Hello, collective mind...

My 1975 Volvo 245 (B20F engine) has mechanical fuel-injection (K-Jet) but Bosch electronic ignition.

That car normally uses a Bosch 55-Amps alternator with remote/external regulator.

That 55-Amps Alt. is now defective.

Can I use a Bosch 35-Amps alternator (given by a friend), from a Volvo 140, in it's place?

Will a 35-Amps work with the regulator of the 55-Amps?

Will that alternator be powerful enough?

My 245 has no radio, driving-lights or other 'extra' electrical equipment.

Big thanks in advance for your advice.

I think you'd be fine... best would be to put it in and test it with everything on... see if you are still getting positive amps going into the battery. Or if you know the loads each electrical unit draws, do the math.

Now all that said... I assume that 35 amp alternator is likely from a pre-injection car. '71 or older. Back then, it could be a Bosch or Motorola. Your voltage regulator may not be compatible with this older alternator... so check that first.

If you find that both are the Bosch type, maybe the brush pack from the earlier one is the same as what's in your '75... and that's usually all that goes wrong. Might just be able to swap that and go. If not the same, you could still just check the brushes in your 55A alternator... if they are worn out, you can just replace them and go...

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-Matt I ♥ my ♂

Thanks for your reply.

The problem with my 55A is that, at 3:00 AM in the dark, I installed a charger on my battery.

Unfortunately, I reversed polarities for a second and the alternator's diode-trio probably blew.

My 'ALT' warning-lamp glows with ignition 'off' and key 'out'.

I'll probably try to do the math for the current-draw, as you suggest.

If your 75 still has the factory single fuel pump, you MIGHT be ok. If you have the upgrade to twin pumps, probably not.

But on the first cold, rainy night, when you need the lights, wipers, and heater blower, you don't want to find out that 35A isn't enough...

My car does have the single fuel-pump.

Cold, rainy, snowy nights are to be expected for another month (or two), up here.

I guess I could just use the 35-A until I fix the 55A.

I am usually less-than-zero at understanding automotive-electricity.

I guess that, with lights, wipers and blower on, I could eventually find myself with a dead battery, even?

Thanks for your reply.

I guess I could just use the 35-A until I fix the 55A

Very short term. Get the 55A fixed or even upgrade to 70A for a bit of padding in alternator output.

I guess that, with lights, wipers and blower on, I could eventually find myself with a dead battery, even?

And the 35A alternator will be toast too. Too much demand on an alternator will cause it to run all the time, creating heat. The more demand, the more heat, the shorter lived the alternator. The battery will suffer from undercharge as it will be the reservoir supplying the needs of the various circuits that the alternator would normally supply. Worst case scenario would be dead battery and no way to recharge it until both alternator and battery are changed.

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Mr. Shannon DeWolfe -- (I've taken to using Mr. because my name tends to mislead folks on the WWW. I am a 52 year old fat man

Thanks for your enlightening reply.

I might use the 35A short-term until I fix the 55A myself, again...

I had already done so about 1 1/2 year ago for the exact same problem.

I'll also look into wether I could make a later 55A alternator, with integrated regulator, fit my B20 engine.

I have a few of those alternators.

Pierre,

If you replaced the battery a year ago and repaired the 55 at that time, you really should consider upgrading; apparently the 55A alternator is not keeping the battery topped up. A Delco single wire alternator will work fine with a bracket from SWEM or of your own design. You can go as big as you want. Given the battery history you just related, I would plus size by about 20 percent.

sd

SD,

I didn't replace the battery back then, just fixed the 55A alternator. The battery was still ok.

Now that you mention it, though, my symptoms are slightly different now from what they were then.

I'll have my battery checked this time, just in case.

I'll look into your Delco/SWEM/homemade-bracket suggestion.

Thanks.