External Rectifiers
If your looking for an External Rectifier, give us a call to see if we're the right fit for you.
ALL POWERLINE alternators are designed to withstand extreme temperatures from -40°F to +250°F environments from our smallest 120 amp to our largest 275 amp rating. An external rectifier is NOT necessary with any POWERLINE alternator, as we use half inch press fit 70 amp, 400 volt rated diodes in all models of our alternators. Where necessary, we have added additional diodes working in parallel to handle the current and extreme heat. Our alternators have the following diode configurations:
23HD - 120A - Six 70 Amp (3 Positive, 3 Negative)
24HD - 100A, 160A, 190A, 220A - Twelve 70 Amp (6 Positive, 6 Negative)
25HD - 100A, 160A, 190A, - Twelve 70 Amp (6 Positive, 6 Negative)
25HD - 200A, 220A, 250A, 275A - Twenty Four 70 Amp (12 Positive, 12 Negative)
28HD - 180A, Eight 70 Amp (4 Positive, 4 Negative)
31HD - 150A, 160A, 200A, 250A - Twelve 70 Amp (6 Positive, 6 Negative)
ABOUT EXTERNAL RECTIFIERS
Certain older Emergency vehicles were built with the alternator mounted in a very tight area of the engine compartment and very close to a large turbocharger with extremely hot air entering the rear of the alternator. At that point in time, the largest press fit diodes available were rated at 50 amps maximum, and the alternators on those vehicles only had a total of 6 internal diodes. The internal diodes could easily be exposed to 325°F! When exposed to that heat, they would fail, so in order to keep the alternator alive and maintain the highest possible output and long life performance, an external rectifier and a external regulator was the best choice for those vehicles.
HD Power Solutions manufactures three heavy duty replacement external rectifiers for ambulance and fire truck applications.
- Model # 33-56 @ 220 Amps
- Model # 33-59 @ 275 Amps
- Model # 33-77 @ 350 Amps
All 3 models are a direct replacement for the Leece Neville "1111CA" external rectifier. (Leece Neville no longer manufacturers the external 1111CA rectifier)
Almost all of today's alternators have internal rectifiers and regulators from the result of great thermal dissipation improvements in diode current ratings and heat sink design over the years, with the exception being some emergency vehicles that have an extremely high under hood temperature near the alternator's rear air inlet. In those cases, it becomes necessary to definitely use an external rectifier and regulator for maximum alternator life and performance.
The internal rectifier (which normally consists of a total of 6 diodes, 3 positive and 3 negative) converts the alternating current (AC) from the alternator's stator windings to direct current (DC). This rectification is necessary as a battery can only be charged with DC. If you try to charge a battery (DC) with alternating current (AC), you will destroy the battery! But all rectifiers have limitations to both heat and current that is passing through them. If the temperature exceeds the thermal rating of the silicon diodes, they will be destroyed just the same as if they are passing way more electrical current that they are rated for. All semiconductors have a thermal curve. As the temperature increases, the internal resistance between the silicon junction decreases, so the example below shows the maximum current ratings that a heavy duty 50 amp press fit alternator power diode can withstand without failing.
Just the small amount of 36°F (2°C) will be the difference of life or death of the diodes if they are not protected from the excess heat! A few alternators have internal regulators that can shut down the alternator at 289°F (142°C) (This protects the diodes from failure, but this also means that when the shutdown occurs you are running only on battery power until the temperature entering the alternator drops below 280°F!) Without a temperature controlled regulator, the alternator has no way stopping the diode meltdown as its only job is to provide all the power to operate the vehicles loads and maintain a fully charged battery as well. This is why an external rectifier and external regulator was chosen for continuous full output and survival of the alternator on these emergency vehicles.
