Alternator Always Charging

The correct generator/alternator voltage for a wet cell vehicle battery is 7.15V, +or- 0.05V. This was the factory set point for generator regulators that came after the A era. Most old repair manuals for all generator era cars call for adjusting cleaned and repaired mechanical regulators to that range.

All of the aftermarket one-wire alternator regulators are set for an extremely high 7.5 or (gasp) higher output. This is done for several reasons:

 1) The assumption is a car that is driven once a week or less, maybe for an hour, with a battery that has sat and discharged somewhat, and likely less than perfect electrical connections. You get an extremely high charge rate and fast recovery within that single hour of drive time.

Disadvantage: If all your connections are excellent, you drive more than an hour a week, and you start with a fully charged battery you are instantly boiling/outgassing/overcharging/damaging your battery. Think about it- 7.5V on a 6V battery is the same as a whopping too-high 15.0V on a later 12V battery.

2) The bean-counters victory.- "Wow, my lights sure are bright with the new alternator!"
Yep, that 7.5V+ set-point sells 'em fast.

Disadvantage: A bulb marked 6-8V that lasts 300 hours on 6V lasts maybe 50 on 8V. @7.5V, maybe 75 hours. Try 15V on your 12V modern wheels and see how many bulbs you go through!

Unfortunately there are NO correct 7.15V regulators for the popular 10/12SI one-wire alternators. Additionally those repop regulators have no soft-start. Instead they deliver a whopping (to my oscilloscope and your vehicle electronics) start up square edged surge. There is also no time or temperature compensation to adjust and taper the set point as the vehicle runs and warms under-hood, and the inital starting discharge is recovered. Modern alternators do these things, but not antique 10SI's with one wire conversions.

It is possible to open up a Transpo 6V one-wire 10SI regulator and change the internal voltage-divider resistor array that controls the rotor current drive transistor to give you a more realistic 7.1V set-point, but that is not a do-it-yourself job for the average car enthusiast.
 
Ruth said:
Not sure I agree with that. When I turn on my lights I definitely see an "influence" on my ammeter.
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You see the drain from the battery that the generator is not providing. I could have worded that better, I suppose.

Turn up the generator for night driving to keep the battery charged.
 
To MikeK's point - optimum battery charge voltage is 7.2 -7.9 volts for a 6V battery, twice that for 12V (14.4 - 15.8). Most regulators are set near the midpoint, 7.4 & 14.8, for fast charging with no boilout.
 
Badpuppy said:
To MikeK's point - optimum battery charge voltage is 7.2 -7.9 volts for a 6V battery, twice that for 12V (14.4 - 15.8). Most regulators are set near the midpoint, 7.4 & 14.8, for fast charging with no boilout.
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I would respectfully disagree with that completely. The voltage ranges you spec apply to independent external chargers, not factory spec mechanical generator regulators or integrated regulation multi-wire alternators as originally factory installed.

If left on for extended time or frequently applied to an already fully charged battery those charger set points you list WILL take their toll on a battery.

The regulators set with set-points you list are one-wire jobs or cheap replacements that lack temperature and time compensation that will reduce the initial set voltage significantly, generally in less than 20 minutes of operation. Those replacement aftermarket regulators also lose or lack the ability to remotely sense voltage, usually at a major junction point far from the device output terminal.
 
Thanks for the info, Mike. But I'm not aware of any time/temperature circuits in any automotive regulators I've seen. The original GM 10Si, for example, has a single set point, a remote sense terminal and an ignition terminal. A steady charge voltage conducts less current as battery charge builds up, so there should be no reason to change it over time.
 
Alternators on cruising sail boats put out more than 65 amps. They are controlled by sophisticated charge controllers (regulator). They have a complicated charge cycle as shown below. They also have a temperature sensor that is attached to one terminal of the battery to adjust the charge voltage.
 

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nkaminar said:
Alternators on cruising sail boats put out more than 65 amps. They are controlled by sophisticated charge controllers (regulator). They have a complicated charge cycle as shown below. They also have a temperature sensor that is attached to one terminal of the battery to adjust the charge voltage.
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Thanks for that. Looks similar to modern battery tenders. But I've never seen anything like that on a car. Maybe too modern for me. Learn something new every day.
 
From what I remember of old Delco internal regulators there was nothing fancy about them.
I'm still thinking the issue is a bad regulator. It could have easily/cheaply been changed awhile ago. Then we'd know if it fixed it or not. I don't know if his alternator would have the 'D' slot for full fielding or not. Some early ones didn't.

Some of these threads certainly take on an interesting life of their own.
 
MikeK has a point about these types of 1-wire conversion alternator. On the GM/Delco 10si type alternators, the rectifier is changed to get the 6-volts needed and has a jumper to the regulator module and the brush holder stack. These alternators may be one wire now but they were never designed to be that. They have the plug with the 2-male spade terminals that were used in the original OEM installations for the alternator warning light and the system voltage sense. Model As and tractors don't use this stuff but that doesn't mean that they couldn't. It's just that it is not considered important by the producers of this equipment. If these two circuits were set up (making it a 3-wire system), it may help with the output of these type units. That voltage sense wire was pretty important to the way the internal regulator works. Since the regulator doesn't know what the battery voltage is, it just has to put out a constant default voltage for it to work.

The alternator has to be pulled apart and a conversion regulator set up purchased to supply the parts for replacement but it can be done by most DIY guys.
 
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nkaminar said:
Alternators on cruising sail boats put out more than 65 amps. They are controlled by sophisticated charge controllers (regulator). They have a complicated charge cycle as shown below. They also have a temperature sensor that is attached to one terminal of the battery to adjust the charge voltage.
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The light dawns. That charge rate is appropriate to Li-ion batteries. Lead acids are not so finicky. I stand by what I said before.

What powers the alternator on a sailboat?
 
On our sailboat the alternator was on the main engine, a Diesel. Most sailboats are set up that way. We had two huge deep discharge house batteries and a large starting battery. All were flooded lead-acid batteries. The engine was run for an hour once a day to charge up the holding tanks for the refrigerator and freezer. We had solar panels so the alternator was not needed unless the house batteries were run down because of using the inverter or other big loads. The charging curve is designed to charge the lead-acid batteries in the shortest amount of time and to their full capacity. This was years before Li-ion batteries were available. The charge controller for the solar panels had the same charge curve.

The holding tanks for the refrigerator and freezer contained a salt solution that froze and then melted throughout the day to maintain the proper temperatures.

On a sailboat the engine is used to enter an anchorage or to get to a dock at a marina. It is also used to motor when there is no wind or when trying to head directly into the eye of the wind. We motored about half the time. I hated to do it but it was necessary.
 
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katy said:
I assume that you meant regulator, not rectifier?
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I meant rectifier. Here is a link to a kit on flea-pay.
https://www.ebay.com/itm/10SI-Delco...r-Rebuild-Conversion-Kit-/190696606664?_ul=IN

The kit includes the regulator and brush holder stack with special hardware and the rectifier bridge block. All of this stuff makes for a positive ground polarity, 6-volt alternator. There are even U-tube instructions for these conversions.

It's one way to freshen up an older unit as well since it comes with bearings too.

The best way to use a 10/12si type alternator is as it was originally intended. That is 12-volt 3-wire system but most folks don't want to go 12-volt or negative ground.
 
nkaminar said:
On our sailboat the alternator was on the main engine, a Diesel. Most sailboats are set up that way. We had two huge deep discharge house batteries and a large starting battery. All were flooded lead-acid batteries. The engine was run for an hour once a day to charge up the holding tanks for the refrigerator and freezer. We had solar panels so the alternator was not needed unless the house batteries were run down because of using the inverter or other big loads. The charging curve is designed to charge the lead-acid batteries in the shortest amount of time and to their full capacity. This was years before Li-ion batteries were available. The charge controller for the solar panels had the same charge curve.

The holding tanks for the refrigerator and freezer contained a salt solution that froze and then melted throughout the day to maintain the proper temperatures.

On a sailboat the engine is used to enter an anchorage or to get to a dock at a marina. It is also used to motor when there is no wind or when trying to head directly into the eye of the wind. We motored about half the time. I hated to do it but it was necessary.
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OK, I get the picture now, thanks. Pretty elaborate, but apparently more reliable system. Hard to wrench it while standing on the side of the ocean.

Come to learn Model A, learn to be a sailor instead. I'm an inland boy; stays out of the water.
 
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