Harbor Freight 7200W Gen head

[pigseye]

All,
What do you think of the 7200W gen head on sale at HF on sale for $279?  Find a 20% off coupon and get this head for $223.00.

http://www.harborfreightusa.com/usa/itemdisplay/displayItem.do?itemid=45416

Except for the 3600rpm, it looks like it would be a god place to start for a novice.

Thoughts?
Pigseye

[jimmer]

I'm not looking for a gen head, but where are these 20% off coupons?

jim

[sid]

check their web page//they usually have some unadvertised specials//sid

[solarguy]

For occasional use, it's probably fine.  It's probably as good as the gen head on a homeowner duty generator from one of the big box stores.  For all I know, it's the same factory.

However...

For heavy duty, mission critical use, I am extremely hesitant to put that much faith in HF.

If I'm wrong, you spend some extra dough on a heavier head that's easier to service.  If you're "wrong", you end up unable to milk the cows or operate the iron lung for the wife or something else when it really really matters.

Yes, I freely admit that I tend to overbuild things.

On the other hand, I rarely have to make repairs.

Good luck and keep us posted either way!

troy

[Doug]

Pigseye:

Unlike IC engines the speed the head turns at is much less a factor in how long it last, bearings will fail thats about it. There's also an upside to running a two pole machine, a slight improvement in efficiency. With only two poles verses four in a 1800 rpm unit there is less leakage of the magnetic flux between poles. The ration of wire in the coil size is higher in a two pole machine so you have a little lower copper losses. For a given kVA rating of the machine you have less Iron and there for loses because the total amount of flux is halved because the rotor is spining at twice the speed( voltage induced in a coil is a function of speed and lines of flux cut by a conductor ).

All that said the difference in machines as small as we are dealing with here is hardly worth the trouble we loose more power to friction just trying to spin the heads then we would gain in efficiency. Two four pole not much of an issue if we had say six or eight pole machines this small then you would see some real differences. This is the primary reason you seldom see small at all.

Doug

[europachris]

Just for kicks today I had a quote done on a Marathon LIMA-MAC series 5kW 1800 rpm, 2 bearing, 4 wire 120/240 volt head.  This is a 150 pound beauty with a separate brushless exciter enclosed within the unit. 

Please be sitting down......




$1500 and some change.

I didn't call them back to see if this was a 'special' or what, as I'm sure they don't make as many 2-bearing heads vs. direct coupled, but WOW!!!  I'll ring them tomorrow and see if they can do any better, etc.

This is not quite comparable to a ST-5 head except in size/weight as it has a far superior separate brushless exciter and regulation.  But, even taking that out of the equation, the ST-5 head is a pretty darn good deal, as I'm sure we all know.

I would hazard a guess that the Lima-MAC head has a lot lower harmonic distortion than the ST-5.  I saw a o-scope trace of the 60Hz waveform out of a ST head and it was pretty darn ugly.  That said, I've not put my scope on my Markon BL105A 3.2kW 3600 rpm head yet.  It's a premium quality 'consumer' grade head, brushless 2-bearing.

Chris

[Doug]

Yup I would have to say counting the number of slots In pictures and looking at the rotor of an ST there is going to be some distortion but hey look at the price. On the up side induction motor loads especialy the kind with run capacitors will smooth off some of the rough edges. I haven't tried this but someone with a scope might want to see if adding some VA of capacitance to the generator and backing off the rotor exictation current helps, or it could just make the voltage regulation worse.
Hard to say looking at a vector diagram of the forces at play in a poly phase syncronous machine that doesn't use a harmonic winding to induce the excitation current is kind of like looking up the tail pipe of car and trying to guess what gasses come out of a horses ass...

Doug

[pigseye]

At $223 a piece a guy could buy 2 of them and keep one as a back up. 

But I bet the one time the genhead does fail, it will be 10:00pm at -30 degrees.  ;-)

[ixtow]

I'd get one just as a backup to run while I was rewinding or replacing brushes on a real gen head.

Or maybe becasue I'm too anxious to wait for an ST and want to break in my engine NOW!  ;-)

[Doug]

Looking at some pictures and the connection diagrams poste here. I think its safe to say there might even be a little room for improvement rewinding an ST. Loose the 50hz taps, up the wire and perhaps even remove the K winding or better yet adapt it to serve as a charging circut.
You can squeeze more power out for sure, but I'd be inclined to try and lower the Copper looses by packing the slots as tight with as many CMs per amp as possible.

This is a lot of screwing around for nothing I doubt you'll ever need to rewind one of these if you keep them clean and cool.

Doug

[mobile_bob]

Dad bought one of the harbor freight 3600 rpm heads, and is relatively pleased with it. but it is only used for intermittent service.

i would be concerned about the brgs used, and if i was to use one for main power source would probably replace them with the best i could find.

also i would limit the draw to 5kwatt continuous, and figure some way to shock mount it to keep away vibration if possible,

although i am not crazy myself with 3600 rpm, i guess if it has been balanced well maybe it would last.

another concern would be the driving mechanism, using a microgroove belt on a lister would get you up to speed, one also has to remember
to check the engineering charts on the amount of power a given groove count can stand using the quite small driven pulley diameter, you might have to step up to more grooves to pull the power "effectively" and perhaps more importantly "dependably".

just because a given belt is stated to be able to take a given hp, does not mean it will do so dependably in all applications, some apps such as such a large step up in speed greatly reduce the hp rating of a given belt.

such things as c/c distance, degree of contact, surge loads (such as a welder), and the fact that it will be driven by a single cylinder, can in some cases remove up to 50% (or more) percent of a given belt rating.

just some random thoughts and observations

bob g

[europachris]

just because a given belt is stated to be able to take a given hp, does not mean it will do so dependably in all applications, some apps such as such a large step up in speed greatly reduce the hp rating of a given belt.

such things as c/c distance, degree of contact, surge loads (such as a welder), and the fact that it will be driven by a single cylinder, can in some cases remove up to 50% (or more) percent of a given belt rating.

just some random thoughts and observations

bob g

Good points, Bob.  That's why I chose to go with "L" section, 6 rib belting on my setup.  Originally it was to be a 6/1 driving the 3.2KW 3600 rpm head, so I bought a 4.2" diameter Browning pulley and bushing.  That would have given the proper ratio.  The chart ratings were on the order of 5 or 6  horsepower PER RIB!  Plenty of margin to de-rate for the severe 'speed up' ratio and such.

I ended up running a Changfa R185 instead, so I went to an 8" pulley on the engine ($$$$) from Browning so I could keep the pulley on the generator.  It runs super smooth and quiet (although I can't hear much over the engine ) and I've pulled 5kW from the gen head trying to start my well pump and aside from really loading down the engine, the belt didn't slip or nuthin'.

I keep the tension as low as possible to help out the bearing life, but bearings on my head (Markon BL105) are standard sealed units available for just a few dollars each.  I'm not running off-grid, so I get very little use on my setup (outdoor projects or power failures) so I'll likely have my bearings fail due to old age and dry grease than by wearing them out.

Chris

[nutman]

I wonder if this head can be mounted vertically? I have an old vertical shaft motor just laying around taking up space.

Nutman

[lister-deaf]

HarborFrieght's Assembly and Operation instructions
click this
http://www.harborfreight.com/manuals/45000-45999/45416.pdf

what size do i need two puilleys for my 14/1,000 rpm 20 inches wheel or large pulley and pulley for generator head 3,600 rpm)?

[Andre Blanchard]

3600 / 1000 = 20 / X
  .
  .
  .
X = (1000 * 20) / 3600
X = 5.556