Motorola Model 12SA115

[Dualfuel]

Alrighty,
I did some homework (read the white paper) and decided its time to start this project. I have had this Motorola for years and just haven't found the engine I like to belt this up to.
The white paper makes sense. The problem is, I don't have a 24volt bank, and am unlikely at this time to recapitalize my infrastructure to use 24volt. So...I will run the 12SA in its 12volt form.

Its been my experience, when hooking a Delco 10SI to a big battery bank, that the 10SI will give its all. My original set up had a 2hp horizontal shaft Briggs and Stratton engine hooked to a 37amp 10SI. Attaching the jumper clip to a dead battery or a big battery bank would stall the engine. So....14.7volts times 37amps is only 543 watts, which, even with belt drive, should have been low enough that the 1500watt engine could drive it. Turns out a 10hp Tecumseh Snowblower engine was the only one with enough chutspa to not stall when a 37 through 80 amp 10SI were giving full output. From this I suspect that these alternators will give much more then they are rated at. My question for Bob is: what size engine should I belt up to this Motorola?
Should I expect similar behavior from the motorola?
The Motorola should put out at least 1764 watts according to the data plate, how much more could I expect?
I am worried that all I have to turn this thing is a 22hp Wisconsin badged Lambordini diesel. I don't care for this monster at all. Pinging through that aluminum block can be heard even if one is in the next township.
I have a crazy idea: I have a like new 12 or 14hp Briggs and Stratton riding lawn mower engine....its electric start (which is a MUST HAVE feature). I could do the long twisted belt thing, to go from vertical shaft to the horizontal orientation of the alternator.
In this cold weather, its 13F right now, I tend towards spark ignition. Gasoline engines are usually easier to start when its this cold. Two strokes being the easiest.
I have a few 8hp horizontal shaft engines to work with but at 5968 watts, if there is that over charging capability in the Motorola, I would think it would need some kind of current limiting method to keep it from stalling the engine.
Anyhow, thats what I have so far....


(BTW, the way to not have the delcotron destroy itself, is to not use the 10SI but the older externally regulated delcotron, and instead of having a regulator, just hook up an old sealed beam head light between the positive and the field terminal. The head light acts as a resistor and limites the output to something like 12.8volts. You can try different head lights and get the voltage you need, but remember the higher the voltage the harder that little devil will try to charge. So I let it go for a while at 12.8 til the bank is up then I hook up the regulator, and go up to 14.7 from there.)


yours BPJ

[Ronmar]

Well you have obviously encountered the drawback of a standard automotive regulator.  They will give all the alternator has to give and more in trying to fill the hole of a discharged battery.  Without current monitoring, you have no way of knowing how much the alternator is actually trying to output into the batteries.  Rule of thumb for 12V alternators is 30A of output per engine HP, or 435W per HP.  This is pretty close to, but a little more conservative than, the standard of 2HP per KW.  If your 2HP engine was operating at rated RPM to deliver a full 2HP, you probably pulled in excess of 60A, but without an ammeter, you will never know.

One of the problems with using an alternator with the standard regulator, is that you need to use an engine large enough to drive the alternator at it's absolute maximum possible output.  If it is a large battery bank, the alternator will burn up trying to fill the hole running at it's absolute maximum output for extended periods.  Or as the bank charges, you are now driving an alternator running at reduced output with a way oversized engine.  Alternators with the automotive regulator are designed to top off relatively small starting batteries and power the vehicles loads.  They do this very well.  To better use an automotive alternator for large bank charging, you really need a programmable regulator to 1. Control and limit the alternators output to stay within safe long term operating/output limits. 2. Stay within the available HP of the chosen engine.  In this way, the regulator can match the alternator to the engine, and allow sustained operation at an efficiently/best utilized engine HP output.  The regulator can also more effectively charge the batteries by following a 3 or 4 step charge plan that helps to prolong battery life...

So for a long term charger, you use an alternator capable of say 75-80A maximum and spin it at an RPM to reliably deliver that output and move enough air to stay cool.  You connect it to a 2HP engine running at the RPM required to deliver that full 2 HP.  Then you use a programmable regulator/controller that limits the alternator output to no more than 60A.  The engine dosn't get overloaded.  The alternator dosn't burn up.  The engine runs at an efficient loading for most of a charging run... 

Since battery bank charging efficiency falls off as you approach full charge, Ideally you would have a larger generator for the large current bulk charge, so it can run at an efficient engine load.  Then you have a very small generator, like the 2HP unit I just described, to be used for the finish charge portion, so it's small engine can be run at an efficient load...

My .02 

[SteveU.]

Hey BrucePJ
I'll let Mobile Bob handle the required small engine power needed for your large frame Motoerla - he has the on hands experience with that.
I have however repaired/rebuild a few hunderd of these off of truck, industrial and marine applications. This is a good heavy solid efficient unit electrically.  But . . . as originally made with the single spool foot mounting off of the front frame only as you have they had a nasty tendency on big diesel engines to snap off and shake loose the thru-bolts letting the ass end sag and then rotor drag. 1st thicker heatreated bolts -> then the thru-bolt sleeve 'n nuts reinforcements picture you show on one visible -> then finnaly Motorla had us hacksaw shortening the spool from 3" to 2" and adding a 1" wide sliding sleeved bushed foot bracket hanging down frome the lower two thru-bolts to directly support the rear case assembly. New factory from then on they just cast in a rear housing foot to begin with.
SO normal horizontal mounted watch your viberation mounting isolation if driven by a shaking single cylinder.

Bearing life of vertical remounting any nornal horizontal alternator will vary by the alternator and bearings designs.
This would be a good on to do as a double ball bearing unit. The front bearing as I recall is a 6205-2rs. These are available in a semi-axial thrust configuration. Full axial would probably fail due to the belt side load.
Ha! Ha! My memory is just unreliable enough you'd best tear down and verify the installed number before ordering a bearing. Maybe actually a 6305-2rs?
Verically installed the whole rear housing support concern wouldn't be a problem then.

Regards
Steve Unruh

[Dualfuel]

Thanks Ron for the idea about dual engines. That is not an absurd thought when it involves me as I have lots of engines. Yes to everything you have described. I have a 4kw Yanmar that is belted to 10SIs and for the last six years it has steadily destroyed them or the belts. The 10SIs give their best then suddenly the smoke clears and the Yanmar's RPM goes up. Its then I know to go and put another one on. With daily charging of the big bank the Yanmar will kill a 10SI in about three months, though some have lasted as long as a year.
Hey Steve,
I weighed that 12SA and its a 30lber! Its not going to be a trivial mounting job with some plumber's straping and a bungy cord. Right . Tnow I am trying very hard to remember where on this property I saw an engine with a double "A" belt pulley. The thing that keeps coming to mind was the "Mr. Goodwrench" engine in my 1970 C50. If thats the case then I guess the generator would be portable (more shoveling to find out).

One thing I just remebered is that in the back of a suburban out there, I have a golfcart engine, a Kohler with the variable clutch and the starter generator. If the shaft isn't tapered, perhaps I could replace the clutch with a double "A" belt pulley and have a good combo.

Now folks, I dearly love effciency. But what I am building here has nothing to do with that. If I am running some engine that is sucking down a gallon an hour, its because I have to. In the months between October and April, conditions for machines here, go from benign to actively hostile. Only the toughest things will run right now, like the steel snow shovels, splitting mauls with the steel pipe handles, and engines like the Waukesha in the loader. I suspect the Kohler or the B&S  would start well if the oil was thin, and once started my gratitude to have it running overwhelms my despair at the lack of fuel effciency. I am not whining, but an explaination seems inorder.
Presently, we live pretty close to the earth. No problem, as this is my earth and I proudly own it, outright, with taxes paid. So with no shelter for machinery, what I do have running by this time of year is pretty rugged stuff. That Honda eu3000i, is one of those rugged machines, sitting outside on a foot stool, with a plastic dog kennel over it. This upcoming construction season we will build a house for the honda and a CHP plant for the IH engine, but right now its pretty hand to mouth.
This is kind of funny, but to give you a better idea of how it goes sometimes, I had four chrysler minivans parked in a half circle around the battery bank and I would use them to charge the batteries. Which ever one started that day, I would use to charge the bank. Then that spring, I sold them for scrap and bought my first batch of solar panels, and didn't start an engine for three months. Feast or famine, anything to keep that drip coffee pot going.
Ya, I'll keep strolling around memory lane here to see if have anything that would be Motorola ready...meanwhile its off to paint the basement.
BPJ

[mobile_bob]

if  you are limited to a 12volt nominal battery bank, i would figure no more than
75% of nameplate amp rating out of that alternator for continuous duty use.

so if it is a 120amp unit figure on limiting to about 90amps

where the increase in capacity comes from is when you repurpose it to charge at 24volts or higher, the same limit of 90amps will net you twice the effective power in watts and generally higher efficiency.

in my experience most folks figure around 25amps per hp delivered from an aircooled gas engine. Ronmar's suggest 30amps per hp, so figure somewhere in the 25-30amps per hp as being within reason.

you would do better with a 24volt bank in my opinion, that is in efficiency.

bob g

[vdubnut62]

Hey!  With my little eye I spy a Maytag hiding behind that Motorola!
Ron.

[Dualfuel]

Good Eye! Its the only hit and miss engine I own. Dragged it out to weigh for a fellow who wanted to know how much shipping would be....
BPJ