Technical Painless Wiring Warning

It's actually hard to tell where that wire from the alternator went to in the fuse panel, almost looks like it goes to the unused acc terminal.

 

For comparison sakes this is the current Painless 10102 fuse box

 

If I may I have been following along and to ignore the alternator/starter fuse debate monentarily am I correct in my understanding that one of the biggest issues with these pre-made looms is that its only one 10 gauge wire feed for fuse block?

If so rather than 1 or 2 x 10 gauge, would 2 x 8 gauge wires (constant and switched feeds) resolve that issue for a car that is only running basic circuits plus the addtion of some USB chargers for phones and a bluetooth speaker? If so do any of the harness makers do that? Failing that any issues with upgrading a commercially available harness to 2 x 8 gauge inputs. Or for my car am I just over thinking it?

Apologies if the answers are obvious for some and the multiple questions, just trying to get my head around all this before getting into it and do appreciate the schooling

 

Over thinking it.

Basic car doesn't need 20+ circuit panels or one of those 100 amp one wire alternators for that matter.

 

Actually, those are very good questions and the crux of the matter here.

As far as I can tell, pretty much every aftermarket harness supplier is selling near-identical product. They almost all feature switched and unswitched branch circuit outputs like the OEM panels. Where the problem comes in is how they supply power to the panel. Painless appears to use two #10s to the unswitched side then has an internal connection to feed the switched side through an output to an external switch (in our case, the ignition) which then returns to the panel to feed the switched branch circuits. This is limited to a single wire and 30 amp fuse, so that's the limit for your switched loads. Remember that nearly all ignition switches are only rated for 30 amps at the very most anyway, some are less. I suspect these panels are mostly all the same regardless of manufacturer. One thing you won't find is any notice of the maximum current rating of the panel itself or a panel schematic to understand what they did. The one exception I found is American Autowire does offer a 'severe duty' harness kit that is capable of up to a 200 amp input, but it's over $800! Not to mention overkill for our uses.

You should NEVER directly connect the alternator output to the fuse panel.

So, what to do? If you really do have a bare-bones car, these panel kits will usually work, but I always caution to do a load calculation making sure that the connected continuous loads don't exceed 60 amps total or 30 amps to the switched half. Yes, there are ways of 'cheating' this to get somewhat more capacity, but it introduces other issues and compromises like $50+ 'relay kits' to fix this which could be easily avoided if they'd fix the panel/feed capacity issue. And while I'm on this subject, do your load calcs before you buy a kit. I'm sure most buyers count up how many circuits they need and order a kit with that many fused connections. But what happens when you run out of panel/feeder capacity before you run out of circuits? Or run out on one side or the other in the panel? Entirely possible to do, and the kit seller will 'correct' this with a relay kit. One more problem... you thought by getting a fuse panel with enough circuits you'd have all your fuses in one place. That is no longer true, each one of these relay kits will need its own separate power supply with its own fuse. Located at the same point where the panel feeder comes from. Again, all this is just one of the reasons I won't use one of these kits.

Here's what I use; the Bussman/Eaton series 15600 fuse panels. 2013 Cooper Bussmann Transportation Full Line Catalog (mouser.com) . Available in 4 to 20 fused circuits and the panels are rated for at least 100 amps connected load, with each individual circuit accepting a 30 amp fuse. They're even available as a split panel, with each half good for 100 amps. They also use 1/4" blade connectors for the branch circuits, a lot easier to work with under the dash if needed. Who wants to deal with little bitty screws in cramped spaces? Not me...

These can be found lots of places; Amazon, eBay, electronics suppliers like Mouser to name just a few. The 'common' sizes are 4, 6, 10, and 12 circuit unsplit panels, between about $25 and $35 each. Some of the configurations are probably special order ($$$) and I'll note that the panel specs given in some places are bogus, the numbers above are straight from the manufacture's data sheet as seen in the link above. I've seen some 'off brand' copies for half the money, they may be fine as this is a pretty simple design. I should order one for a comparison...

If you go this route and your connected load on the switched panel is close to or over 30 amps, you'll need a large relay to supply power to it to protect the ignition switch. McMaster-Carr offers both 80 and 100 amp relays that will do this for about $30. electrical controls | McMaster-Carr Look for part numbers that start with 7995K. The last two numbers (not shown here) will ID the individual relays. Note that these have BOLTED connections; DO NOT use plug-in relays at these amperages. This also allows you to run ONE larger wire to the fuse panel relay to supply both sides, with just short jumpers to the two panels.

So at this point, do you go all in and build the whole harness? You'll have to figure out circuit loads and wire sizes (which you really should be doing, whether you use a kit or not), then purchase it all. Certainly not impossible to do, more time consuming than hard, but it can be a PITA. Or you could buy the kit, cut the wires off the panel and re-connect them to the new panel. It is nice to have all the colors needed and every wire identified. Two caveats here; one, the kits tend to skimp on wire size IMO (the other big reason I won't buy them) and two, just because the kit has the right number of circuits/wires you need doesn't mean the wire sizes will be correct for what you have. So you'll likely end up buying at least some wire.

 

Thanks so much Steve, once again great info! Really appreciate the detailed response.

`You should NEVER directly connect the alternator output to the fuse panel.`
So both feeds, if they are seperate (constant and switched) from the starter solenoid?

 

What besides heat are the indicators of an undersized wire? Loss of volts? Loss of amps? Say for example the alternator to battery wire.

 

If the alt is regulated there may never be an over amp/volt event. It should self adjust its output safely whether internal or external regulating is happening. A 95A alternator will supply that on demand, not 100% of the time and somewhere between max RPM output and shunt. Thought I'd toss that pinch of salt into these recipes...

Or, if someone knows better and I'm full of shit tell me. I can take it.

 

The very first indicator will be voltage drop. This will appear before the heat does. If the wire temp (and resistance) goes up enough, current will also drop. UNLESS it's supplying a motor load. Motors are different, any voltage loss will cause current to increase as the motor continues to try to deliver the same amount of power. This will accelerate the temp rise in the wire.

 

That is exactly what Ford did on my 2005 Aussie Falcon.

There is a H/D Red wire from the battery to the starter motor [a normal standard practice]
And another H/D Red wire from the battery to the Fuse Box
There is also a H/D White wire from the Alternator direct to the Fuse Box.

Both the Red and White wire in the Fuse Box are connected together by a Bus Bar.

 

That's not the same thing as we're discussing here...

 

Thanks. So if sized correctly, with engine and accessories on, voltage (or current if possible) measurements at alternator and battery should be the same, or close to it?

 

I've read through most of this thread, skimmed through the rest. I used a similar Painless harness in my 56, not sure of the model but I remember scratching my head when seeing the B+ diagram. I am running a 120a alternator as it came with the engine accessory drive kit I purchased, here is my solution.

To simplify it, these circuits are what "powers" the Painless fuse box, that's it... It would NOT handle my 120a alternator's output if it went full tilt.
- I grouped all these feeds together and ran it to B+ on the starter with an appropriate sized circuit breaker for the fuse box.
- I ran a #4 wire from the alternator directly to the B+ on the starter.
- I did build a separate and protected relay panel for some high current accessories

On another note, my son was having some charging issues with his OT 1982 D150 truck. This is a bare bones truck, no PW, AC or any other modern conveniences. While diagnosing I checked how much amperage his truck drew with the headlamps, wipers, heater, and electronic ignition system going, it was 55 amps so plan accordingly.

 

It depends... LOL. If measuring between two points on a wire and nothing is connected to the wire in parallel in between those points, the current will be the same at each end. You will always have some voltage drop in any single piece of wire. By sizing it 'correctly', you are simply reducing the drop to an 'acceptable' amount. Now, what is acceptable can vary widely depending on who's doing the calculations and how much compromise in circuit operation they're willing to accept. Personally, I won't allow a drop any larger than 5% in any given circuit. Once you start getting much above that you will have some degradation in how things may work. At 10% or more, it can be obvious in some circuits, mostly lighting which will be noticeably dim but not good even in the others.

Where it gets sticky is voltage drops are cumulative, i.e. they add up. As an example, let's say battery voltage is 12.8V with the motor stopped. Start the motor and the alternator outputs 13.5V (call this point A). But the voltage drop in the wire connecting the alternator to the connection at the battery (call this point B) is 5%, so delivered voltage at the battery is only 12.8V for no gain. Next, say the fuse panel feed wire is also connected at point B and goes to the connection at the panel, point C. If you have another 5% drop between B and C, now your down to about 12.2 volts, or a 9.1% total drop, not even battery voltage. Any drops in the branch circuits will be further losses.

The OEMs know this and compensate for it by using a 'sense' circuit in the regulator using a 3-wire alternator. This is connected 'upstream' at the fuse panel or ignition switch and will boost alternator voltage output until it 'sees' 13.5V at that connection. Output now measured at the alternator will be 14.7V to allow 13.5 to get to the main part of the harness. This is why 1-wire alternators aren't a good idea in most cases as they don't have this feature. They can work, but wire size between them and the rest of the harness becomes critical.

I'll note that the numbers used above are for illustration purposes only, yours will vary. But they do show the relationships.

This is why I stress that doing load calculations along with voltage drop calcs is important for each piece of the harness. I try to achieve a total drop of no more than 5% at the end of each branch circuit. This means the individual drops have to be much less than 5%, I shoot for 1-2% in the alternator/panel feeds, that allows up to 3% in the branch circuits. Just try to keep your total drops down as much as you can. If you're using an aftermarket harness kit, it may be impossible to do because of their designs... Which is why I don't like the kits.

 

It also depends on where you place the ampmeter as to what it shows.






Bones

 

Most ammeters are placed between the Battery and the Generator/Ignition switch circuit.
That way it measures charge and discharge [except for the starter motor which would fry the ammeter]

On a 3 terminal ammeter [56 Chevy pickup] One terminal goes to the starter motor as the 12v battery feed.
The other 2 go to the generator/ regulator and the Ignition switch [these 2 are connected internally]

The problem that scares people with ammeters is all charge and discharge goes through them, and the ammeter acts like a resistor generating heat.
Most ammeters are limited to approx 30-35 amps and then they will Chernobyl themselves.
Many have tried patch up "shunts"/bypass wires to divert the flow but this alters the behavoir of the ammeter [reading only 1 direction , or altered scale etc etc]

The best method if using a 65a or larger alternator is to make a "Hybrid Shunt" wire that bypasses around the ammeter.
The Hybrid Shunt uses 2 "forward drop diodes" in opposing directions [parallel in this wire]
The diodes have a fixed value of voltage drop to open them, whereas the ammeter [acting like a resistor] has a progressive/non-linear voltage drop.
Below 30a there is less voltage drop across the ammeter than to open the diode, so the ammeter flows current.
about 30a and higher there is a point where internal resistance in the ammeter starts exceeding the forward drop value of the diode so the diode will flow the excess current.
This ^^^^ usually happens when the ammeter is "maxxed out" on its scale. [after cranking over an engine]
Once the battery recovers [enough] the ammeter reads as normal.

Use 2 x Vishay 150a rectifier diodes connected together parallel [back to back] mounted inside an old regulator box.
These have a 1.13v forward drop
The diodes behave like a "pressure bypass valve". Also if the ammeter totally fails this will not leave you stranded on the roadside.

 

Or you could use the high amp Stewart Warner shunt amp meter, like we do on fire trucks.






Bones

 

Inductive ammeters have been around forever. The meter carries no current. So, why haven't they been used more?
AFAIK, Ford was the only automaker to use them as standard equipment. And, if you look on the net for auto amp gauges, 99 of 100 will be the 'normal' kind. But there are a few inductives still available.

Seems to be a perfect solution, unless they are not as accurate. Even that would be better than fire! in an overload situation.

 

Those work somewhat similar to the Stewart Warner shunt high amp ampmeters. Some OEMs saw the wisdom of not running huge current through the dash.




Bones

 

I had an inductive ammeter in my ‘42 Ford PU, i then went on a hunt for an inductive DC ammeter “meter” like a DMM, etc. price was cost prohibitive, years back maybe the cost wasn’t as much different? For a dash gauge.
I don’t think accuracy for the most part would be a concern in a vehicle. At least not for me, I’m not concerned if it 10 or 13 amps charging, more concerned about charge or discharge for the most part.

 

Accuracy is one issue. As well as the hassle of getting that high-amp wire to the gauge location then back to where it belongs. But the real issue is an ammeter isn't the best choice for monitoring the operation of an alternator. Detroit stuck with them far longer than they should have once they made the change from generators. Why they did that I can only guess; inertia, re-educating the owners, who knows. You won't find one on any late model cars. If you're running an alternator, a voltmeter will give much better monitoring info.

 

Just for you Mike



There are a few posts about converting ammeters to voltmeters etc etc
Why is that???
Because a lot of people don't want to butcher the dash for an aftermarket gauge.

The whole purpose here on HAMB is to preserve traditional hotrods [as best as possible]
With a bit of intelligence and basic skills applied can provide a very practical solution.

That is the purpose of the Diode Shunt [Hybrid Shunt] , The stock ammeter works perfectly in normal daily usage. And the original harness is still up to the task.
The shunt's purpose is to bypass excess current draw if the situation ever occurs.
[eg: after cranking over a vapor locked engine over then it starts, the battery draws excessively on the alternator]
You can connect the Diode Shunt [Hybrid Shunt] from the Alternator direct to the battery and not even touch the harness.

 

But it still won't properly monitor the health of an alternator system... which is the point of having the gauge. If you want one for decorative reasons, leave it disconnected and use an idiot light mounted in an unobtrusive place.

 

Interesting... my Dad gave me a wiring kit he bought for his hot rod 15yr ago. Was too complicated.... so he sent it to me. Still in the
Box.. I need to see who made it now.

 

I've been trying to understand the relationship between charging voltage and battery voltage. As I understand it, charging system voltage can run into the mid 14s, and fully charged batteries in the mid to high 12s. Why the higher volts, if there is sufficient current to charge without it?

 

That is one bendable thumb you got there. I just tried that, ain't happening.

 

The higher voltage is needed to 'push' the current into the battery. If the charging system is only putting out the same or less voltage than the battery, no charging will take place. How much current is being made won't matter.

 

Thanks. Is there a limit to how much higher the voltage can be and if so what happens if it's too high?

 

Seems to me the upper limit is about 14.3V IIRC. Above that and battery damage starts to occur. On the old non-sealed batteries that meant you had to add water to the cells. But the amount can vary by manufacturer, you'd really have to check the OEM specs. Ford used to be the systems that ran the 'hottest' in that respect.

 

There'a lot of knowledge here! This thread couldn't have come @ a better time, as I'm about to re-wire the Plymouth with a Painless kit... been putting it off four 6 years. (We don't want to rush into this sh...tuff)