Power Factor and George Marsh

Hey there George, instead of experimenting (but hey thats half the fun right, I'm an experimenter myself) and guessing as to how much capacitance needed to improve on a motors power factor, if you Google something like capacitors to improve AC motor power factor, you will get a gazillion hits of pages that actually have tables and formulas to compute the sizes needed, but that takes away all the fun grrrrrrrr lol

By the way, if you add too much capacitance it looks like theres a risk of damage YIKES !!! and I saw some figures that a goal of 95% is about all you want to go for.

A capacitor isnt any magic elixir or energy source, its a passive non 100% efficient series device that in itself has some losses (it cant produce any energy, it uses some). It can, if needed, improve power factor by counter acting some of the motors inductance by adding capacitance so the current comes back in phase with the voltage (just as if a pure resistive load with no L or C).

If the PF is lousy, the utility or genny must pump out the VECTOR SUM of the two currents, that in phase plus that out of phase, and many utilities charge you extra for that capacity. The motor uses only X amount of energy to do its actual work (spin the shaft under load) while all that out of phase ringing is wasted as heat mostly. Still if the PF is bad the utility or genny has to produce true work energy (to spin the shaft) plus that which gets wasted as heat.....

It would be fun if your experimented capacitance value corresponds to what the charts show is needed!!!!!!!!!

Have fun, keep safe, keep us posted, dont get hold of a charged up big capacitor OUCH lol

Mark in Michigan, you out there? Whatcha think??

John T (Remember Im rusty on this so no warranty and dont have a calf if this isnt perfect!!!)

John T,
I have purchased a cheap PF meter on ebay. The boat from china is running a little slow. I was concerned about going too far, that's why I stopped at 170 uf. However each time I added capacitors, the total current went down. To play it safe, I installed a 10 amp fuse on the capacitor side. Fuse hasn't blown yet. Put in a metal electrical box, which of course was FREE. I got my education from Redneck Teck where we were taught to do things on the cheap. My first course was B&D, short for Bungie cord and duct tape. I didn't realize the infinate number of ways you can use B&D.

Ok, back on track. In the early 80's my dad had a heart attach, I got stuck wiring up 2 phase converter for a goverment contract. My dad was the sub-contractor doing the electrical. We had two 25 hp pumps to wire up. There was no circuit diagram to work off of, I had to make one in my head. I drew the blue prints later. They wanted the pump on the left to fire up first and after a short delay, the pump on the right. Next time it was to be reversed, right then left. We had just a few days to get the job done or the fine would have been out of sight, and the fine may have killed my father . Perhaps that's why my dad had a heart attach in the first place, all the stress. Long story short, there was a rule of thumb for static phase converters. So many farads/hp for the start capacitors and so many for the run capacitors. I remember getting special parts flown in over night and working almost 48 hours without sleep. We had a 400 amp service to work with. Thank God I had two brothers to assist with the big wires and the load center. We completed the job with about 2 hours to spare. After starting the pumps we played around with the run caps to get the current balanced the best you can on all three legs. It made the the goverment officials happy. They were ther with their cameras breathing down are necks. I never heard back from the contractor, so we must have done something right. BTW, the two 55 mic 440 volt caps I used were left overs from that job.

Thanks for the info. I'll keep you posted as to what I find out, unless someone knows what the rule of thumb is. I only plan to use my genny when I have a power outage, which may be the next ice storm or strong wind. Had both in the past 2 years and without power for about a week or more each time. Also use to power up my 4 peak hp chainsaw, which the owner's manual says the genny shouldn't be connect to saws. Apparently the genny doesn't like universal motors.

Sorry I'm so long winded. Perhaps I should put a warning on my post, long winded. You may not want to read.

Isn't life good in your retirement years?

George

JohnT,

Here is an interesting read about power factoring fractional hp motors.


I come to know that we can reduce our electical bill if we add Capasitor at home."

This is a lie, do not believe it! Improving Power Factor only saves MONEY, not energy, and only if your utility assesses a penalty for having poor Power Factor. The vast majority of utilities only assess PF penalties to their larger industrial users, not residential users. it takes a special meter to even see poor PF, and that meter is more expensive than the tiny amount of revenue the utility can recover by installing and maintaining them on every residence. Even if you are assessed a penalty, improving PF on a load as tiny as 3.5kW will not likely be worth the cost of installing a capacitor.


But do not believe the lies about saving energy, it is just not true. CURRENT is reduced, but current is not energy, it is only a component of energy. When you tally all of the factors into how you are charged for energy, improving PF makes no difference to you, the user and bill payer.

George