ST head - safety factor (or not)

[veggie]

Some heads are rated with "intermittent" and "continuous" ratings (Eg: 6000 watt intermittent, 5000w continuous).

Can my ST-5 put out 5kw on a continuous basis.?
Can it do more for very short periods.
Anyone out there pulling the max from an ST head for long periods of time?

Cheers,
Veggie

[mobile_bob]

i suspect that most of the good heads will deliver full capacity in kwatts into a unity powerfactor load
on a continous basis, of course most folks don't have a purely resistive/unity powerfactor load.

so maybe you derate to 75-80% of nameplate kwatts and you should be fine for continous duty
on the average residential installation that has the typical powerfactor or maybe .8??

time to go recruiting an EE to answer this one,, i will see what i can find out.

bob g

[Ronmar]

Well not having a power plant capable of sustaining that much load, I only have my powers of observation to rely upon.  Compared to a box store 5KW generator, I would call the ST-5 overbuilt.  I am pretty sure My ST-5 generator head weighs more than an entire 5KW gas genset at the local box store.  It has more iron and more copper.  It is physically larger and has a larger blower.  Most of this of course is because of the 4 generator poles of a 1800 RPM head vs a 2 pole 3600 RPM head.  Since you can't buy a 1800 RPM gas generator down at the box store, this is a very apples to oranges comparison.

One thing the added size gives you which is a big plus with load is additional heat dissipation surface area.  I think they all have the copper to get the job done, but in the end I would imagine it would come down to who can sustain the heat dissipation of that rated load...

I would say you can probably hang 5KW on a ST-5 till the cows get tired and come home, and that heavy core and copper will give you a substantial overload/starting capacity. 

My .02   

[Henry W]

Hello Veggie,

The ST gen-heads are pretty tough. My ST-12 has unbelievable surge capability. I would imagine that the ST-5 has good surge capability also. It would be at a smaller scale than the ST-12 but very impressive for a 5K.

You need to get a load on it and let all of us know how it works.

Henry

[TimSR2]

 I have load tested my ST5 with a 4800watt construction heater plus all the lights in my shop for 4 hour burns with no ill effect. I think the 5000 watt rating is continuous.

Tim

[mobile_bob]

i am trying to get an answer that i understand enough to pass on 

basically the st head can pull 5kwatts continously driving a resistive (unity power factor) load

what i am not sure of is the derate for driving a non linear (lagging powerfactor) load such as might be
typical in a home with electric motors, fl lights, well pump, and older puters etc. which might put the system's
pf something other than unity.

My friend the EE is a very busy man, i sent an email and got a response, but am unclear about one aspect
of his answer so i wanna clear it up before stating anything.

having said all that, maybe the 5kwatt head is good at 5kwatt continously provided the field current stay's under the
nameplate rating? the field might be the weakest link and if it burns out your done.

bob g

[mobile_bob]

ok, i think now i have this right and this is what it boils down to

i asked this question to a good friend who is an EE, an avid diy'er and author
and he should also be a teacher or professor (as we call him) because of his
incredible ability to teach.

the st head is rated for a unity power factor or resistive load, so
a 5kwatt st head will deliver 5000watts into a purely resistive load only...

in a load that has a lagging powerfactor its capacity will have to be derated if it
is to live.

in some cases it may only deliver 3500watts continously, so

the only way to know for sure is to monitor the field current while driving your intended load
if you exceed the nameplate field current you better back off or you risk damaging the head.

he relates to me that one should monitor both the field current and the stator current while driving
the intended load, and if either is exceeded the load must be reduced.

bottom line, a st5 will run incandesant lightbulbs, resistance heaters or powerfactor corrected appliances up to near its full 5kwatt rating, but

anything under a unity powerfactor and the head will need to be derated.

so one should be concerned with powerfactor in his system and take measures to correct it where possible or live with a reduced generator capacity.

thanks to my as of yet unnamed EE friend, who maybe i can get to join up when he has more time?

bob g

[Henry W]

So it looks like I made the right decision getting an ST-12 for my S195 powered gen-set.

Henry

[mobile_bob]

Henry:

it certainly looks that way to me too,

my st7.5 might be a bit light for my end use, so i may well
put either my st12 or my stc12 on my 195changfa

probably the stc because i have a nice square d breaker panel loaded full of breakers
already and i have some 3 phase equipment for my shop,

with the larger genhead the genset will then be engine limited and not genhead limited
so when it gets to full rack you are done.

bob g

[Henry W]

At 7680 Watts my voltage only drops to 239 volts. Hertz stays at 58-59. I say that is pretty good.

Bob I think we are on to somthing here.

Henry

[Henry W]

I googled unity power factor and here is one of many I came up with.

http://en.wikipedia.org/wiki/Power_factor

This will be a good Topic to work and understand.

Henry

[veggie]

Bob,

Thanks for taking the time to get that information.
With so many ST head users on this forum, that info is very useful.

I would assume that all the 6/1 listeroid owners running ST5 heads are ok for the same reasons as hwew.
The 6/1 engine will hit max BHP at around 4kw (depending on elevation) so kw output is limited by the engine.

Cheers,
Veggie

[mobile_bob]

factoring in drive losses, generator efficiency and a few other factors
of lessor amounts the 6/1 is typically doing well to produce 3-3.5kwatts
electrical out of any genhead into a resistive load.

so couple with a st5 the 3500watts output pretty much is a match for
the generators ability to supply power to an average powerfactor load
of maybe .8 or so.

so you would likely blow black smoke out of the exhaust just before black smoke
came out of the generator. (continuous operation assumed)

or so i think

bob g

[bschwartz]

I have an ST-5 from Tom Osborne right now, and I'm going to order one of his PM heads to play with.  He has (among others) a 3.5K head, and a 6.5K head.  I've got a 6/1, so by what I'm reading here I should go with the 6.5K head to build in a safety factor.  Thoughts before I call Tom to order?