Alternator Curves

[edwardc]

Has anyone come across a set of output curves for the Mando (now API) 55 Amp alternator that MMI sells showing output vs RPM and temperature? I've spent some time digging on the web, and found the manual, but haven't been able to turn up a set of curves yet.

[ndutton]

Ed,
This graph is for the Arco 60050 which is listed on the API site as the same as their 55A as well as the Mando. What ratio are you using to calculate alternator RPM (necessary for the graph to be meaningful)?

[Dave Neptune]

How much?

Neil, would the regulator not have a lot to do with RPM vs output? Or is the graph just the "capability of the alt" itself?

Dave Neptune

[ndutton]

The graph presents alternator amperage capacity while a regulator controls the output voltage. Tweaking the output voltage up on manually adjustable regulators* would result in higher amperage output (still within the limits of the graph) but at the risk of high voltage system damage at some point. Our EI ignition system seems to be one of the more sensitive due to massive dwell and its effect on the coil.

*note that the only adjustment available on manually adjustable regulators is voltage because that's all they regulate.

Further comment on the pulley ratio:
The standard Motorola 35A alternator spins at 1.75x engine RPM. However, my Delco 10Si spins at 1.5x. It's important to measure the pulley diameters (drive and alternator) and calculate your own ratio (drive diameter / alt diameter) before using the graph.

Since Ed brought this up I studied the output curve for my alternator and it revealed something quite interesting. When I bought the alternator it was sold as a 100A Delco 10Si. As part of a necessary internal regulator replacement to tame down the voltage I had it dyno tested. At 2000 RPM (alternator) the output measured a little over 50 amps. Studying the graphs for various Delco alternators, the highest 10Si shown is a 72 amp model and its output at 2000 RPM is only 22 amps while the 12Si 94 amp model is right at 50 amps according to its graph. Since both the 10Si and 12Si are the same physical size and appearance I'm calling mine a 12Si from now on based on measured performance and published data. Applying the pulley ratio discussed above to the 12Si 94A graph, I can expect up to approximately 72 amps output at 2000 engine RPM. Of course I'd have to be abusing my batteries to ever reach that output.

[hanleyclifford]

The graph in post #2 is very instructive. Most of the available amperage of both alternators kicks in around 4000 rpm. If you cruise around 2000 engine rpm, the 2:1 ratio will set you up nicely.

[hanleyclifford]

As Neil has correctly pointed out, the regulator regulates voltage; amperage is based on what the batteries are calling for. The problem I have run into with steep ratios, alternator to engine, is the load on the engine at start up (before the engine reaches operating temperature) can be substantial and makes me uncomfortable, which is why I abandoned 3:1 and went to 2:1. If someone could come up with a way to delay full amperage output until the engine is warmed up I would consider going back to the 3:1.

[BadaBing]

Assuming an alternator is installed, as mine is, how would I go about measuring the actual amp. output of the alternator? I had my alt made for me by a local alternator shop. The owner/mechanic/wizard knew our atomic 4 engines, the limits on revs and existing drive pulley size. I was asking for 100 amps, which he said was almost impossible to do, partly because of heat generation by the alt itself. He told me he would "take care of my need", then charging my 2 - 4D batteries and powering up my inverter to run the electric water heater. What ever he built it seems to be doing a fine job, I just refer to it as a 100 amp out of habit. I do not run an amp meter, partly because the original was to small and partly because it the location of the gauges would more than double distance and resistance of the charging wire- from alt. to meter - battery switch / battery.

My inverter constantly displays my voltage, which serves to keep me updated on the voltage output of the alt.

It would be nice to be able to know what amperage I am putting out at set RPMS. Just for the sake of knowing. Is this something I could test with an amp meter from alt to ground?

Thanks

[ndutton]

With a shunt type ammeter distance is not a factor. Here's one that will suit your needs. It installs in the alternator output wire.

http://www.ebay.com/itm/like/331612885593?lpid=82&chn=ps&ul_noapp=true

Do not be alarmed if the reading seems low. Alternator output is determined by the connected battery's State of Charge so unless the battery is dead flat the alternator will probably not be operating at full capacity.

[romantic comedy]

Hanley, does not the regulator control the field of the alternator. You can switch the wire that goes from the regulator to stop the alternator from charging. At least that is the way I understand it.

On my battery select switch there is "field disconnect" terminals. The purpose is to break the field and stop the charging while changing batteries in order to prevent damage to the alternator.

I have a Balmer ARS III regulator. It is made to delay the alternator from charging for a short time. It is about 30 seconds to a minute. I can here when the alternator kicks in after start.

I have been threatening to add a field switch for 15 years. This way I could let the engine warm a bit.

[hanleyclifford]

Hanley, does not the regulator control the field of the alternator. You can switch the wire that goes from the regulator to stop the alternator from charging. At least that is the way I understand it.

On my battery select switch there is "field disconnect" terminals. The purpose is to break the field and stop the charging while changing batteries in order to prevent damage to the alternator.

I have a Balmer ARS III regulator. It is made to delay the alternator from charging for a short time. It is about 30 seconds to a minute. I can here when the alternator kicks in after start.

I have been threatening to add a field switch for 15 years. This way I could let the engine warm a bit.

Yes, the regulator senses voltage and based on what it "sees", it delivers current to the field. At one time I did have a manual "controller" with various resistors and three switches in the event of a voltage regulator failure. Later I used it as a "composite" resistor in the ignition circuit. Problem was it was manual and cannot be used with a regulator. Your regulator with the "delay" is probably the best solution.

[romantic comedy]

Hanley, why not just have a switch? on/off. You could even have a timer. After running the batteries down, there is quite a load on the engine. Not something I like to do to a cold engine.

Wish I could program that regulator to hold off for 5 minutes.

[ndutton]

Wish I could program that regulator to hold off for 5 minutes.

Easy to do with a delay-on-make relay such as McMaster-Carr 77055K736. You realize you'll be running off battery power only during the warm up period.

[romantic comedy]

I guess if it started on battery, 5 more minutes wont make a difference. Thanks Neil.

[ndutton]

I use the same timer (different timing range though) on my alarm system and it has performed flawlessly for years. I can't stand buzzer noise on startup like all those smelly diesels. From ignition on to arming my alarm is 10 seconds.

[hanleyclifford]

Hanley, why not just have a switch? on/off. You could even have a timer. After running the batteries down, there is quite a load on the engine. Not something I like to do to a cold engine.

Wish I could program that regulator to hold off for 5 minutes.

I had a look at that delay switch Neil recommended, and I like the idea of a delay. However, that only solves part of the problem; the other part is the sudden enormous output at switch-on. I would also like to increase amp output in stages after warm up and that might be complicated.