swapped the mounts to J180. It does just barely fit without other modification. The shop that did the external reg conversion ran a curve on it. The Balmar 94 was putting out about 20 A at 1600 shaft rpm (which is my 600 rpm engine idle). That is about what their curve says (tabular data 15A @ 1500). The Delco according to test is 115A @ 1600 rpm. Kind of a big difference. I put it in and fired the engine and at 600 rpm idle the charge voltage limited at 14.5V and 63A. So, problem was with the Balmar alternator, just not enough umph at low speed, as I thought.

Thanks to those that encouraged looking at alternatives, I'll be happier with this solutions. Not to mention, Balmar is $1200, Delco was $220 + $150 to modify.

 

[clyde]

DDW...the person i deal with concerning alternators and charging, and starters, is a good friend, and alternators/starters are his business, introduced me to the latest gtreatest LEECE NEVEL 160 amp alternator, never goes over 14.1 volts, which means the batts use very little water! when i`m troling, not many amps were being made, so i decreased the size of the pully as far as i could, which solved the problem! i have a nice $400 ample power external reg, for sale @$100, but most people at our yat club are not very up on these things! i have 6, 265 amp 6v/means 3 265 amp 12v house, and 2 grp 31`s in paralel, for 1500 amps for starting my volvo 70B!...clyde

 

[DDW]

If you are just charging a flooded start battery, the 14.1 volts is OK (actually a bit high). If you are charging a house battery, particularly an AGM one, an external 3 stage regulator is essential, unless you want slow charging and quick battery failure. 14.1 is too low for a fast charge, and too high for float charging. Internal regulators are designed and built to recharge a flooded starting battery, they do that well, but are poor at charging house batteries on a live aboard boat.

 

[twistedtree]

Glad you got this sorted out, and ended up with a good solution.