2JZFC

iTrader: (26)

I know there have been endless threads on this topic but none appears to address the issue I want to solve: voltage drop at high RPM/full load.

I am using a DR44G, single wire with the resistor and a 4g cable going back to the batt side of the cut-off switch. 14.2-14.4V at cold startup and 13.6-13.8V normal driving and the occasional hit. That would be considered normal, however, when making a pass, as RPMs/Load increases, the voltage starts dropping, sometimes down 13.1V. So, for the guys that drag race and spin their engines past 6,500, are you monitoring batt voltage? If you don't have this issue, can you detail your charging setup. I tend to believe the issue is RPM related, i.e, alternator RPM. I've read that alternators do not work well at 17K RPM and above. For me, with an ATI balancer and a 2.4" alternator pulley, that would be around 6,000 engine RPMs and that's right about where my voltage starts to drop and at 7,000, the alternator is spinning right at 20K RPMs. Soon as the RPMs drop, the voltage comes right back up. With a 145A alternator and the cooling fan shutting off at 75% TPS, I wouldn't think 2 FPs, an alky pump, running lights and whatever the engine needs would put such a load on the charging system.

I've read a lot about the alternator output curve but it all seems to be focused on AMPs at idle and low RPMs. Is there a way to make an OEM alternator maintain voltage at high speed?

Pop N Wood

iTrader: (1)

Switching to a 3 wire set up will better regulate voltage. Also connect the output side of the alternator to the fuse box and not the battery. Batteries can draw so much current the alternator will never be able to affect the voltage at the loads. Not a popular opinion around here but fact non the less.

http://www.madelectrical.com/electri...esensing.shtml


145 Amp alternator is actually too big for what you need.

Forcefed86

iTrader: (4)

I have my 160A 1 wire alternator wired directly to the bus first, then back to the battery in the trunk on my mustang. With a sightly larger pulley (not 100% sure on diameter) It does the exact same thing. Previously ran a 100a (1 wire self exciting deal) alternator and voltage would drop into the 12's. The 160A alternator maintains low 13's above 6k or so and a steady 14.3 or so at idle and cruise. Both of my LS cars acted the exact same. FWIW my other car has the battery up front as well, so it's not a voltage drop across the wiring to the trunk.

Seems to me it's the nature of the alternator... I'd be curious if a larger pulley would cure it. I've also tried the "Caspers Voltage Booster" It is supposed to bump voltage through the sensing wire at WOT. It did absolutely nothing for either of my cars.

2JZFC

iTrader: (26)

Glad to see I'm not the only one. Read a tech article that stated a 10% drop in voltage results to about a 30% performance drop in electrical components, especially coil-driven components such as pumps and injectors. We know what a BAP does to a FP and this is the opposite effect. Ironically, I would bet a lot of folks don't realize they have this issue.

Not surprised the Casper's didn't work. You and I come from the Buick world and know that's where Casper's market focus was and those V-6s were hard-pressed to see much pass 5,500 , so no problem there. If it is indeed an alternator high-RPM issue, then a bigger alt pulley could be the ticket. For me, a 3" alt pulley would spin the alt right at about 16K at 7K engine RPMs. Ironically, a lot of the performance alternator vendors like Powermaster recommend a 2:1 crank to alt ratio but none of them list an alt pulley bigger 2.4". The other option is the 5.67" super damper @ $370 and salvage what I can get out of the one I have, but then I would have to be concerned about the WP ratio, yada, yada.

Waiting for a call back from Powermaster to see if they have a 3" pulley. Maybe there is a LS1techer reading this that does CNC and can punch out a couple for us.

Forcefed86

iTrader: (4)

Wish i would paid more attention. Initially I ran the SFI speedmaster under drive dampner. But I didnt like the idea of underdriving the water pump and switched to an OEM f-body shortly after. Your welcome to it if u pay shipping. I'm curious if that fixes it.

pdxmotorhead

I've tried both output of the ALT to the battery and the circuit block, I like it to the battery "+" cable.
most auto circuits are not built to handle much over 50 or 60 amps continuous, so going to the circuit block
causes a voltage drop between the alt and battery,, kinda what your trying to avoid.

A standard car battery can deliver a hundred or more amps for minutes, a parallel battery set is even higher,
a pair of 450CCA batteries can outperform a 1050CCA battery in many conditions..
A heavy ignition system at full rpm you can be pulling > 70A on a street car, a big full race CDI setup can
pull well over 100A at 6000 rpm's, I think in a lot of cases its more about a whole system than just the alternator or
ecu or whatever.. I always upgrade the alt charge wire to 8 or 6 gauge just to reduce resistance and heating,
the battery to circuit block gets it as well. Then if there is a intermediate/main fuse box I upgrade the cable from
the circuit block to the intermediate/main fuse block to at least a 8 or 10... Then upsize the fuel pump wire and the
main feed to the ECU and the TCM. Lower resistance is always good in my opinion..

Forcefed86

iTrader: (4)

I run the Odyssey PC925 battery on both my setups. I wonder if a better battery would soak up some of the load. I’ve got a spare little PC680 I could wire up in parallel just to see if it makes a difference. Or maybe temporarily toss a standard large battery in the rear.

I still feel like it’s just the nature of the alternator. Does anyone have logs if their setup not behaving like this at RPM?

Project GatTagO

iTrader: (7)

Are you all wiring the alternator S terminal to the main power distribution point of the electrical system?

Andrew

pdxmotorhead

If you look at the switching spec of most of the diodes in the alternators, they are tough,
but not terribly fast, than multiply the RPM*the number of windings and the frequency
your asking that rectifier/bridge to deal with is fairly impressive.. There are some 16V
Alternators just for the purpose of boosting higher voltage but I've never needed one..

What I'm now wondering, is what is the real concern that is being chased, if its that the
voltmeter drops on a 1/4 mile run,, don't sweat it, its normal electrical physics, if its that
the voltage is staying low ,, while driving around,, thats an issue. 14.6 it a fairly healthy number
once you go under 14 its getting sketchy..

One of the reasons dragsters and sprint cars use magnetos.. Spark gets hotter with RPM,, to a point.. LOL

One way to go is buy a big LI battery if your losing too much power on a run..
They will hold the current at max for a while..

Forcefed86

iTrader: (4)

Mine are both self exciting deals. No sensing wire. Should maintain a set voltage the entire rpm range I'd think.

Project GatTagO

iTrader: (7)

The L terminal is what "excites" the alternator. The S (sense) terminal is what let's the alternator know that there is a voltage drop at the main power distribution point, so the alternator can compensate for the voltage drop.
On my GTO I only have the L terminal connected. When the cooling fans kick on, there is a pretty good voltage drop that is clearly visible on the volt meter. On my Cougar, I have both the L and the S terminals wired, and the system voltage is much more stable and generally never drops below 14v.

Andrew

2JZFC

iTrader: (26)

Andrew, just running a single wire with the resistor to pin L. Spoke with Powermaster and the tech said the issue we're dealing with is that the brushes are bouncing at such high rpms, sort of like valve float.

Project GatTagO

iTrader: (7)

Scotty,

​​​​Honestly, that sounds like BS to me. Try adding a wire to the S terminal. It should go from the S pin on the 4 prong connector to the main power distribution point, wherever that is in your system. The terminals for the alternator connector are Metripack 150 series. I'm pretty sure I have a bunch and would gladly throw a few in an envelope headed your way.

Andrew

Forcefed86

iTrader: (4)

There is a lot of info out there on the brush bouncing issue. It’s especially bad on reman. units since the QC is way down. I don’t think it’s BS.

I believe the 1-wire deals have a set charging rate as they supply a constant resisted voltage to the sensing terminal. So they “should” remain pretty solid the entire RPM range.... But mine doesn't.

FWIW originally I ran an OEM F-body alternator with the sensing wire hooked directly to my fan circuit. This did fix the voltage drop issue when I kicked the fan on at idle/cruise. But it made no difference at high RPM. I even went as far as to setup a boost activated switch that would supply 5v to the sensing wire while in boost to try and “bump” the charging rate. Again this worked when switched at idle and cruise... not at high RPM.

After my OEM 100a Fbody alternator died I had a hell of a time finding anything that would keep voltage above 12 at RPM. None of the parts store reman 100a were up to the task. (I know some of the larger truck alts do) These smaller Fbody 160A 1 wire deals at least keep voltage in the 13’s. MUCH better than the remains at around the same price. Think I paid $140 shipped.

2JZFC

iTrader: (26)

I just read the "Alternator Bible" and having the S pin wired up makes sense, but as Forcefed said, it doesn't address the high RPM issue.

Here is a quote directly from the Alternator Bible:
"............we have to be careful not to use such a small pulley that at high engine rpm we exceed the alternator's maximum rpm. For example, it's no use installing a 3x overdrive pulley on an alternator installed in a race car that runs all day at 7000 engine rpm - because the alternator will be spinning at 3 x 7000 = 21,000 rpm!

Fortunately, race car's spend little time at idle and even when they do their electrical demands are low (no a/c, stereo, electric windows, etc.) so they can operate with high-ratio (low numerical) alternator pulleys."

BINGO!! This is exactly what we are experiencing. I have the 2.4" pulley, but just found a 2.75" made by ASP and Texas Speed has them in stock for $32.95. So, at 7,000 engine RPMs, this will put my alternator speed at a tick over 17K which on paper, should help. Shouldn't have any issue at idle as my engine idles at 1,000. Once I get the suspension fixed, I'm going to hook up the S wire and try this pulley.

Forcefed86

iTrader: (4)

Wonder how the spacing would be on something like these 3" 6-rib pulleys...Doesn't state it's 17mm shaft diameter either but I'm guessing they are pretty universal?

https://www.jegs.com/i/March-Performance/655/120-08/10002/-1?CAWELAID=230006180000158416&CAGPSPN=pla&CAAGID=4 4693592161&CATCI=pla-191844202151&CATARGETID=230006180039217633&cadevic e=c&gclid=EAIaIQobChMIpNDqxuGM2wIVBtbACh1OtA6cEAQY AyABEgI9ZvD_BwE

stevieturbo

Alternators not charging at higher rpm seems to be a very common problem and there have been multiple threads over the years.

And I've been a victim of it myself...but no solution as such. One unit was a cheapy replacement...I think it was around 6k it would just simply stop charging.

The other time it happened was a GM unit that had been repaired a couple of times, after the last repair at a local alternator place....it too stopped charging after 6k. I did try new brushes myself after this...made no difference.
I did also then buy a new voltage regulator etc for it and fit it, but at the same time also bought another unit, 170A from these guys but also with a slightly larger pulley.

https://alternatorparts.com/ad230-ad...ternators.html

It's been fine for a few years now. So never got around to re-trying the one I fitted a new reg to....and hopefully I wont need to lol

hookemdevils22

iTrader: (12)

Andrew, my LQ4 (105 amp) alternator came with only the L terminal wired in. Care to speculate as to why the General would omit what appears to be a fairly important component of the charging logic?

My voltage drops a fair bit with AC and fan on, so I'll be adding this into my harness to see if it helps before digging in further.

Project GatTagO

iTrader: (7)

I don't have a good answer for that. On my first LS swap (back in 2002 into a RX7) I used a stock 4th gen Camaro harness. It too only had the L terminal wired to the ECU. On my GTO, I have the GMPP harness with the e67 ECU, and it too only has the L terminal wired to the ECU. I can't say what the charging behavior was like on the RX7, because I never really paid any attention. I really noticed it on my GTO, as I have a big volt meter as part of my gauge cluster, and I have already said what it tends to do.

While building my Cougar I read up on modern alternators, and the common takeaway was that wiring the S terminal properly tends to improve the performance of the overall electrical system. Given that knowledge I wanted to see what would happen, and as it turns out, it does indeed improve the overall performance of the electrical system.

Ultimately, GM has gone to a PWM control strategy for their alternators. The ECU senses voltage at some junction in the electrical system and sends the appropriate duty cycle command to the alternator to boost output as needed.

I just put a care package in the mail to 2JZFC and I am curious to see what happens as a result of him implementing the S terminal in his Mustang.

Andrew

Pop N Wood

iTrader: (1)

That is for gas mileage. Turn the alternator off when accelerating to decrease the engine load, then when decelerating pump extra current into the battery. Sort of a low capacity Prius.

And yes, a voltage sensing wire improves the voltage regulation of the whole system. 3 wire alternator