Ignoramus22022 wrote:
On Thu, 24 Nov 2005 01:04:56 GMT, Pete C. wrote:
Ignoramus22022 wrote:
On Wed, 23 Nov 2005 23:21:02 GMT, Bruce L Bergman wrote:
On Wed, 23 Nov 2005 16:22:24 GMT, Ignoramus22022
wrote:
On Wed, 23 Nov 2005 16:13:58 GMT, Bruce L Bergman wrote:
On Wed, 23 Nov 2005 wrote:
On Tue, 22 Nov 2005 12:55:29 -0800, "Bob Headrick" wrote:
"Highland Ham" wrote:
Bob , Interesting info ; can you confirm that the 18 pcs 12V battery were
in fact 9 strings of 2 batts in series (each string having a fuse )
providing 24 V ? or were all the 18 batts in parallel ?
Actually they were all in series, making it a bit nerve-wracking to replace a
battery in the string.
216 volt battery pack??? I don't think so.
No, quite possible and makes some design sense - they would not need
a heavy output transformer in the unit boosting the voltage of a 36V
or 48V battery string after converting it to a sine wave AC, as 216V
would be right around the sine wave peak voltage of 120VAC. Just run
the battery DC through two sets of power transistors to let through a
reconstituted sine wave - one for the positive half of the output
waveform, the other negative.
And it cuts the current the transistors have to pass.
Bruce, this also sounds like a simple approach to generating 3 phase
out of DC. Without the noise and weight of rotary phase
converters. What are your thoughts on that?
Quite Plausible, but when you add the caveat of reproducing 3-Phase
power the engineering just got really complicated, and more than
likely rather expensive. And I'm NOT a high-powered electronics drive
wonk by any means, the best I could do for fixing them is look for the
obviously crispy components and swap out the blown boards - or swap
the crispy parts and diodes that fail a VOM test and see if that does
it.
With a single phase inverter, they're just doing a push-pull on one
240V lead, relative to the center tapped neutral.
Right. As you know, I recently made a DC - AC inverter myself.
When you try 3-phase, there's going to be constant voltage, current
and capacitance interaction between all three sets of "hot AC"
switching transistors (or Triacs, or whatever). And the load's
resistive, inductive and capacitive components are all going to come
into play.
Yep.
The resulting inverter would need to be built rather robust, and be
able to overcome drive issues with brute force where finesse won't do.
Compared to that, RPC's are the KISS method. And RPC's aren't a bad
way to go, if they are well balanced and have cooling air you can tuck
them away in a closet.
You are right. I am going to redo my RPC into a 17.5 HP RPC. (two
motors, 10 and 7.5 HP). Right now I have a 10 HP RPC.
Someone offered me a Semikron 6 IGBT drive, with which I could make a
3 phase inverter. That sort of made me interested.
i
Get your hands on a large, like 30kw or better, used as in "please take
it out of here", three phase, online UPS from a computer room
installation. As long as you can supply adequate power to the DC bus the
inverter portion will happily generate your three phase power with no
issues with designing and inverter or trying to synchronize three
inverters or duty cycle problems. It's a DC - 3 phase AC continuous duty
inverter, ready-to-go.
A 30 kVa UPS would weigh approximately a ton. That's without
batteries. It is beyond what I can handle.
No way, I put in a 30kw 3 phase UPS (Best Unity/1) and it was close to a
ton with batteries. Without batteries (when I moved it across a raised
floor with a pallet jack) it was far under a ton.
Since it needs a system for producing DC, it would be comparable to
what the UPS already has.
It has a system for producing DC, it's just setup for three phase input.
Depending on how it is configured it could be quite easy to rework the
input section for single phase. The more modular the design the better
and you might get lucky and find three discrete DC supplies, one fed
from each phase, that couldn't care less if they were actually 120
degrees apart.
That means that I would have a monster that weighs a ton.
That would mean you have all the clean sine wave three phase power your
shop could need, uninterruptable no less, and heat for the winter.
I almost bought a 15 kVa UPS though.
i
The building I used to work in had about six monster UPSes in the
basement, each feeding a 600A 208/120V 3 phase buss duct running up
through the building to multiple PDUs. They had the nice 5 gal size
glass cased batteries in the strings. Also had five 800KW diesel
generators with paralleling switch gear and 40,000 gal of fuel supply.
Redundant utility feeds as well. Place would have made a nice house if
it was in a better location
Pete C.