High amp alternator help

[MagnumForce]

I have a 340 small block with an electric power fan and an electric fuel pump. I plan on installing a basic stereo in the future. I want to install a higher amperage alternator, like a 140 or 160. My stock one is just simply not enough anymore. The one I'm currently looking at is the powermasters 2 v belt model. My engine has only one belt so would I be able to use said 2 belt alternator with my single belt. I haven't been able to find a one belt alternator that will run that high of an amperage so I see this as my only option.
Any help will be appreciated!

[WHITE AND RED 69]

140-160 amp alt is overkill and I don't know if I would trust the stock wiring to handle it. I'd go with a 100 amp alt with some wiring upgrades like a volt meter conversion. And your choices for a 100 amp alt are far greater. So finding the right one should be no problem at all.

I run a Tuff Stuff performance 100 amp alt with dual electric fans, modern stereo, and modern lighting with no problems at all. 

[MagnumForce]

Thanks for the advice i will look into the 100 amp 

[b5blue]

Check out the Denso 120 amp at Mancini Racing.

[Ghoste]

And I'll echo the wiring upgrades you'll need to do.

[Pete in NH]

Hi,

If you're going to put in a 100 to 120 amp alternator and actually use all the current, you will have to upgrade some of the original wiring. Keep in mind the original alternators were 35 to 45 amps and the wiring was barely adequate for that. At anything over 45 to 60 amps you really can't use the original dash ammeter and should convert to a voltmeter. Also the original fusible link distribution will no longer be adequate. Big alternators on these cars opens up a real can of worms unless the electrical system is reworked in specific ways to direct the current around to things safely. If you post a list of what you have already installed in the car or want to install we can work out the details.

[Dino]

Dammit I knew I forgot something, I have to get abigger alt as well.  The Mancini one has been out of stock for months now unfortunately. 

So there's no way to keep the ammeter huh?  That sucks.

[Ghoste]

Its just that it was never intended to handle that amount of current.  Combine it with 40 year old wiring, a bunch of high draw electrical requirements that never existed when these cars were made and the Achilles heel bulkhead connector and its a recipe for the electrical fire that everyone blames on bad engineering when we just keep asking the system to do things it was never designed for.

[Dino]

Its just that it was never intended to handle that amount of current.  Combine it with 40 year old wiring, a bunch of high draw electrical requirements that never existed when these cars were made and the Achilles heel bulkhead connector and its a recipe for the electrical fire that everyone blames on bad engineering when we just keep asking the system to do things it was never designed for.

Yeah making mods to the electrical makes me nervous, and my wiring is in great shape.  I would love to keep the ammeter though but of course I could just get a volt meter instead and slide the stock cover in front to make it look stock.  I'm still not sure what all has to be done to the wiring to support an alt like that but b5blue has a real good write up so I'll have to study that again.

[Pete in NH]

Ghoste, you said it perfectly. That's exactly the issue when putting big alternators on these cars.

[Nacho-RT74]

there is something wrong on what has been said.

you car requires 40 or 50, or 30 amps ( whatever accesories you are using ) no matter the alternator you are using. If you have enough alternator power, everything will be sourced from it. If not, the power will be provided by both at the same time, batt and alt, BUT ALLWAYS the same amps the car demands. That's the moment you need to save to keep ammeter safe, saving from load coming from battery.

THEN reinforce the weakness of bulkhead, AND THIS IS EVEN WITH STOCK 40-50 AMPS used from factory. OR ISN'T TRUE WE GOT BURNT THE WIRES/TERMINALS WITH STOCK ALTERNATORS ?

A tipical big mistake is get a HIGH RATE BATTERIES keeping stock alternator, because this is one more of the reasons to get ammeter and wiring burnt, because stock alternators never gets to get fully charged these batteries adding ore stress on ammeter and wiring. Better a bigger alt and stock battery than backwards.

you can get a thousand amps alternator, but if your car demands 40 amps, the thousand amperes won't be ever sourced, just the 40 amps required by the car.

an example of a tipical home daily deal:

you get an GIANT POWER ELECTRIC PLANT able to feed with thousands of volts and amperes which is sourcing your home. Then you get maybe a 20 amps breaker on circuit to source one ( or couple ) wall outlett where you charge your cellphone which only sucks 0.5 amps, and you don't burn your cellphone charger.

got it ?

[Pete in NH]

I agree with Nacho that even stock alternator cars should have the wiring between the alternator, ammeter and battery upgraded. The bulkhead connector pins are a real weak point in the design and the wiring is a bit on the light side. After 40 years of use,abuse and age, it's time to upgrade to heavier wire, bypass the bulkhead connector pins and replace the fusible link with something a little more reliable.  And it's very important that the ammeter terminals be clean and tight.

I see the issue with big alternators as if there is ever a demand for all those amps they will be available and flow somewhere. That I think is the trouble spot. Yes, if the present load requirements are only 30 or 40 amps that is all the alternator will source. However, if the battery is really down or a short circuit develops somewhere, That big alternator will pump out more current than the wiring or particularly the ammeter can deal with safely.

My 71 was ordered with the optional group 27 big battery and I've always had a group 27 in it. I've never really seen prolonged high rates of battery charge. Even with the A/C on, stopping  at a traffic light for a few minutes, while the battery does provide the needed energy it is quickly replaced and the ammeter falls back to center.

[hemihead]

I have been thinking about this and when I do my Bypass , would it be better to substitute a Volt gauge and eliminate the Amp ? And from the research I've read there seem to be 2 different Denso Alts . One with an external Reg and one with internal . Is that right ?

[Pete in NH]

Hi,

If you're going with a big Denso alternator my preference would be to use a voltmeter instead of the original ammeter. An Autogage 2356 1-1/2 inch voltmeter may fit right in place of the ammeter if you take it out of its case. The original ammeter is only rated to handle 45 amps or so. Some one more familiar with those Denso's can possibly answer your regulator question.

[elacruze]

First of all, you can't develop more than about 100 amps with a single V-belt, no matter how tight the belt.

I used an ~80amp alt from an '86 Dakota. I have EFI, power windows, A/C, 300w stereo, and cruise control. I've never had any issues keeping the battery up.

[b5blue]

  To clear up about the gauge: It does not read total AMP output, it reads the difference between battery voltage and regulated load output. THAT reading should be "needle centered" under normal operation. If the battery is low it will show + reading and if drawing off battery it will show -.
  Yes if for some reason you had "runaway charging" it could be dangerous....but regardless of the type of Alt. you would "shut down" in that case, right? What if you had "no charging at all" would you continue to drive the car? Bypassing the gauge in ether of these examples would mean "you have no idea it's happening".

  It's intended use is to warn of something failing before it's "catastrophic" by indicating the degree and direction of the fail.

  The reason I chose the Denso 120 Amp was entirely ability of low RPM Amp output. (50-60 Amps.) Because that is how much I need to sit at idle and run ignition system and add all my lights, the blower for A/C or defrost, my wipers on high and the rear window blower I'm adding. I found no other Alt. that fit and functioned as the factory engineered my 70 Charger. Yes I have and will install a new "OER" AMP gauge as it's rated @ 60 Amp over the factory 45 Amp. and have a pile of 40 Amp rated relays to install to improve the distribution of power much as Nacho's outlined but even running bone stock with just the Denso added everything is fine. (The Denso uses the 70 up style "external" voltage regulator.) I'll never draw 65 amp much less 120 so that issue will never matter.     

[Pete in NH]

I agree with Neal that an ammeter does provide much more useful information than a voltmeter. I've always found it helpful to know about the relative amounts of current flowing into or out of the battery. As Neal mentions if you're keeping a watchful eye on things you're okay. I do think for those that tend not to be as watchful and on top of things a voltmeter is safer with a big alternator.

[flyinlow]

I miss the ammeter too. Voltmeter now. Unless you upgraded to a shunt style ammeter and replaced the wiring , I would go the voltmeter route. I use a 100 amp Jegs (delco) single wire alt.  Runs dual fans , brighter headlights and OD trans. with no problems.

The area of concerned many have stated is a full charging condition. Very low battery, you jump the car and decide to let the alternator recharge the battery as you drive. 140 amps x 14 volts is almost 2000 watts going thru your bulkhead connectors and old ammeter. 

[b5blue]

  Re-charging a badly discharged battery with any car is a huge risk and a big no no. You can melt the insulation inside the wrapped bundling cross feeding to anything. The result could be run away charging or any manor of high risk of fire/problems later. I use to maintain my brother's construction equipment and they ruined his personal Ford Van by repeatedly charging the dump truck's battery when I was out of town. (The van had so many failures in other parts of the harness it was a nightmare and basically killed what was a really nice high end truck.)
  I have 2 friends, one owns a battery shop, the other re-manufactures alternators and generators and both were consulted about this poor idle output issue. (They are both experts in marine/auto and industrial power systems and both agree...no car/truck was EVER intended to be used to recharge a battery for more than the discharge from starting the engine.) You start getting into things like computing the RPMs of different Alt's pulley sizes to try and figure low speed or minimum output, fitment and such. They would have helped build up something but in the end the Denso worked out and we all agreed to try it. (Trust me I've watched it like a Hawk!)
  A single wire alt. is self exciting and output must be wired to the battery. That would mean all output goes to the battery first then to the harness.(That is how GM intended and engineered for.) Our cars were designed to be supplied power from the alternators output, the battery just starts the engine. Unless you modify the wiring you would be "back-feeding" power to the entire car through a wire intended to just top off the charge used for starting the engine. The load on the harness would appear to it as if you had no alt. at all, just a battery. (You could be drawing a constant load through a wire sized for a short term use of 10-20 amps.)
  Heat a wire and it will increase resistance, greater resistance results in more heat as the flow of electrons move through it. This stresses all connections as they expand and contract and the insulation tempers, becoming brittle or hard from the repeated baking. It's a run away effect that makes it's self worse as it progresses. I'm not trying to push the Denso on anyone, it was all I could find that matched my needs. (It does look kinda tiny sitting there on my 440.  )     

[flyinlow]

It is always best to recharge a dead battery first, before driving.

The only drawback I find with the single wire alternator is you can't put a switch on the field wires to turn the alternator off at the drag strip. Charging wires of an alternator are always hot. I run a #8 double insulated wire from my alternator to the charging post where the original battery was. The optima is in the trunk ,a double insulated 1 gauge feed goes to the charging post. The wire that used to go from the alternator to the ammeter goes to the starter relay thru a fusible link. The original battery feed goes to the starter relay thru its fusible link. .A double insulated # 10 wire feeds power from the charging post to the starter relay. My headlights ,MSD box and cooling fans run thru relays feed thru the battery fuse block I added near the charging post. The amount of power going inside my Charger is much smaller than when it was stock There is an additional battery fuse block in the trunk to feed the power seats, alarm, trunk lighting, etc. The negative battery cable in the trunk has a switch for conveinece and a 200 amp fuse to protect the whole electrical system. The headlights have there own grounds to the battery in case the main fuse blows while driving at night. Never has. Not a simple mod, but the car 's electrical system is more like a modern car and works very well.  

[b5blue]

I'd like to see pics if possible, that would help others. Did you tie into the original harness's Alt output wire somewhere?   
  When I bought my car it had been a drag only car for 8 years. One of the things done to it was battery in the trunk and at some point the positive cable grounded roasting the dash harness. The reason I got a good deal on it was the gauge cluster was in the trunk and a used replacement dash harness was installed just enough to get it back to racing. (Nobody wanted to buy it and sort all that out.) The first thing I had to do was buy an FSM and learn 70 Charger wiring inside and out to get everything working proper again. (18 years ago.)
  Regardless of what type Alt he installs the added high draw items should have there feeds run separate, fused and not part of original factory harness. A fused terminal block would be ideal. 

[Nacho-RT74]

I see the issue with big alternators as if there is ever a demand for all those amps they will be available and flow somewhere. That I think is the trouble spot. Yes, if the present load requirements are only 30 or 40 amps that is all the alternator will source. However, if the battery is really down or a short circuit develops somewhere, That big alternator will pump out more current than the wiring or particularly the ammeter can deal with safely.

totally agree BUT big alternators won't be ever a problem as far they feed the car at iddle, since batt will never get sucked, and even with stock 40-60 amps ammeters, the load won't go through if car doesn't require more power than the alternator sources.

only problem you can get is if your battery die, and if so, battery must be recharged out of the car... OR just at iddle on car ( I did it twice and everything worked as good or even better than expected )... never rev' it up.

[Ghoste]

Which brings up an interesting observation (to me anyway).  When we put a charger on our car in the garage most people know its best to use a trickle charger and bring the battery up slowly yet these same people if they get a boost in a parking lot or similar situation, the first thing they do when the car starts is hold it at a high rpm to charge the battery as quickly as they can. 

[flyinlow]

How does alternator charge the battery? The battery is at say 12.2 volts after starting the engine. The regulator wants the alternator to produce lets say 14.2 volts so you have 2.0 volts of "electrical pressure" to push electrons into the battery. How much amperage can you move with two volts differential? Depends on the resistance of the cables and battery itself. Most low battery's  that make your starter chatter still have 10-11.8 volts. A totally flat or damaged battery could accept a very high current I would think.

Maybe an Electrical Engineer can reply here.

[Pete in NH]

Hi,

Yes, a badly discharged battery will look like a very low resistance and will accept very high charge currents limited mainly by the alternators current output limit and as you suggest the resistance of the wiring between the alternator and the battery. The internal resistance of the battery is very, very low and is called source impedance. A good battery has no problem delivering 100 to 200 amps to a starter. So, by Ohm's law the source impedance is less than 12 volts/ 200 amps or .06 ohms. So, think of the current that can flow being driven by that 2 volt difference. Current = volts (2)/ ohms (.06) or potentially 33 amps. but, remember we only think the battery's source impedance is .06 ohms based on it delivering 200 amps to the starter when in fact it can be far lower. A good battery may be able to deliver  more than several thousand amps briefly into a dead short. Of course in the process the battery will likely really damage itself internally but it will try to source the current. A discharged battery will easily accept charging currents of 60 or more amps. but, again such high charging currents are not good for it. Automotive starting batteries are not made of solid lead plates but rather lead compounds pressed into a grid structure. High currents either in or out of the battery tends to knock the lead material out of the grid structure and down to the bottom of the cell housing where they will eventually short out the cell.