85 hp Chrysler overcharging battery

[fifty2one]

I'm having a really perplexing charging problem with my 85 hp Chrysler. The model number is 857HA, which makes it an old one- maybe 1969 or so. It has a selenium rectifier and step regulator. I discovered after the Magnapower ignition died that the battery was being routinely charged to 15.5-16V. I replaced both the rectifier (#85450), and the regulator (#A321470) with NOS parts (like still in their original boxes), and saw absolutely no improvement. At idle, the voltage climbs towards 16V over a period of several minutes. The battery is one year old and it is an Interstate HD24-DP (flooded design), 405 CCA, with about 70Ah capacity.

Here is one other clue: before I replaced the rectifier and regulator, I noticed that about 5-10 minutes into very run, the tachometer rpm's would fall off to values that didn't make sense. The tach sense wire is connected to one of the yellow terminals on the rectifier. I checked the stator when the motor was cold, and found 1.1 ohms between the wires, and no continuity between either wire and ground.

Is it possible to have a good battery, rectifier, and regulator but still have the system overcharge battery? Could a faulty stator alone cause the issue? Could you tell me how a step regulator works? Thanks, this really has me baffled!

 

[gm280]

:welcome: to iboats fifty2one. Nice for you to join us...

I personally can't see a stator working perfect until it gets hot and then outputting more voltage/current. That truly goes against everything electrical in my book. I mean a stator is nothing more then some wires wrapped around a metal base. So how can getting hot make it output more voltage... :noidea: That would mean the windings would have to be increased in numbers to provide higher voltage/current. So I will say no, it can't be a stator issue from what you posted. And have you actually used another meter to verify the voltage your are reading. I realize meters can give suspect readings and make things look questionable. So verify the meter with another one to see. However, all that stated, if the output from your engine is charging at a higher voltage, it isn't like it is running for hours on end. So I don't see much problems with a little higher charging voltage then usual either. If you already replaced the two functioning parts that do control the charging capability and there is zero difference, then I wouldn't worry about it. Others will chime in with their recommendations I'm sure. JMHO!

 

[Nordin]

The stator will produce higher voltage when the RPM rise and on that old rectifire/regulatorsystem the charging voltage will reach 16-18VDC.
The regulator on this old system is just a simple zenerdiod with a zenervoltage about 16-18VDC. The zenerdiod is connected to the rectifire + plus terminal and the other side to ground.
When the voltage reach about 16-18VDC the zenerdiod starts to "open" and then it lead the stator voltage to ground.
SO att high RPM when the charging voltage reach 16-18VDC the zenerdiod cut out the voltage to ground.

Newer regulators work in another way with newer typ of electronic components .

 

[fifty2one]

Thank you both for your prompt responses. I knew I would find the right expertise here!

I have to agree, it just seemed crazy that a faulty stator would overcharge the battery - it should discharge it.

What you both said about the higher voltages, puts things in an entirely different light. If the step regulator switches in the 16-18V range, then my ignition probably just died from old age rather than overvoltage. The Magnapower I system must have been designed to tolerate those voltages. I had been going on the assumption that 16V was excessive for the electronics (and it might be for later systems).

So it sounds like things are working as they should, but the tach weirdness might be suggesting that my stator is having some intermittent problems.

 

[Jiggz]

My tach intermittently does the same thing and so far I cannot find any reason the problem is from the stator. This is after installing a secondary tach, Tinytach, which seems to be steady. Instead, with the tach being almost 30 yrs old, I presumed it is the caused of the problem. When it goes haywire a simple tap fixes it back.

 

[fifty2one]

That's very interesting....I hadn't thought about the tach. It's an Airguide and had been working fine before the Magnapower ignition died. Magnapower parts being scarce, I had to convert to an automotive coil. The tach had been sensing rpm's at the CD box, but with that gone, I had to change the jumper wiring on the back of the tach and move the sense wire to the alternator. So maybe it is the tach. It's never been used in alternator configuration before.

Now that I know that the normal system voltage is 16-18V, I wonder if my automotive coil will survive. It does seem to get awfully hot.

 

[Nordin]

As you says the tach is reading from the Motorola CD box and it suppose to count ign.pulses from the box and in this case three pulses each engine revulotions.
When you convert to Automotive ign.system and connect the tach to the stator/alternator.........yes it will not read right because the stator signal is a 2 phase sinusvave signal.

 

[Frank Acampora]

Most auto coils are designed to run on 9 volts. This is because when the engine is cranked to start, battery voltage drops to about 9, yet starting is when you absolutely want maximum spark.. Thus the coil is designed to run at the minimum voltage expected. There is a special circuit that bypasses a resistor at start and includes the resistor at run. If you want full life from your coil, you should consider inserting a resistor in series with it.

 

[fifty2one]

That is a very good point about the coil, Frank. I'm using the NAPA coil with a built-in resistor that others have used for this purpose. Do you think since I'm operating in the 16V range that some additional resistance would be warranted to keep the primary coil current in check? Or, would it make more sense to switch to a later regulator/rectifier combination that would limit to a lower voltage range?