The International Cessna^® 170 Association

In the 170, the amp meter indicates the rate at which the battery is charging or discharging, it does not indicate the total output of the generator. The value shown on the amp meter should be less than the total rated output of the generator.

The regulator amp adjustment is for the generator output and not the charging rate of the battery. If you adjust the value to produce a 25 amp charging current for the battery you could overload and fail the generator and possibly the regulator.

Thank you N1277D. It is all becoming clear, almost. First Eric, the battery is old and was severally drained. I new this and that accounts for the 15 or so amps charge rate when no other load is turned on. And why when additional load was added the rate went down. I will probably be buying a new battery shortly.

But my last question still remains. How do you go about adjusting the regulator to make sure it's adjusted right to gain the rated amperage of the generator. In this case it is 25 amps.

Seems if the battery was charging at a rate of 15 amps according to the amp meter. Then I added and additional 5 amps of load. The amp meter should have stayed at 15 amps if the regulator was adjusted correctly according to N1277d. It didn't but dropped buy the mount of the additonal load. In this case it would seem the regulator was adjusted to limit the output of the generator to just 15 amps.

Bruce, the "correct" way to adjust your regulator is to send it to Aeroelectric, (I usually recommend AeroTech in Louisville,) or whoever you like to use, and have it calibrated on the bench.
The "shade tree" way to do it (which most of us prefer) is to do it at home ourselves.
When your ammeter is used, you should realize it's not a calibrated
gauge and may be off considerably. But if you wish to use it, here's how.

Firstly, the ammeter doesn't measure output from the gen. It measures input into the battery. If your battery needs 30A over a 2 hour period, but you only have a 25A gen/reg system, then it'll show 25A (assuming no other device is turned on) for something longer than 2 hours before it tapers down. (That's not exactly the case, but it's an illustration that works in this instance. Otherwise I'd have to get into amp/hour rates etc., and this forum is too limited for that treatise. Come to the convention seminar.)
But, keep in mind that the ammeter is only telling you the relative amount of charging rate your battery is accepting. That equals the EXCESS amount your gen/reg can generate that your other accy's aren't using.

So, with no accessories on, the positive reading on the amp gauge is the battery charging rate. (Sounds like your system is currently regulated down to a maximum of 15A output capability, IF your battery is healthy. If your bat is damaged, it may request a continual charge even tho' it's not storing it. Such condition will skew this method of testing/adjustment....you're back to sending the unit out.)
With a healthy 25A charging system, adding accessories to that should act like this: Adding a 5 A load will not affect the 15 A batt charge rate you've been seeing because the 15A bat-chg rate, plus 5A load still only equals 20A. Adding another 5A load also will not affect the 15A chg rate you originally saw because you are now only asking for your gen's max 25A capability. Adding another 5 A load will drop your ammeter's indication to 10A bat chg rate because you're now asking for 30A from a 25A system, and that last 5A accy is stealing pwr from any excess gernerated capability available for battery charging. In other words, the generator will attempt to supply al accy's with pwr FIRST...and any left-over capability will go to the battery....IF....IF...it needs any recharging. This is why the aircraft's ammeter is such a lousy test-bench to adjust a regulator. You really have no idea of the needs of your battery until it is fully charged, and the ammeter drops completely off to Zero. (And a damaged battery may never let it do that.)
Adjusting a regulator requires adjusting the screws that manage spring tensions (or on cheaper regulators actually bending the tabs the springs hang onto). The seminar will address these methods at Tehachipi.
If you can get a fully discharged battery, get the engine propped to start it, and turn the system on with NO accys on, then you should see 25A charge rate from your 25A system. Anything less than that, with a completely discharged but otherwise healthy battery (no shorts, no damaged plates, etc.) means the regulator isn't asking for full output from the generator. Caution: It's possible to adjust a regulator to request too much from a generator. Do that for long and you'll be buying another generator. That's why it's OK to use a 20 A reg on a 35A gen, but not a 35 A reg on a 20A gen.
BTW,...with regards to indicated voltages....as the system starts charging a discharged battery the voltage reading should be about 12.4 V or slightly more. AS the batt begins to fill up the voltage will climb up to 13.2-14.2 Volts. At this time the ammeter should be indicating only a few amps positive. When the Ammeter reads zero, the voltage should hover around 13.6 or so. If you see more than 14.5 your regulator is allowing too much/unnecessary voltage rise and your battery will need frequent servicing of water.
Hope this helped.

Yes George, between 1277D and your post I understand whats going.
I've got another questin for you.
A friend (electrical engineer) says that the regulator really only has a high and low charge setting. ie the field fully grounded or field grounded through a resistance depending on whether the coil is energized and has the points closed or not. Is he right?
I'm thinking the points will vibrate allowing for a variable between the 2 extremes. The harder the spring is pulled the less the points will vibrate and more amperage will be allowed to the max the generator can make. The trick is to adjust it to just less than the rated amperage of te generator.

BTW I plan to be at your seminar George. I just hope I still don't need any help by then

Your electrical engineer friend is technically correct, but as you've already noted, the voltage regulator actually has points that vibrate at high frequency thereby averaging out the actual requirements for voltage and current. It is the vibrating points that sometimes causes electrical interference with older radio equipment, and why a large condenser in the Armature (never the field) circuit will dampen the sparks and electrical noise (and also prolong the life of the regulator.)
The old vibrating points regulators are archaic designs but purists like them. The newer solid-state regulators avoid all the mechanical points and their frailties/limitations, and that's why they can design them to make generators behave somewhat better.
Keep in mind that alternators and generators both do the same thing,...they take mechanical motion and magnetism to induce a current in the wires. The alternator converts the AC (alternating current) to DC (direct current) that the battery can store by using solid state check valves called diodes. The generator does the same thing but does it mechanically by switching the current direction of flow at the commutator/brush interface. Since the amount of time spent mechanically swithing that current is by necessity a longer time-frame...the generator needs more rpm to make useful quantities of rectified AC current. The solid state components of the alternator do not require the necessary time to mechanize the activity, and that is the basis/primary advancement of alternators over generators. (But if I were to admire that advancement...then similar logic would also call for turbine power in my 170. I like the 170 because it's a classic....not because it's solid-state advanced. The only reason my 1939 9N Ford tractor has a 12V alternator instead of it's original 6V generator is because someone had already thrown all the original stuff away.)