Slant Six Forum :: newer alt in a 63 Valiant

Wait a second.

All the current doesn't go through the ammeter?

Wait a second.

All the current doesn't go through the ammeter?
Only a relatively low current line parallel to the main current path?

p.s. No adjusting screw on the 157B

The new voltage regulator and new wiring work!
I haven't re-attached the speedo cable yet and the instrument panel could be easily removed.
I like the diode shunt solution. Can you give me some more information?
What part number do you recommend for the silicon rectifier diode?

You know that short red wire from the bulkhead connector's ammeter return terminal to the starter relay's big terminal?
Would replacing that with a 14ga fusible link be a good idea or bad?

Quote:

I wanna see the info too. The more people pestering 440_Magnum, who is an Electrical Engineer, maybe the more likely he is to cough it up!

Author:	SlantSixDan [ Sat Sep 10, 2005 6:55 am ]
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I figured the 157B was probably points type. I'm guessing no external voltage adjust screw? Pity. That was a nice feature of the original ones of those. '70-up regulators work well. Running 10ga wire as you describe is certainly not a bad idea. I don't think I'd eliminate the factory wires, I'd run the new wires in addition. There's plenty of room on the ammeter's connection studs, and that way you maximise your current capacity through this area.

Author:	mcnoople [ Sat Sep 10, 2005 9:32 am ]
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How much energy will a stock ammeter take before a meltdown? Does anyone know what the design spec was? I've pegged mine out when charging up a dead battery and the 80 amp (according to the sheet supplied with it) alternator didn't hurt it as far as I can tell. The only wiring upgrades I ever did to it beyond dual field/flat pack is audio junk.

Author:	Pierre [ Sat Sep 10, 2005 9:55 am ]
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The ammeter can take the current, its the wiring thats the questionable part. The one in my 71 duster is labeld -40 to 40, I think some were -60 to 60. If you look on the back of the ameter, theres a solid metal bar connecting the two studs together, and then a small piece that extends out to interact with the pointer mechanism. Pegging the meter won't ruin its ability to conduct. It may distort the accuracy of its readings and damage the pointer itself, but the car electrical system will still function fine.

Author:	SlantSixDan [ Sat Sep 10, 2005 12:10 pm ]
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And if you're really concerned about what might happen when you're giving a jump start or after you've had one, you can always put in a bypass on the firewall that temporarily shunts past the ammeter when you throw it.

Author:	sixsignet [ Sat Sep 10, 2005 12:49 pm ]
Post subject:
Wait a second. All the current doesn't go through the ammeter? Only a relatively low current line parallel to the main current path? p.s. No adjusting screw on the 157B

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Author:	SlantSixDan [ Sat Sep 10, 2005 1:17 pm ]
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Quote: Wait a second. All the current doesn't go through the ammeter? All ammeters are really milliammeters. A shunt is used (either internal or external, it's internal in this case) to match the current loads to the ammeter. Imagine the size the whole thing would have to be if it were directly measuring currents on the order of tens of amps! You've got a 2" gauge there, so there's only room for very small wire windings and a very small gauge movement. So, yeah, most of the current runs through the shunt. I haven't done enough recent examination of the factory ammeters to determine how easy/difficult it might be to add shunt capacity such that the gauge would still indicate but would not peg when upgrading to a higher-amp alternator.

Author:	skraecken [ Sat Sep 10, 2005 1:44 pm ]
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I have got a Bosch 70 amp generator, and no problem with the ammeter.

Author:	sixsignet [ Sat Sep 10, 2005 1:54 pm ]
Post subject:	never mind
Is there an article somewhere (with diagrams) that deals with upgrading from the old to the new regulator? As I understand it, one of the two FLD wires from the VR has to get +12V from the wire that was connected to the top terminal of the old alternator never mind. I found one. Here it is: http://www.imperialclub.com/Repair/Elec ... arging.htm

Author:	SlantSixDan [ Sat Sep 10, 2005 3:08 pm ]
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The two FLD terminals on the back of the new alternator are interchangeable. It doesn't matter which field wire goes to which terminal. One field terminal needs to see +12v via a newly-added wire whenever the ignition is switched on. The other field terminal simply gets the existing field wire, which runs to the regulator.

Author:	440_Magnum [ Sun Sep 11, 2005 12:19 pm ]
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Quote: Wait a second. All the current doesn't go through the ammeter? Only a relatively low current line parallel to the main current path? p.s. No adjusting screw on the 157B It depends on the year of your Mopar. From the 60s through somewhere around '77 or thereabouts, Mopars did use ammeters that took the WHOLE charging current. If you crack one open, you find that its "field coil" is just a single turn of relatively heavy brass conductor. After the 70s, they went to the more reliable shunt method, where the ammeter in the dash is actually a milliameter and a shunt wire carries the bulk of the current. The early ammeters will certainly burn out if subjected to a huge current, but to be perfectly honest I've run 100A alternators on two cars ('66 Polara and '73 Satellite) with full-current ammeters, and haven't popped either one. Normally, a healthy battery simply will not accept a charging current greater than 30 amps or so because it builds up voltage fairly quickly. A dead but otherwise healthy battery may absorb between 10 and 30 amps for a LONG time before it is fully charged, but it won't suck down a full 100 amps. The exception is offering a jumpstart with your engine running. In that case, a pretty big slug of current will go through the ammeter- up to the full alternator output. I see two possible solutions: 1) install a heavy-current ammeter bypass switch and heavy wiring, throw it whenever you're offering a jump. 2) Install a permanent shunt bypass with an in-line silicon rectifier diode in the forward-bias direction. The diode won't conduct until the voltage across the existing ammeter and wiring is 0.7 volts, which should be enough to let the ammeter work... up to a point... but not overload.

Author:	sixsignet [ Sun Sep 11, 2005 7:17 pm ]
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The new voltage regulator and new wiring work! I haven't re-attached the speedo cable yet and the instrument panel could be easily removed. I like the diode shunt solution. Can you give me some more information? What part number do you recommend for the silicon rectifier diode? You know that short red wire from the bulkhead connector's ammeter return terminal to the starter relay's big terminal? Would replacing that with a 14ga fusible link be a good idea or bad? The rest of this circuit is now 10 ga.

Author:	SlantSixDan [ Sun Sep 11, 2005 8:32 pm ]
Post subject:
Quote: The new voltage regulator and new wiring work! I haven't re-attached the speedo cable yet and the instrument panel could be easily removed. I like the diode shunt solution. Can you give me some more information? What part number do you recommend for the silicon rectifier diode? I wanna see the info too. The more people pestering 440_Magnum, who is an Electrical Engineer, maybe the more likely he is to cough it up! Quote: You know that short red wire from the bulkhead connector's ammeter return terminal to the starter relay's big terminal? Would replacing that with a 14ga fusible link be a good idea or bad? Generally, fuselinks are sized four gauges smaller than the circuit they're protecting. So, the right gauge fuselink for a 10ga circuit is (12, 14, 16,) 18 gauge. H'm. Maybe not the best way to protect the circuit. The rest of this circuit is now 10 ga.[/quote]

Author:	sixsignet [ Sun Sep 11, 2005 8:42 pm ]
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Before I started it up the first time, I ran a couple of wires from the battery to a voltmeter. I was pretty nervous. It is actually charging a little at idle! This is 700 rpm. The ammeter is slightly to the right, but the voltmeter reads 13.5 volts! The battery was 12.8 at rest. I just found out that a standard 12 inch metal ruler exactly matches the two slots on the starter switch ring.

Author:	440_Magnum [ Mon Sep 12, 2005 9:54 am ]
Post subject:
Quote: Quote: The new voltage regulator and new wiring work! I haven't re-attached the speedo cable yet and the instrument panel could be easily removed. I like the diode shunt solution. Can you give me some more information? What part number do you recommend for the silicon rectifier diode? I wanna see the info too. The more people pestering 440_Magnum, who is an Electrical Engineer, maybe the more likely he is to cough it up! Or maybe he'll just get grumpy. :-p I hesitate to recommend too much just because I haven't yet tried it and tweaked things. In theory, what you'd need (and like I said, I really SHOULD do this myself!) is a silicon rectifier diode capable of carrying 100A or more (steady state or average current, not just a surge current). Mount it on a good heat sink, and wire it in series with a wire from the alternator "bat" terminal to the battery. Put it in so that forward bias is current flowing from the alternator to the battery. Wire with good heavy-guage wire (10 ga or better). That way, the existing ammeter carries all the charge current UP TO the point that there's about 0.7 volts drop across it due to its internal resistance. That should be many amps of current. At that point, the shunt with its diode begins to conduct and carry all the additional current. If 0.7v still leaves too much current going thru the stock ammeter (I don't think it will- seems like I've measured over a volt of drop during heavy charging) then you could use a GaAs diode or a Schottky diode. But my guess is that the Schottky diode would shunt so much current away from the ammeter that the ammeter wouldn't indicate anymore. <google google> Big silicon rectifier diodes: http://www.alldatasheet.com/view.jsp?Searchword=UR1 Another option would be to just use a bank of alternator diodes and wire them in parallel. Not pretty, and you'd have to make sure everything is insulated, but it might be a good option.

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Author:	sixsignet [ Mon Sep 12, 2005 10:33 pm ]
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Wouldn't a single diode mounted across the ammeter terminals do the same thing? All the related wiring has been upgraded to 10 ga or better.