Diode In Alt Sense Line To Raise Voltage Output .

[discopotato03]

I notice that people at times have charging issues and alternators that put out less than optimal voltage levels .

I'm told that with higher voltage you have less current doing the electrical work so lower voltage levels are not good .

I did some research and it seems that the greenies have bitten into automotive engineering with charge systems - basically slightly lower charge voltages need less engine power to drive alternators so I'm thinking late engines may show better consumption - and emissions numbers particularly at cold start .

My understanding is that with a healthy alternator its regulator sets the output voltage and as long as it's spinning fast enough and the amperage draw isn't exceeding its capacity it should maintain the correct system voltage .

Alternators from our Skyline era (say 1989-2000) generally have three wires attached . The big ones are the current output and the two smaller ones are for the dash warning light and a battery voltage sense line .

My experience is that alternators charge at a slightly higher voltage in a cold engine bay and drop off as the engine bay heats up . My S2 GTS25T starts out at around 14.2V with the coolant at 20C but once warm ends up at around 13.8-13.9V standing in daylight with the hand brake on ie no lights including brake ones . No AC sound cig lighter or obviously demister going . This is with the OE Mitsubishi 80a alternator too . As a side note Just Jap tell me only GTRs got the 90a version for the five extra computers etc they have to run .

Anyhow from my readings it seems that it wouldn't matter if you had a 200a output alternator if the voltage regulator regulates at 13.8 volts hot then that's the highest voltage level you're ever gonna get regardless .

Enter the simple dirty cheap but apparently reliable fix .

That battery sensor wire tells the alternators charge reg what the battery voltage is and if it's low then the regulator get more generous and makes the alternator put out higher voltage . A simple method to trick it is to put a diode in the sense line that makes the regulator think the battery voltage is around half a volt lower than actually is so it charges half a volt higher than it normally would . So in theory I'd get 14.7 volts at cold start dropping to 14.3 at running temperature .

The thing to know is that an alternator will charge a battery faster at a higher voltage than it will at a lower voltage and a cold start takes a significant amount of current out of a fully charged healthy battery .

A battery is called that because it is a battery of six 2.1 volt cells and the best it can put out without help is 12.1-12.2 volts if there is zero loss in the wiring which is never . So give it a dead short across the starter motor to turn over lazy flock of a cold RB and it takes a fair bit of current out .

The 4WD camper people are all over this with their multiple battery systems to charge , they often use two and isolate the cars one so they can drain the auxiliaries overnight to keep the cans cold and still start in the morning . Deep cycle batteries can be drained reliably and still charge up .

With us if higher voltage means less current is needed to drive our go fast bits this should be good . You'd think 14.4 volts to things like coils injectors and fuel pumps has to help because low voltage to these things never does . It's the higher current draw from lower voltages that increases resistance and heat at inadequate parts of the system . Higher voltage requires less current draw to do the same work but don't get too greedy with voltage .

The things to look into would be firstly a healthy alternator because giving a ailing one purple hearts will probably only take it out faster or damage other things . Secondly higher voltages into batteries in some circumstances can make them boil the water component of their acid away faster . Some us are lucky that the battery isn't in the engine bay so it isn't copping heat from the engine or radiator . Still have to check the levels periodically .

Always check voltage output at the alternator if you have voltage drop anywhere in the electrical system , the output could be fine there but lost to old or inadequate wiring , bodgy mods etc . Could be high resistance wire joins to terminals or bad earths . Factory looms have crimp joins inside them and they can be iffy if aged or corroded . 1989-2000 was 14 to 25 years ago so my 96 wiring system is 18 years old , old enough to vote ...

Anyway if the system is good - or made good - but the alternator only wants to loaf along at 13.8 volts fooling the sense wire may be a way to get better performance from factory fitted - but in good condition (freshened up) alternator .

I have read about some late cars charging as high as 15 volts but I think the Power Train Control module or PCM has a say in when they do it . I don't know if they need fancy batteries or temp sensors to do it reliably but with the electrical bullshit in "modern" cars now days nothing would surprise .

Thoughts ?

Cheers A .

[89CAL]

2.1 volts x 6 cells is 12.6v

remember that voltage is like pressure and current is like flow. You can't change one without changing the other. Electrical components will draw the current they want and need and this will have an affect on voltage.

I'm not real sure that tricking the alternator is going to net you proper gains, because everything is relative. If its trying to charge the battery to a higher voltage then it will either be putting out more current then it normally would or putting out higher current for longer then normal.

Perhaps I'm missing the point but for me, if your charge system is healthy (above 14v) then why mess with it?

There's little to be gained from playing with the alternator in my opinion. You just want to see stable voltage and the right voltage

[discopotato03]

Where practical higher voltages have the advantage of lower current flow which is why many trucks have 24 volt systems , to keep the current levels sane .

It must be 20 odd years ago BMW were contemplating 36 volt car electrical systems , one thing mentioned was really fast electrical heating abilities of higher voltages for the cats and 02 probes they were looking into . Was never going to work at 12 v .

Higher voltages would allow manufacturers to use thinner lighter cheaper wiring because with higher voltages you have lower current flow so don't have to allow for the thermal loadings of higher current flow .

Ever wondered why some wires in your loom are impossibly thin , it's because they have very low current requirements . Some are quite heavy because they are designed to cope with high current flows which would overheat thinner wires with the same current flow at the standard voltage .

Anyway I am talking about a whole half a volt not 5 or 10 and if you can take some of the current load off the electrical system and its components without damage I don't see it being any disadvantage .

Actually I was here 20 plus years ago in the days of the Bluebird , it had a Bosch alternator beefed up to I can't remember how many amps capacity with Bosch Holden guts . It also had a optional voltage reg made to run 14 .7 volts instead of the standard 14.2 . The only drama it had was a 7 volt tap for the original carby choke heater and at start you had to give it a rev to make it start charging . Everything ran bright and it never burnt or boiled anything .

A .

[discopotato03]

This is an interesting read from a Fourby site called IH8MUD.COM . I can't post links ATM so search

Alternator Regulator Voltage Booster Modification - Part 1-Introduction .

Interesting because some of these four wheel drives are from our Skyline era and Japanese manufactured .

If you can post the link I'd appreciate it .

Cheers A .

[Ben C34]

Whilst I agree the higher voltage is better due to the reasons you listed, you would at best be looking at a 5% gain. Really doesn't seem worth it to me.

[Ben C34]

http://forum.ih8mud.com/threads/the-alternator-regulator-voltage-booster-modification-%E2%80%93-part-1-%E2%80%93-introduction.602982/

Here's your link

[89CAL]

My point wasn't that it wouldn't work. It was as above, so much effort for what gain? I've never had an issue with my electrical system. ECU'S compensate for minor voltage variances, but as per my original point, if your electrical system is working properly and in good condition I don't see any need to Change it

I'm not at all trying to shoot down new/different ideas, but I just don't think it's worth it. At least I can't see the point on my car

[jiffo]

You meet all sorts when cruising and one old bloke had, in an previous life, built up and sold his radio manufacturing company, so he was pretty clued up with electrics.

The charging system on Stan's yacht, (Westward, 48 and 49 Hobart winner) had been modified by him with a rheostat to trick the alternator into thinking the batteries were flat.

He'd have the fan belt screaming on that engine, batteries were charged up in no time.

But he monitored it carefully and knew what he was doing.

Would be easy to boil the batteries or buckle the plates.

If your alternator is in good condition with good brushes etc, and the voltage reg is actually working properly, modern systems work very well.

Biggest problem with old Skyline alternators is their voltage reg.

2nd most common problem is rooted alarm siren batteries which continually drain the car's battery.

[discopotato03]

Actually peoples I took another look at this and yes it's not the best way to go about lifting alternator output voltage .

I'm not an electrician and had a steep learning curve recently with RB alternators and R33 wiring systems .

Basically early R series used Hitachi LR180 or LR190 alternators the 90 apparently being in GTRs , Just Jap reckons 5 more computers to run in them .

Later R series went to Mitsubishi alternators in I think the 100mm rotor series . I haven't got to the bottom of the internal difference between the 80 and 90 amp ones but I think it could be a couple of extra windings in the stator with possibly the same rotor . BTW if anyone gets the 80a Mitsy rebuilt and can't find local support the regulator is same as EB Falcon .

Now to R33s and wiring . I'm beginning to wish the coupes had the battery up front like the sedans do to get it closer to the alternator because it's a lengthy cable that goes under the drivers side and crosses over further back to get to the + battery pole .

Today I'll be testing what the voltages are like from the alternator back to the bolt on the relay/fusible link box and to see if there is any difference between the two bolts ie the one from the battery cable .

Something I didn't previously realise is that the alternator sense wire in many cars splices back into the main feed out of the alternator so it's sensing what the alternator is putting out voltage wise , not what voltage the battery is actually getting .

On one site I was at the sensing can be described machine sensed or battery sensed , machine being the alternator . Some of the 4WD crowd are getting good gains by running an extra parallel feed from the alternator to the battery and moving the sensing point from close to the alternator to the battery itself . You can imagine a situation where because of voltage loss in old looms the battery may only see 13 or less volts and never charge right up .

The right way to make sure the alternator senses what the battery is getting is to use it as an alternator sensing point but you also need to make sure that you don't have significant loss between the alternator and the battery .

When last tested my car showed I think 1/2V loss from the alternator to the battery and my EMS shows 14.2V at cold start and around 13.8 hot in the daytime .

Ideally I'd like to have 14.2 hot running at the alternator and as close as possible to 14 at the battery so we'll see what can be done . I may not get that sense point all the way to the back but maybe the battery side of the under bonnet relay box may help if there's any loss between there and the alternator .

I also need to trace where in that relay box the wires on the external plug connectors go (behind washer bottle) , especially the upper one that's full of white gunk .

More later cheers A .

Uh BTW I have not seen what the Nissan spec is for voltage output at the alternator itself , Australian/European Z32 300ZX NA and TT is 14.1 to 14.7 volts and aside from layout specifics an R33 probably isn't significantly different .

Can someone with a full R33 WSM in English look this up please .

Cheers A .

[89CAL]

I'm still unsure what you are trying to achieve with this, or is it just a case of 'doing it to see what happens/how it works?' in which case that is fine and I understand that completely

If you are chasing a battery voltage problem, then remember that the battery is only feeding a few things in the rear of the car and the main supply to the relays etc in the front section of the car come from where the Altenator and battery cables join on the terminals in the relay box in the engine bay (On R33s)

So basically if your altenator is happy that its putting out the right voltage up front, then the main electronics in the car will be getting the full altenator output. I don't have any voltage problems with the Link, the only time I have minor problems is first start up after I've been out at work for a week and the car has been sitting there the battery voltage is sometimes a bit lower then I would like for starting the car, but still does the job fine. Running the sense wire to the battery terminal at the rear is probably not too bad an idea, but this all depends on what your actual voltage drop is between the altenator B+ terminal and the battery positive terminal. If its <0.3V say, then I would probably be happy to live with it. If you are getting half a volt difference as you said you did last time, then maybe it would be worthwhile doing that. But this will put more strain on the Altenator (not excessive, just more)

As for current output from the altenator, I'm struggling to remember what determines this. It will of course depend on required output (i.e if the battery is already near fully charged, its not going to output maximum current), rotor speed and size/quantity of windings. I cant exactly remember how it all comes together, but I think the voltage reg plays a small part in it as well, in that it limits the voltage output so must have an affect on the current output also. I vaguely remember any of the stuff I did on altenators at Tafe, and we did quite a bit on them (even playing with one on a test bench where you can really see how much load an altenator can put on a motor). Due to the industry I work in, there isn't alot we do with altenators. It either works or it doesnt, and then we change it out. So I dont ever think too much further into it then that. I have my ways to test it and thats about it

[discopotato03]

In my particular case I fixed 90% of my probs with cleaned up the engine and bay earths and running a new regulator and brushes - in the OE 80a Mitsubish alt .

I suppose those that remember will wonder why I didn't go with the Maxima Hitachi ones but that's another story .

Back at the alternator terminals my S2 R33 has the thin wires in pale green for the sense and white with a red trace for the light circuit .

They come back out of the loom before the front eye fitting on the relay/FL box and go to those two plugs behind the washer bottle , green to the upper plug and the W/R to the lower grey connector pair . We did a voltage check on the green one and it was very close to the alts outlet at ~ 14.2V . In fact all voltage checks are now good including the battery poles which are about 0.2V below the alternators readings .

Back to alternators . If you search Nissan forums in the US they use Nissan Quest alternators because they are around 125 amp and fit with a few simple mods . We didn't get Quests here , they are a VG30 or VG33 powered people mover bread loaf type thing . I didn't realise we had VG33s here but it turns out that 96-05 Pathfinders used them and they had 110a alternators with mounting ears more like RB alternators have . Most of the larger Nissan alternators have the wrong front case ie Maxima transverse VG and VQ V6 ones . And they are bulky meaning if you fight your std 80a Mitsy alt out and in good luck slipping the large case ones down through the looms and top rad hose , probably easier from underneath if you don't run the splash guard .

Many auto sparkys don't like Hitachi alts and seem to prefer the Mitsy ones , some Quests and Pathfinders have Mitsy alts and I reckon if you get the right casings you can make high enough outputs to run most things . Cheaper than those blue painted bling alts too . From a bit of searching Pathfinder alts aren't real exy 2nd hand .

Something I'm looking into is the OE GTR 90a alts because unconfirmed but they may be a family up from the 80a RB20/25 ones using 106mm dia rotors rather than 100mm ones . If the higher capacity longer stators and rotors go in them it may be possible to have a bolt on hybrid that would cover any performance mods like those 20a draw fuel pumps . Or with a bit of grinding and drilling the Pathfinder cases can work .

A .