Information on an AFS-70 Alternator Filter Surge Protector

[jssailem]

I'm planning the refit of my electrical systems. In looking at the lines form the alternator I find the positive lead runs from the alternator to the subject part - an alternator filter. The alternator for my Perkins 4107 diesel is a "DelcoRemy". Looks like a truck alternator. Best guess is it is regulated and from the late 70's. The wires to the filter appear 10awg. Filter has connections - Batt - Grnd - Alt.

When I examine the wiring designs for Alternator/Battery charging systems this appears to be an unneeded part.
Not needed remove? Or Keep?

 

[Hartley]

The purpose of an alternator filter is to remove the whining or whistling noise produced by the alternator on the DC buss, which can show up in the audio of VHF radios, stereos, etc. The PO who put it in probably did so for that reason, and the ancient alternator may be why. While the wiring (#10) seems a bit small for the job, the filter may, in fact, be doing some good for you. To find out for sure, short the "alt" terminal to the "batt" terminal when the engine is running, the battery is charging and see if noise appears in the radio or stereo speakers (while they are in use, of course).

73 DE Hartley
S/V Atsa

 

[jssailem]

Thanks DE. That helps.

 

[Maine Sail]

Get rid of it!! These are a band-aid approach and cause additional voltage drop in the charging circuit. If they fail they can also take out your alternator. I have a video, somewhere on my hard drive, of a boat that had been chewing through battery banks yearly. At a mere 31A of charge current he had 0.6V of voltage drop in the positive cable. The 80A noise filter was responsible for .2V of that at just 31A. In the negative cable he had .58V of drop. At a 14.6V regulated voltage his batteries were seeing only 13.42V with less than 1/3 of his rated alternator output flowing......

In an ideal world your alternator circuit, + & -, would have no more than about 0.1V to 0.2V of total circuit voltage drop at close to rated outpu,t or a volt sensing circuit to compensate.. Your wires are not going to yield this.

The safest location for a noise-filter is in the circuit that feeds the affected electronics.

 

[jssailem]

Thank you for the clear response Maine. Needed that help to clarify the issue. We are fortunate to have your participation in the forum.

 

[Ned Ludd]

Reviving this post...Just finished my stereo install, unit has a filter & fuse on the power in line. The charging system is a 1976 era (newer than that but same design) 1 wire 35 amp alternator. Alt out goes to ammeter then to starter, then 1/both/2 switch, upgrading this is on the list. If the power is on to the stereo and engine is running I get an awful growl (not AC hiss) through the speakers, even when volume control is at zero. On just battery it is awesome. Following advise here I have converted to 1 bank for all loads and the second for emergency starting, cleaned up 3 engine grounding locations to a single point and cleaned up a bunch of misc bad practice electrical work. What have I missed?