MEP-026C

First let me say what a great board this is! I've been looking for a forum like this for quite some time. Now here's my newbie question - I acquired a low time MEP-026C military genset, 3KW 28V DC output. As I look at the tech pubs I see lots of references to diodes, inverters and heat sinks. Could this mean that this unit is really an AC generator that then uses an inverter to make the output DC? If so, is it possible to remove the inverter from the circuit and extract AC current from the gen? All thoughts appreciated!

Thought I could have done a better job on the subj of my orig post. Here's my basic question: Does this genset produce 28 VDC direct from a DC generator or does it use an AC gen to produce AC current that is then rectified to DC? If it is an AC gen, then would it be possible to capture that AC current and use it to power AC motors, lghts, pumps, etc.? Thanx again for your thoughts.

It is probably irrelevant if it is an alternator or generator because the chance of it being a 60Hz single or 3 phase unit is remote, it could be a 6 phase high frequency unit; or some combination of Hz and phases that make good DC. It would probably be more reasonable to get a uninterruptible power supply (UPS) like used for computer backup power with batteries to get 60 hz power from your unit. Or you might purchase one of the CD manuals sold on E-bay and then you can determine exactly what you have and wither modifications can be made as you have outlined. It is a good exercise

RichMc

Generally, the best thing do do if you want A.C is to run the output through an inverter. The inverter converts from D.C to A.C, not vice versa. You will normally find, and someone may correct me on this, that an A.C generator uses slip rings for the rotor outputs, and the D.C generator will have brushes and commutators. The rectifier packs are mainly just to smooth the D.C output.

Hope this helps,

Matt

DC generators and AC alternators both generate AC voltage and current. The DC generator contains a high speed mechanical switch consisting of a comutator and brushes to convert the AC into rippling DC for the output. The AC alternator does not need the switching so just has slip rings instead of segments like the commutator. If DC is desired out of the alternator, such as in automotive use, then a rectifier assembly is used to convert the AC into rippling DC. In both cases the rippling is the result of imperfect switching/rectification of the AC voltage/current.

Well put Max. I must admit I was a tad vague on the original description. That's what happens when trying to concentrate on two things at once:-) An A.C generator/alternator using slip rings can work for either A.C, or D.C with the addition of a bridge rectifier assembly, whereas the D.C generator can only output D.C due to the brush/segment design. This is roughly how I meant the original post to sound.

All the best,

Matt

In an alternator, the slip-rings aren't on the main output...they're for the field winding on the rotor.

The main alternator windings are in the stator (fixed, non-rotating, outer portion).

Sorry, I don't have an answer to the original question. I've used that rig in the field many times, to charge 24v batts in heavy equipment; but never poked around inside one.

An electricity beginner is not well served by this thread. Not everything or everyone is inaccurate, but which is which, huh? That's my 2 cents.

The replies are not meant to be definitive, but, at least they provide a starting point for the original question which should highlight which area he needs to find additional info on. I will concur, electricity and obscure information are a potentially lethal combination, but if Ken is going to be collecting generators, he will have to tackle this area at some point. As with anything, a good in depth book on the subject is the best way to go initially, but revision is easier if you know what to look for:-)

All the best in your new hobby Ken,

Matt

Wow! Thanx for all great responses and all the good info. I do have all the gov't tech pubs on this unit and with a little more basic knowledge I'll be dangerous. Your notes of caution are well received and rest assured, I have a healthy respect for electricity. Thanx again and I'll keep you advised as I continue to experiment with this unit. All the best K. Graeser

It is most difficult for any author to cover everything right off in the first writing. Everyone thinks differently and interprets data in different ways. Eventually someone comes across the right things to say about some particular subject and it all eventually falls into place. It becomes an "I thought you said this, but I now see that you meant that. Oh so that makes a difference and knowing that now, here is the way we should look at it.'

I thought it was helpful bringing different experiances into the discussion. It all sorts out in the end with all the experianced knowledgable folks who regularily check in here at Harry's engine site.

Getting back to your original question: The MEP26 - Is that the gasoline set powered by the 4 cylinder opposed engine? If it's the one that is, then it's definitely a 60Hz, 3 phase (delta) alternator feeding a full wave rectifier bridge. I had one that I hooked up to some BIG step-up transformers to get 120/208 3 phase. The 1.5kW 28V DC set was a bit different - it used a 5 phase alternator!

Just to point out, there was another mistake in my original post as Richard pointed out. 'A.C generator uses slip rings for the rotor outputs' should have read 'rotor inputs', as the rotor is usually the field, being supplied with a low voltage rectified D.C input. If I was as eloquent as Russ, my fingers might one day type what my brain is thinking:-) If this post sounds like gobbledegook, I give up:-)

MEP-026C is indeed powered by a 4 cyl, horiz opposed, gas engine (4AO32 is designation, I believe). Thanx for the tip.

[19shell68]

Did you ever get 120/208 volt, 60 hz from your MEP-026C generator?