Bulkhead Connector Bypass Step by Step

[Dave999]

i've always been missing something 2 cylinders and an appreciation of the step-through italian style motor cycle...


...my wife says its common sense thats lacking, but i always reply with "how.... would you know?" which in general, shows a severe lack of common sense...

dave

[MattH]

265 Hemi six, more grunt than the 340 in Australia.

[petebryan]

Thanks again for all advice and contributions so far, all much appreciated. I've spent some time thinking through your comments and looking at options and further reading. I wanted to play back what my plans are to make sure I've not got the wrong end of the stick, with some further questions in terms of details:
Wiring:
* Plan is to add the new "big wire" from the alternator to the [starter relay] as Steve/Dave's recommendation.
* Am looking at a 95amp replacement alternator (see below), which means that (according to tables I've seen) that I should use a 6 gauge wire for that level of max power.
* Morgan's diagrams adds a fuseable link to that cable, whereas Dave's didn't mention that. If I add a fusible link it would be 10 gauge (again according to tables I've seen, being 2 gauges down on the main wire), but wouldn't that just reduce the current carrying capability of the cable to 10 gauge, defeating the object? Or is the logic that the fusible link should be the 6 gauge I'm after, so the main cable needs to be 2 gauge? What are the pros and cons of not adding fuseable link here? Is it relatively low risk to just add the biggest gauge cable I can find, to minimise resistance? Auto Electric Supplies do a 12mm diameter (40mm sq, about 1 gauge) that somebody else on the forum said they'd bought.

* Ammeter bypass: I will then remove the wiring from the ammeter and join the 2 sides up. Some people talk about simply putting both wires onto one terminal of the ammeter, whereas others talk about physically joining the wires up. I'd prefer the former as simpler - does anyone see any major disadvantage of that simpler route?

* Bulkhead connector: I intend to leave the cables in the bulkhead as they are (having reduced the load through them by adding the big wire from alternator to starter relay), as per Steve's plan.

Alternator:
* Powermaster do decent near-copies of my alternator but at 95amps. See https://www.summitracing.com/int/parts/ ... cation=int. That sounds like the right sort of number given that 95A is at the top end of its output, and so the low RPM level will be a bit lower, but enough to sustain my additional 20 amp fan and help with lights etc. I've looked at other makes (Denso, Tuff Stuff) etc and this seems as good as any, but any comments welcome. This Powermaster alternator uses an the external electronic regulator (so it is a straight swap with my existing original alternator I believer).
* My understanding from your very helpful input - and I want to check this - is that with the new big cable from Alternator to Starter relay wiring, little of the current should go around the rest of the circuit, so that I'm fine with the existing wiring. Does that sounds reasonable?

Fan wiring:
Looking at the wiring diagram for the fan - well actually the Davies Craig kit which contains a gauge, temperate controlled switch and wiring/relays - they say to attach the relay leading to the fan to the battery positive. I see that a number of US forums suggest that connection should be made to the alternator ('bat') itself. I've emailed the company to ask the question directly, who say that it's basically a workaround for the poor wiring and is therefore not best practice (though not being auto electricians they don't comment on whether it gives other problems). Given that there's going to be a new big wire between the alternator and the starter relay which then goes onto the battery positive, then am I ok running the fan (via relay) off the battery positive as recommended by the maker of the wiring?

thanks again

[cadboy]

I don't think it matters what size the alternator is, you need to protect the cables from melting if over current happens for what ever reason.

So protect the cable by a quick blow fuse, this way of current get more than the fuse then fuse blows.

I did the same on my car wire from alternator to starter relay. Put a 40 Amp fuse on the cable, first time I switch the light on it blow the changed to 50 Amps and it has been fine since. The cable I used is capable of 60 or more Amps.

Hope this helps.

[Blue]

First of all I'm not an electritian, I'm just going to tell you how I wired my cars. I use thinwall cable from Vehicle wiring products as its a lot neater for the power rating. On my 50amp alternator I use 75 amp cable with a megafuse to the battery positive. Ammeter is still connected but not much goes through that anymore. I solder and heatshrink all my connections for best perfomance. If you use magafuses then carry some spares, the recovery services are unlikely to have them.

[morgan]

Ref Fusible links - I used them as they were what was specified in the much-tried-and-tested MADelectrical diagram. They used AWG fusible links that were the size they needed to be for the loom - I am unaware that they do anything differennt to an actual fuse - they are just th'weakest by design' part of the loom and prevent damage - just like a fuse. I think its more that they are compact and bendy - you could just as easily use an appropriate BIG fuse. (in some ways this might be better; its easily replaceable)

Text of t'interweb says -
It is difficult to replace fusible links with fuses. Fusible links are compact and handle a lot of current before they blow. To replace the fusible links with fuses you will have to use mega fuses, the smallest will most likely be about 50 amps. And this will take up a lot of room, and be more connections to go bad
Doesnt sound hard to me - so if its easier than getting the fusible links then go for it.

Oh, I also disconnected ammeter completely rather than leave one pin but I cant see it makes any odds really. So long as you remove the running load of the car from the ammeter circuit (which you will have) then theory says its OK.

[MattH]

I fitted the Powermaster one wire alternator, a big wire (dont know the gauge, just looked big enough ) and connected the wires to one side of the ammeter.

[SJH]

First of all I'm not an electritian, I'm just going to tell you how I wired my cars. I use thinwall cable from Vehicle wiring products as its a lot neater for the power rating. On my 50amp alternator I use 75 amp cable with a megafuse to the battery positive. Ammeter is still connected but not much goes through that anymore. I solder and heatshrink all my connections for best perfomance. If you use magafuses then carry some spares, the recovery services are unlikely to have them.

Hi Blue what size (amp) megafuse do you use with your 50 amp alternator and 75 amp cable ?

cheers
Shayne

[Dave999]

and before you spend a lot on 95 amps

do you need it?

alternator provides what is needed to run car + whatever it can stick into the battery at the time, very much a just-in-time, supply and demand orientated device when coupled with a good regulator. which is part of a feedback loop.
Battery voltage goes down alternator is stimulated to do more work and vice versa

i.e battery voltage low, causes regulator to put the max 5 -6 volts into the alternator windings which produces maximum output for the few minutes it takes to slug a flow of max amps into the battery. very quickly the battery voltage gets north of 12 volts and the regulator tones down the voltage at the alternator coils to 0.5 volts or 1 volt or some such. this keep the alternator idling along producing just enough amps to chug a trickle charge into the battery and supply your stereo, fan ,lights, heater motor, wipers, ignition...delete as appropriate, an idling alternator is easy to turn so it robs little power from the motor. full charged battery gives maximum efficiency as alternator can be turned with your hand nice n easy.

so if that lot adds up to about 40 amps... and you have paid for 95 amps apart form 2-3 minutes when the battery is flat ish you are wasting 55 amps of the rated current supply in an over rated alternator.

this is the melt your ammeter reason for the whole bypass routine. whack in a big alternator, all is good until the battery goes flat then you kill your ammeter and melt the dash.

and boy o boy will it be stiff to turn when its full-on.. it will rob a load of power from the motor during that time

sling in two electric fans and an electric water pump and an electric vacuum pump electric fuel pump , jet engine loud stereo, and potentially an MSD that can suck up another 8-10 amps

or swap headlamps for boeing landing lights and you need some power

now we are talking about Modern car alternator outputs in the 80 - 180 amp (from a car with FI/ecu) style alternator.

size is dictated by type of battery environment application and amount of equipment i.e small plant doesn't have a big amp alternator, but a truck might so the illuminated playboy sign in the back of the cab doesn't Bananarama!....

yeah fuses or fusible link is good idea just cover exposed metal connections with vaseline and shrink wrap to stop moisture spoiling the fun 4 years down the line

Dave

[petebryan]

Thanks again for further replies Cadboy, Blue, Morgan, Matt H, SJH and Dave; all very helpful.

Fuses: thanks for your thoughts on this; I've read a bit more too and agree I should have some sort of fuse on the big wire (from alternator to starter relay). There are certainly pros and cons of both fusible link and big fuses. Interesting to see your quote in favour of fusible link Morgan, and to add to the confusion I've also seen discussions in the US forums where fusible link doesn't get the best write ups. On balance I'm going to go for a fuse. Whilst I know that's moving away from stock, it's a small component and should from what I read be more reliable and simpler to fit and replace (and good point re carrying spares Blue). I'm thinking I may go for one of the maxi or mega fuses (blade or more likely link types) from AES. I'm going to have a chat to AES about their fuses (or Vehicle Wiring Products, looks good as well - thanks). The AES mega fuses have continuous ratings and blow at 2*rating, so need their advice on how to match to the cable.

Ammeter wiring: sounds like both approaches to joining the wires work (thanks Morgan, Matt). I think my preference is to join the wires (rather than bolting to one side of the ammeter) as long as access is ok when I get in there, but as a fallback will attach both to single ammeter terminal if awkward to cut and splice wires in situ. Given that it's in the cabin, would I be ok to just find a nut and bolt to attach the wire ring terminals together, and tape up? Or is it worth cutting and join the wires (and solder and heatshrink) for a proper job?

Alternator: Dave, many thanks for that detailed analysis. I do take the point that I don't need 95A. There are a few bits to my thinking on this.
(1) What I need is something that will power the 20A fan in top of normal loads. I'm not absolutely sure of the output of my existing alternator but it's a non AC car and from what I understand that might be as low as 35A, so probably need 55A to include the fan. The other complicating factor is the low RPM performance of any alternator, given fan is required when engine is at idle. The Powermaster one I found gives 50A at idle so seems a good match.
(2) I want to keep as close to stock looking as reasonably possible on the bigger components in particular and the Powermaster retro alternators seems to be a very close match, both in terms of looks and fit, so I think I can just replace my original with a new one and it will fit perfectly in terms of brackets and electrical connections (though planning to check if my existing regulator will be ok).
(3) I've not found a lot of comparable alternatives out there. Denso was mentioned but I can't see any that they currently make that are retro style like Powermaster do.
(4) 95A is the lowest output that Powermaster do. Whilst I completely accept that it's overrated for my current needs, by adding the "big wire" and bypassing the ammeter I've reduced the potential risks substantially, and if the car only ever draws 55A ish then I'm only living with a bit of extra cost for the overrated alternator (and hopefully that engine power loss you mention won't be too significant!).

All that said, am still up for other suggestions!

Cheers again!
Pete