Stock alternator upgrade question

[Hank Dodge]

I've still got the stock 40amp alternator in my rig. I'm thinking that I'd like to upgrade it if possible to something higher while still retaining my existing wiring and amp gauge etc. My truck is still pretty much original wiring etc. and it's still in good serviceable condition, so I'd like to keep it at this point. Is there a good upgrade to something like a 60 or 70 amp alternator that you folks could recommend? Would I need to upsize the regulator as well?

Thanks

 

[Steve83]

There's absolutely no advantage (or use) to the stock ammeter, and the wire it uses can't handle double the current. Its loop won't accept a much-larger wire. So either stay below 60A, or do a worthwhile upgrade to a 130A 3G and lose the ammeter - or at least its function. You can leave it in-place as a filler, but a voltmeter will be far more informative than the best ammeter.

If you keep an old-style (1G) alternator, you can keep the original voltage regulator.

 

[OX1]

You could go to a larger case 1g alt, which were 70 amps min I believe, but I don't see the point over a 3G. 3G is easier to wire, eliminating ext reg (as mentioned).
I'm not sure if the large case will even fit where the stock alt goes on an EB, it is substantially bigger.

 

[DirtDonk]

He's already stated though, that he wants to keep his ammeter.

And yes, the larger case fits with very little fuss. Just a couple of connectors changed, and possibly a longer belt, and away you go. I had to elongate the slotted hole on the lower bracket by about 1/4" to let the belt I bought fit, but many others have done it without that particular mod.

And I still disagree with Steve on the relative merits of a working ammeter and the carrying capacity of the stock wire. I think that, AS LONG AS THE WIRE AND CONNECTORS ARE IN GOOD CONDITION, it can handle 70 amps.
Certainly 60, which is a very typical output for the small case 1G these days. I think the original was more in the 45 amp range, which is picking nits of course, but unless yours is original Hank, it's probably even a 55 or 60 by now.

Is it original?

Paul

 

[BwoncoHowie]

You could go to a larger case 1g alt, which were 70 amps min I believe, but I don't see the point over a 3G. 3G is easier to wire, eliminating ext reg (as mentioned).
I'm not sure if the large case will even fit where the stock alt goes on an EB, it is substantially bigger.

I made the large case 100A swap, and even with a large pulley to slow it down, my headlights will not dim @ idle even with the wipers, and heater blower on high. I did this primarily to power my H-4 Halogens. Here is a tech article I prepared just for mounting the unit. http://classicbroncos.com/tech/alternator-mounting By clicking on the photos you can enlarge them.

I built a wire adapter that made this swap to be plug-N-play with no cutting and splicing of the original harness.

 

[broncnaz]

A lot of mid 70's vehicles with A/C had 65 amp small case alternators. Your local parts store should have them just check the stamping on the case it should have the AMP rating stamped into it. I agree with dirtdonk most alternators will now be 65 amp anyway.
Voltage regulators are all basically the same although early regulators had points in them and were a taller more square setup. later regulators are solid state and flater and more rectangular So basically there is no regulator upgrade to speak of other than soild state over old pints type.
Even if you went to the big 90 amp alt unless you have a lot of electical equipment running all at once you should never see a 90 amp draw but even so just upgrade the main batt wire from the lat to the solenoid.
The Ampmeter in EB's only measures the differance in battery output and alternator output full power doesnt actually run through the ampmeter or its wiring its only measures current differances by means of a loop in which the wire runs through. theres no actual connection of the wire to the ampmeter. The wiring to the ampmeter is not the main circuit wire. itsd just a loop to provide measurement.
Lastly there are kits availible to upgrade small case alternators to 80 or 105 amp but they tend to be kinda pricey $50-60.

 

[OX1]

The Ampmeter in EB's only measures the differance in battery output and alternator output full power doesnt actually run through the ampmeter or its wiring its only measures current differances by means of a loop in which the wire runs through.

I know the 78/79's were this way and suspected the EB's were also.

 

[OX1]

I made the large case 100A swap, and even with a large pulley to slow it down, my headlights will not dim @ idle even with the wipers, and heater blower on high. I did this primarily to power my H-4 Halogens. Here is a tech article I prepared just for mounting the unit. http://classicbroncos.com/tech/alternator-mounting By clicking on the photos you can enlarge them.

I built a wire adapter that made this swap to be plug-N-play with no cutting and splicing of the original harness.

I have several large cases left over from parting out older F250/350's over the years, but have never run across a 100 amp large case (at least not installed in anything I parted).

Seems they are 150$ everywhere I look for remans. Got a good source for them in the yards and or anywhere to get a killer deal on a reman? I eventually want to use it for an on board welder in my new rig.

For years I held off going 3G, but I finally made the swap about 8 years ago. Really was no comparison to the stock 70 amp large case. I did just grab 4, 3G's from a yard recently for 120$. JY one in my 79 has lasted 8 years so far.

 

[Steve83]

The Ampmeter in EB's only measures the differance in battery output and alternator output...

It measures what's going into & out of the battery, except the starter load. It has nothing to do with the alternator.

...full power doesnt actually run through the ampmeter or its wiring ... The wiring to the ampmeter is not the main circuit wire..

When the engine is off, every bit of current used in the truck passes thru that wire, except the starter. When the engine is running, only the charging current passes thru it, until the alternator's capacity is exceeded; then the battery begins supplying the deficit. The ammeter wire is the only connection from the battery to the alternator & truck (except the starter), so it's about as "main" as you can get.

I'm not sure about '78-79, but '80-86 use a shunted ammeter, which is really just a voltmeter across a resistor wire, so it doesn't have full current to the meter. Later trucks use a plain voltmeter.

 

[broncnaz]

Ok lets go this route a fairly stock bronco system only pulls so many amps just upgrading the alternator doesnt mean you will put out 100 amps. Now you add on accessories you dont normally wiring them into the stock wiring they go direct to the battery so you have not increased any load through the amp meter wiring. While it may show that you are charging over the 60 amps it can show. The full amperage is not running through the ampmeter wire thats why its looped into the main charge wire the main charge wire will handle the main load the ampmeter wire only measures whats happening. Now if your main charge wire is to small for the amount of power going through it than yes power will try to flow through the ampmeter wire.

 

[Hank Dodge]

Thanks for the input. Looks like the best thing for me at this point would be one of the 60amp small case units. That would give me a little more than what I've got now anyway and I wouldn't have to modify a thing. I'm not running much over stock as far as electrical load goes, just a few extra lights and an inverter for 110v power tools from time to time. I do like the idea of the large case 100amp unit being able to supply more load at idle speeds though.

Just thinking, is there any room to go with a smaller pulley on the small case alternator and have it start charging at a lower RPM without a problem? I know my 40amp unit does not really kick in until I get above idle speeds. I'd assume that the 60amp unit would be the same way. What do you think?

 

[Steve83]

...its looped into the main charge wire...

It's not looped anywhere. It's the only connection from the battery & starter to the alternator & the rest of the vehicle, so it IS the main (& only) charging wire. So if you add anything to the dash wiring or fuse block, it pulls thru the ammeter wire when the engine is off. Adding stuff at the battery allows it to draw directly from the battery, but it ADDS to the load thru the ammeter wire when the engine's running because it can pull the alternator's max output.

So we were both wrong. %) The stock ammeter wire isn't looped & IS the main charging wire, BUT: it doesn't need to be upgraded immediately with every 3G swap. If there are no new loads, then the only load thru the original ammeter wire is the battery charging load, which is the same as before, and should never go over 60A.

Here's a simplified (& corrected) diagram showing the 2 arrangements:



But if there IS an extra load at the battery (at the frowny, like a winch, amplifier, inverter...), then the original ammeter wire has to be upgraded to handle the entire alternator output (with some safety margin) since it could conceivably carry that much when the engine is running. If the new loads are attached at the fuse block (the smiley), the stock ammeter wire & the rest of that circuit must be upgraded.

 

[DirtDonk]

I'm with Steve on this one.
Every EB from 66 to 77 uses basically the same layout. The alternator's Black w/yellow output wire goes through the firewall and into the cab, is tapped for the fuse block, ignition switch and headlight switch, and continues on through the ammeter's induction loop. Near that point, there is a simple bullet connector and the wire color changes from Black w/yellow to either just Black, or Black w/red (depending on the year), and then back on out through the firewall to the battery.

So like said, EVERY AMP that flows from the alternator to the battery goes through that wire. And with the accessories tapped into the wire before the ammeter, when you show a positive charge, every bit of that indicated charge is read AFTER all the accessories get their feed. Which means that if your gauge reads 40 amps, you have 40 amps flowing from the point of the splice to the battery, but there might be more current on the alternator side of the splice.
It would be the reading on the gauge, PLUS whatever the accessories are using at the time.

The 78/79 ammeters are also shunted, just like the later model ones.
And they're notorious for never working.

An acquaintance used a 130 amp 3G with his Centech harness set up just like stock, with the Yellow wire attached to the alternator, the Red wire hooked to the battery, and no large cable hooked from the alternator to the battery. And while he did use it for a year with no obvious ill effects, he did change out to a larger directly connected charge wire anyway.
Just in case.

A friend with a '69 was not so lucky however. His setup with a 100+ amp GM alternator and dual batteries had a nuclear meltdown right in his driveway.
Something caused a high charge condition, and at least 2 fusible links didn't do their job, or had been removed at some point. I never did find any fusible links, but it was hard to tell what some parts of the harness were supposed to look like. Every inch of the harness looked like one big fusible link after a blowout! Melted plastic and some powdery blue copper strands everywhere.
Burned his whole harness right down to the bone in just a few seconds. I guess "luckily" though, that shut the engine down and ceased further carnage.
Fortunately, the guy with the Centech didn't have the same experience.

Paul

 

[Steve83]

Something caused a high charge condition, and at least 2 fusible links didn't do their job, or had been removed at some point.

If one wire gets hot & melts into another, the fusible links might not be in the circuit any more. Current flows to the LEAST resistance, which would be thru the ground short, and not NECESSARILY thru the fuses or fusible links. So it might have had fusible links downstream of the first melted spot. That's why it's so critical to put the circuit protection at the correct location: as close to the voltage source (battery or alternator) as possible.

Did he start & rev the engine before fully charging the 2 batteries? If the batteries were low, that could have been enough to melt the stock ammeter wire.

 

[DirtDonk]

Good point on the multiple current path once the shorting starts.
And yeah, thought of the low battery possibility, but they "shouldn't" have been too drained overnight. Theoretically that is. He couldn't remember if anything had been left on (unlikely) or if it had been particularly cold (also not likely), or if it had given him any hints in the previous days or so.
It was being used as a daily driver, but it was a semi-cold morning initial start, so the engine revs were a bit high. Nothing out of the ordinary though, and it ran for a minute or two until he got to the bottom of the driveway. Then, POOFFFFFF and HISSSSSSSSSSSS and spinning starters and smoke out the ying-yang. He had the presence of mind to open the hood and (with no wrench) yank the battery cable off the main.
All components were relatively new stuff as well. New is no guarantee of course, but it had been running for several hundred to a thousand miles or so before this.
About that many miles on everything from the starter to the alternator to the batteries and isolator, engine, trans, carb, etc. etc. etc.

The first thing I thought of was that one of the installers was kind of hacking things together. Overall though, wiring and mechanical was very elegantly done, but I did find a couple of things that I thought could be considered "hacks". I wasn't happy with what I could see of the charge wire's routing and connection to the alternator, but so little was left I couldn't prove anything to my satisfaction.

The other possibility in my mind was the firewall connectors on that '69. It's a bad spot and things get pinched and frayed under there sometimes without anyone seeing until it's too late. Here again though, all that was left of the charge wires were ugly melted holes through the connectors. You could shine a light from under the dash and see it under the hood. No wire left to inspect.

So it's still a bit of a mystery still. Works like a champ now though.

Paul

 

[Steve83]

I'd consider a battery cable that can be "yanked" loose to be a major problem. I like to think I can unload the suspension with the battery cables. But that's just me...

BTW
I finished that diagram & replaced it - I can't believe I left out the ALT light!

 

[DirtDonk]

Yeah, but I'm thinking that adrenalin had something to do with his success at the time. Might not have had them as tight as they should have been, but then again, he probably could have lifted the truck up on his own at that point!
I bet the battery cable never stood a chance.

I can't believe you did that either! Isn't that one of your pet-peeves anyway?
Is that the STA circuit you've got lighting the lamp? Keyed-on to the other lead of the bulb?
And speaking of which, will just about any bulb do the trick, even low-amp LED's?
Or is there a minimum load to do the job you're asking of it?

Paul

 

[Steve83]

I can't remember the name of the circuit, but it's the LG/R wire. I'm not sure if an LED will work, but I doubt it. The circuit needs SOME flow to energize the VR, even when the bulb is off, so an LED would probably either stay on all the time, or prevent the circuit from working. It should be a 194, and there should be a resistor across the bulb so the circuit is continuous even if the bulb burns.

 

[Hank Dodge]

My Bronco is happy now with a new 65amp alternator, a fresh regulator, and a new heavy duty AGM battery from Kragen. It looks like it's charging nicely at idle now even with all my lights, blower motor, etc. turned on as a test. My old system would go to discharge at idle when everything turned on, so this is a marked improvement.

Thanks again for all the advice.

 

[Hank Dodge]

Almost a week of driving it now and I'm happy as heck! So, this is how a charging system is "supposed" to work. I'm glad I went the route I did with it. I like keeping things pretty much stock as long as that's still an option.

Thanks again!