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Compass Marine How To | all galleries >> Welcome To >> LiFePO4 Batteries - Thoughts & Musings > Cooked Stator
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Cooked Stator

This is exactly what happens when you don't current limit an alternator that will be feeding an LFP bank. It will literally cook itself. Here the magnet wire coating has literally been cooked right off the stator windings. This happened on an AGM bank and this was a factory dumb regulated alternator with no built-in thermal compensation..

USE A BALMAR MC-614 regulator, and current limit the alt, if you have an LFP bank!!!

RPM, Engine Room Temp & Current Limiting:

What does low engine RPM have to do with alternator heat? Many sailors and cruisers want to charge at low RPM while on the hook. Today's high performance alternators can put out a substantial portion of their total output at just a fast engine idle. This is good as it keeps your neighbors happier in the anchorage..

But wait, there is a catch, always is.. The problem with low RPM charging is that with a fast idle we have very slow alternator fan speeds. The speed of the rotor actually keeps the alternator cool.

The most abusive loads for a high performance alternator are not at cruise RPM, they are usually at fast idle! Keep in mind many of the new small case alternators can handle 17,000 - 19,000 shaft RPM. This creates excellent cooling but we never get there on most cruising boats.

Because of this the alt is best set up and hot-load tested to fast idle RPM. This is where it will get the hottest.

Alternator Set Up & Load Testing:

It is not just good enough to program the regulator and walk away. Every alternator will respond differently to the field wire from the regulator. Proper set up will lead to a long alternator life and an alternator that can survive the abuse an LFP bank throws at it.

How do I do this? It is not difficult.

You will need the following:

#1 An on-board inverter capable of exceeding the alternators current capability, usually 2000W or more, or a portable inverter capable of at least 2000W or more.

#2 A good restive AC load such as a heat gun, hair dryer or portable heater. If the alternator and inverter are large enough you may need two of these devices.

#3 A remote temperature sensor attached to the alternator case that can be read with the engine room 100% closed up and sealed tight. Most DVM's offer a remote temp probe.

Hot load testing and set up:

Step #1 - Connect temp sensor to alt and close engine room

Step #2 - Run the boat under load, with the inverter loaded down, and at cruise RPM for at least 30 minutes

Step #3 - Return to dock or mooring and leave the motor running at fast idle

Step #4 - Keep inverter/AC load running. This load should be in excess of alternators capability.

Step #5 - Monitor alternator temp, does temp exceed 225F?

Step #6 - If so, adjust Balmar Belt Manager to level #1

Step #7 - Continue load testing and monitor temp, did the alt still go over 225F?

Step #8 - If so move to Belt Manager Level #2

Continue this process until the alternator stays below 225F loaded to max output.

TIP: I start at Belt Manager Level #4 and work my way up. Most alts require level #3 or #4.

NOTE: Balmar's Belt Manger used to be called Amp Manger in previous regulators. It is the feature you use to current limit your alternator and prevent it from cooking itself.

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