Are there any 140 amp alternators that will swap in place of the 100 amp Bosch unit? I have tried one 100A Bosch with external adjustable voltage regulator, one 100A Bosch with internal regulator, and one 100A denso. They were all about the same -- insufficient at low rpm. I am running a powerful electric engine fan and a special heated wide band 02 sensor and I have an underdrive crank pulley (but have raised my idle speed by 20% to 1000 rpm). I think I need an alternator that puts out more amps at low rpm. I am guessing that a 140 amp would put out about 40% more amps at low rpm, like idle speed, and would probably be sufficient.

Whatever will fit a B230FT in a 7 series is fine. It can be Bosch, Denso, or whatever. Any recommendations?

Thanks,

Philip Bradley

Phil,

Not sure you are at the root of your problem. It is not likely that a 140 amp alternator will have 40% more output at lower RPM. This is a max rating and it means that the copper windings in the alternator are larger diameter wire and the diodes can handle this current.

Start by looking for voltage drops in the system.

Measure the voltage from the negative battery terminal to the body of the alternator. This is about 0.1 Volts on my '89 760. If larger than this, I would suspect a poor groung. You may want to increase the diameter of the alternator ground cable as a matter of course with your larger current load.

Measure the voltage drop from the alternator output terminal to the battery positive terminal. I found this voltage drop to be about 0.15 volts on my car, and again I would be suspicious of the wiring if it was much greater than this.

Measure the voltage at the battery terminals at idle with the headlights on low. This should be 14 Volts minimum. If below this value, increase the engine speed to 2,000 / 2,500 rpm and see if the voltage meets this spec.

When taking these measurements, make sure your voltmeter is connected to the battery terminals and not the cable clamps on the battery terminals. These connections can have high resistance. You don't want to ignore the voltage drop this resistance would create.

I am not familiar with the external voltage regulators, but it may be possible to run sense wires directly to the battery terminals. Voltage regulators work by "sensing" a voltage. When it gets to the proper level, the current in the field winding of the alternator is removed which removes the magnetic field and therefore no more alternator output. On a conventional alternator, the volage is sensed at the output of the alternator. Any contact and cable resistance causes a drop in the voltage available to the battery. Check to see if your external regulator has sense terminals.

If you don't have a digital meter, please go buy one. They are inexpensive and invaluabe to any electrical work.

Post back with the results of these tests.

Dan

Thanks for the reply. I have already redone all the battery and main electrical wiring including grounds, all with marine grade larger gauge cable. I reduced voltage drop from about 1/2 volt to about .05 volts in the main electrical wiring. The stuff in the car is stock so drop gets worse. But the fan is wired to the battery through a relay.

If you have a fan that pulls 30 amps and it runs at idle if the temp is right, you need a spare 30 amps at idle. An alternator does not put out full amperage at idle. I need one that puts out more amps at idle than a 100A unit. Again, I have tried three different 100A units. All work the same. I have tried them all in another 745T as well and they work fine in it (it does not have a lot of extra accessories).

Philip Bradley

Get a different fan, if yours draws 30 amps.
I've got a Perma-Cool that draws less than 10 amps and is quite adequate.
As Dan says, a 140 amp alternator isn't going to make much difference at idle.
--
Jim McDonald

What is the voltage at idle? If voltage is normal (over 14V) a higher amp alternator will accomplish nothing. Heated O2 sensor uses insignificant power, I doubt that high power fan is using that much power. Headlights probably use more power.
Is your battery getting run down?
--
David Hunter

Thanks for the reply. The fan can draw 30 amps. I am not sure I have that to spare at idle with a 30 amp alternator. The battery does start to draw down. It is an Odyssey and is small and has little reserve time. My headlights are 60 watts each. Divided by a conservative 12, that would be 5 amps each, or 10 total on low beam. Add in the little lights and maybe there is 5 amps more, for a total of 15, or half what the fan can pull. With the high beams on as well, I might get close to the max amps the fan can pull. The 02 sensor is a wideband and is heated to 900 degrees C full time. WB02 work differently from NB02. I have not measured the draw, but I am sure it is a few more amps.

Philip Bradley

had a guy come into the shop with a hopped up mustang, he had put aftermarket pullys on his motor to get a wopping extra 2 hp, but it changed the ratio on the alternator pully that the regulator wouldnt even kick in, even after putting a hopped up (dont remember the make) high output alteranator on it. i dont know if you have messed with the pullys on your vehicle, that previous guy spent 500$ on his rod and still had to put his old ugly pullys back on.
you may investigate weather there is a smaller pully for your existing alternator before making a big jump in watts or dollars.
mike
--
mike, 1988 Volvo 240DL 114k , , previous 79 & 81 Volvo 244s

Thanks for the reply. The underdrive crank pulley is by Unorthrodox Racing. Most of the benefit comes from the approximately 6 lbs that is taken off the front of the crank, sort of like a lighter flywheel on the other end of the engine. The underdrive is about 20%. Stock idle speed is 750 rpm. I run more than 20% over that (20% would be 900 rpm). I run 1000 rpm idle. Unless my math is way off, I have compensated for the underdrive.

The alternator pulley is pretty small. I doubt there is a smaller one, but I will look into it. I may have to run a less powerful fan. I have been running the same pulley for over a year and this problem developed only after I swapped in a more powerful fan, added the WB02 sensor with the full time heating element and reduced the temp of the fan switch.

I may have to reverse some of those mods, but was hoping a high amp alternator would solve the problem.

Philip Bradley

An electric fan from a '94-95 940 pulls a lot less than 30 amps and has a 2-stage energy conserving power module to prevent the voltage drop you find when adding high current draw components. And it is used with a 100 amp alternator. I would get the fan and relay module from a 940 from the boneyard like I did for $25.
It shouldn't be this difficult. Also get the origional pulley on there, the added voltage for cooling is well worth the loss of a hp.
I am actually considering putting the engine mounted fan back on with the electric fan as an over-temp, A/C cooling. The motor is subject to catastrophic failure if that elec fan goes out, and on a turbo, it is not worth toasting the turbo, too. IIRC, the OEM Volvo engines with a completely electric set-up were the 940 n/a, NEVER on a turbo.
--
'89 245 Sportwagon, '04 V70 2.5T Sportwagon

Your pulley is 20% under WHAT??
Diameter?
Drive ratio of 6 inch crank to 3 inch alternator would be 2:1. 5 in to 3 in is 1.66:1, which is a bigger change in rpm than 20% If you changed the water pump pulley also it enters into the equation. Check your math (exact diameters) or just replace with the original pulley.
--
'89 245 Sportwagon, '04 V70 2.5T Sportwagon