Leroy Somer alternators are one of the most widely used generator alternator brands worldwide, and the two parts that fail most often on them are the automatic voltage regulator (AVR) and the rotating diode assembly. Both are precise electronic matches to a specific alternator model, so getting the exact part number right matters more here than with most mechanical parts. This guide covers how to identify the right AVR or diode kit for your alternator, and how to make sure what you order is genuine.
What does the AVR actually do?
The automatic voltage regulator senses your alternator’s output and adjusts the excitation current to keep voltage stable as load changes. A failing AVR is one of the most common reasons a generator’s output voltage drifts, surges, or drops out entirely under load — often before any mechanical fault shows up.
Leroy Somer AVR models
Each Leroy Somer alternator range is matched to a specific AVR model — the two aren’t interchangeable across ranges, so confirming the exact model printed on your existing AVR (or on your alternator’s dataplate) is essential:
- AVR R150 Leroy Somer
- AVR R449 Leroy Somer
- AVR R438 Leroy Somer
- AVR R250 Leroy Somer
- AVR R220 Leroy Somer
- AVR R120 Leroy Somer
- AVR D350 Leroy Somer
Diode assembly kits
The rotating diode assembly converts AC to DC to power the alternator’s exciter field. A failed diode is a common cause of low or no output, and like the AVR, the diode kit is matched to your specific alternator model:
- Leroy Somer Diode Assembly Kit ALT432KD001
- Leroy Somer Diode Assembly Kit ALT411KD001
- Leroy Somer Diode Assembly Kit 0004659918
Individual link diodes are also available if only one side of the bridge has failed: Genpac D82PFR80-1321 Link Diode (Negative) and the matching Genpac D82PF80-1320 Link Diode (Positive).
Browse the full range: Leroy Somer parts.
How to identify the right AVR or diode kit
- Check the part number printed on your existing AVR or diode kit. This is the fastest and most reliable way to confirm an exact replacement, since Leroy Somer AVR and diode models aren’t interchangeable across alternator ranges.
- If the old part is unreadable or missing, check your alternator’s dataplate. The alternator model and serial number let us cross-reference the correct AVR and diode kit for your specific unit.
- When in doubt, ask before ordering. Send us the alternator model or a photo of the part number and we’ll confirm the correct match before you buy.
Genuine parts vs. aftermarket
AVRs and diode assemblies are precision electronic components, not simple mechanical wear parts — an incorrect or out-of-spec AVR can cause voltage instability that damages connected equipment, not just the alternator itself. This is one area where confirming an exact, correct-model match matters more than choosing between genuine and aftermarket brands.
FAQ
How do I know which Leroy Somer AVR I need?
Check the model number printed directly on your existing AVR (e.g. R150, R449, R438, R250, R220, R120, or D350) — each is matched to a specific Leroy Somer alternator range and isn’t interchangeable with the others.
What are the symptoms of a failing AVR?
Unstable, surging, or drifting voltage output, especially under changing load, is the most common sign. In more severe failures, the alternator may produce no output at all.
What does a diode assembly kit do?
It converts AC to DC to power the alternator’s exciter field. A failed diode typically causes low or no alternator output, and is matched to your specific alternator model just like the AVR.
Can I replace just one diode instead of the whole kit?
Yes — individual positive and negative link diodes are available separately if only one side of the bridge has failed, rather than replacing the full assembly.
Where can I buy genuine Leroy Somer alternator parts online?
Ghaddar Machinery Co. stocks Leroy Somer AVRs across the R150, R449, R438, R250, R220, R120, and D350 ranges, plus matched diode assembly kits and individual link diodes.
Need help identifying a part?
Send us your alternator model or a photo of the part number on your existing AVR or diode kit and we’ll confirm the exact match before you order — Contact Ghaddar Machinery Co.
