My MEP002A – MEP003A Batteries Are Not Recharging, Fuse Keeps Popping, Maybe Voltage Regulator or Stator is Bad. Help!

We get a number of inquires about the following on MEP002A and MEP003A units, but many other military units have similar setups and issues. Here are the symptoms:

• Dual 24v battery set up is not working. Batteries will not charge and/or are dying or dead.
• In-line fuse for battery charging system keeps popping out.
• Voltage regulator – rectifier for the battery charging system might not be working.
• Stator for the battery charging system might not be working.

Lots going on here. You should check the following before getting in deeper:

• Is the unit grounded properly?
• Are nuts, bolts, wires tight and in good condition all along path from stator to batteries?
• Are your batteries configured correctly for 24v setup with tight connections?

Let’s get deeper:

• Test the stator: Using a multi-meter test the stator- while unit is running @1800 rpm (=60 Hz) should be 33.1 volts. Not running 0.7 ohms continuity. This checks to make sure the stator is connected properly with no bad connections. That said, even if connections are good, when the unit is running, the increased voltage can cause problems with frayed wires or gunked up magnets or windings in the stator. If you want to be thorough, you should visually inspect the stator to ensure no rust, water damage or paint damage (CARC paint can get in strange places and destroy connections and continuity.) When running you should be somewhere in the neighborhood of 33 volts or so (with one meter lead on wire 1 and one on wire 2, set for AC volts). If you have 33 volts and the fuse and fuse holder are both good, then you have a bad VR. Testing the stator makes sure the diodes in the stator are working and that there are no bad connections (poor/missing continuity). The diodes are the main culprit if the stator is malfunctioning.
• Note: AC voltage comes out of the stator, but voltage at regulator, fuse and on lines to battery are all DC. So ensure your multi-meter is set correctly to AC or DC readings.
• Note: NEVER ever attach or detach wiring at the batteries while a unit is running. NEVER play with wires while unit is running. I can cause spikes in amperage and damage parts.
• Note: NEVER let the MEP002A and MEP003A units idle. Get them up to 1800 rpm (=60 Hz) immediately and set the unit there. The unit should always run at 1800 rpm (while warming up, running or cooling down, always 1800 rpm). If you idle the unit, damage to the main voltage regulator that controls generator output, can be damaged. If this occurs, GMG can repair your VR for less than $200 under most circumstances.
• Inspect the fuse holder and fuse: Make sure the fuse holder (look inside) is secure and not cracked. Ensure that the fuse is good as well. Check connections at fuse holder.
• Inspect voltage regulator: Check ground connection to frame. The VR itself should ground to frame if securely bolted on. Check voltage output from VR to batteries. Even with unit off, but batteries connected, you should see 24+ volts all along the path from VR to batteries. Ensure that every section is reading 24+ volt DC.  This is also checking for continuity and damaged wires along the route from VR to batteries.
  • Test DC voltage at the regulator wire that is marked with the red band. Should be around 24 to 24.5 volts DC.
  • If so, DO NOT disconnect anything and start the generator. Now measure for DC voltage at the regulator red banded wire again. This time it should be 26 to 28 volts DC give or take in order to charge the 24v battery system.
  • If it is, measure the DC voltage at the batteries positive and negative terminals. This voltage should be the same 26 to 28 Volts DC. If it is, then your charging system is working properly. So while running voltage is increased as amperage is stuffed into the batteries. While the unit is off, the batteries and system will read 24 volts +, but not as high as 26 – 28 volts.
• If the stator is bad, it must be removed and replaced or have the diodes fixed/replaced. This requires pulling the blower wheel off (not the flywheel). You will need a puller of sorts to do so.
• GMG can help supply any parts that you need (Voltage Regulator, Stator, Fuses)