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Discuss Will isolation transformer absorb in rush current and not the generator in the Electrical Forum area at ElectriciansForums.net

Megawatt

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USA Advisor
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I have a 10,000 watt surge and 7000 watt running capacity on a 240/120 vac generator. Now this is a theory I have electric heat with 10,000 watt heating elements. When the heating elements kick on it bogs down the generator to the point I have to kill the heat. The question is if I bought a 15 kva isolation transformer 240/120 primary and 240/120 secondary and installed it between my main panel and the generator does anyone think the generator would absorb the inrush current and not the generator so bad. Again I haven’t done it but I’m curious
 
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James the Spark1976

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Esteemed Member
Your problem is an undersized generator.
10kw surge is only for starting motors etc.
If you have 10kw of heating you will need a 10kw running capacity generator at the minimum.

I would not recommend going below a 12kw generator as you should leave a bit in reserve and not run it flat out for long periods.
An isolation transformer will make the problem worse, not better as you will get transformer losses added to the load so it will use more power.
 

Megawatt

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USA Advisor
  • Thread Starter Thread Starter
  • #3
I have a 10,000 watt surge and 7000 watt running capacity on a 240/120 vac generator. Now this is a theory I have electric heat with 10,000 watt heating elements. When the heating elements kick on it bogs down the generator to the point I have to kill the heat. The question is if I bought a 15 kva isolation transformer 240/120 primary and 240/120 secondary and installed it between my main panel and the generator does anyone think the generator would absorb the inrush current and not the generator so bad. Again I haven’t done it but I’m curious
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Dan could change the spelling on the word it should be absorb not adorn I know it’s a spell check error on the transformer question thanks
Dan could you take the USA of my thread I want to know what you guys think
Your problem is an undersized generator.
10kw surge is only for starting motors etc.
If you have 10kw of heating you will need a 10kw running capacity generator at the minimum.

I would not recommend going below a 12kw generator as you should leave a bit in reserve and not run it flat out for long periods.
An isolation transformer will make the problem worse, not better as you will get transformer losses added to the load so it will use more power.
thats what I’m looking for what people think iv got to agree thanks
 

Megawatt

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USA Advisor
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  • #5
What do you mean take the USA off your thread?
I wanted y’alls input and with that being there looked like if was for the USA people. To be honest I haven’t been impressed with what I’ve read and I’ll leave it at that
Post automatically merged:

I wanted y’alls input and with that being there looked like if was for the USA people. To be honest I haven’t been impressed with what I’ve read and I’ll leave it at that
I’m referring to Americans who I have not been impressed
 

Rob

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Arms Access
A resistive load of heating elements will not have in rush current. Unless it's some form of induction heating, arc furness etc...

The generator is simply undersized. You want to aim the normal load to be 80% of the generators rating.

Avoid prolonged periods of running the generator below 50% of its rated output, this really only applies to diesel generators, as the engine (motor is I think the US term) will soot up and it'll die pretty quickly.
 

Wilko

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Arms Access
Hi - my thought is the isolating transformer will not absorb the attached load inrush current. It will do its best to mirror the secondary load on the primary side.
 

Lucien Nunes

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TA
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Esteemed Member
It's not so much inrush that's causing the problem, it's that the generator is too small. Is it really 7kW rated or 7kVA? Because a commercial 7kVA genny may only have enough engine power for 5.6kW. The load pf is assumed to be 0.8 to make the rating look bigger, whereas your pf is unity demanding the full 10kW or a minimum 12.5kVA rating.
 

Megawatt

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USA Advisor
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  • #9
It's not so much inrush that's causing the problem, it's that the generator is too small. Is it really 7kW rated or 7kVA? Because a commercial 7kVA genny may only have enough engine power for 5.6kW. The load pf is assumed to be 0.8 to make the rating look bigger, whereas your pf is unity demanding the full 10kW or a minimum 12.5kVA rating.
It’s a 10kva surge and 7kva running the bad thing is it just has a 30 amp twist lock 240ac receptacle and 2 20amp receptacles but I got a great buy and that’s why I’m asking y’all what yalls input would be, it will run my whole house with the exception that I cut off hot water heater, tumble dryer. I’m just trying new things. The heat kicks in and the current spikes at 74 amps thanks for your input
 

TonyMitchell

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Arms Access
When specifying a standby generator, your first decision is to choose between,
  1. a set that can support the full load of the board/s, i.e. rated similar to the DNO incomer, OR
  2. a smaller set that can support essential services
For industrial/commercial purposes, option 1 is the norm.
For residential purposes, option 2 is often preferable, giving backup with a little sacrifice, i.e. you can still turn all the lights on, watch TV, boil a kettle, use a microwave, run a gas/oil fired heating installation, open the garage doors & gates. The sacrifice may be you can't use the oven, hob, washing machine, tumble dryer & air conditioning, during an DNO outage, the benefit is you're not running a larger set with a comparatively tiny load most of the time.

This is different to when specifying event (temporary power) generator/s, where you may or may not be able to apply diversity and face other challenges such as balancing very variable loads across three phases.
 

Dan

Admin
Staff member
Dan could you take the USA of my thread I want to know what you guys think

thats what I’m looking for what people think iv got to agree thanks
What do you mean take the USA off your thread?
Done.

It was a prefix matey. We can click edit from the drop down in the moderators options above the first post, and change it to select 'No Prefix' right at the bottom of the list.

Also fixed typo / spell check change in title. :)
 

Megawatt

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USA Advisor
  • Thread Starter Thread Starter
  • #12
When specifying a standby generator, your first decision is to choose between,
  1. a set that can support the full load of the board/s, i.e. rated similar to the DNO incomer, OR
  2. a smaller set that can support essential services
For industrial/commercial purposes, option 1 is the norm.
For residential purposes, option 2 is often preferable, giving backup with a little sacrifice, i.e. you can still turn all the lights on, watch TV, boil a kettle, use a microwave, run a gas/oil fired heating installation, open the garage doors & gates. The sacrifice may be you can't use the oven, hob, washing machine, tumble dryer & air conditioning, during an DNO outage, the benefit is you're not running a larger set with a comparatively tiny load most of the time.

This is different to when specifying event (temporary power) generator/s, where you may or may not be able to apply diversity and face other challenges such as balancing very variable loads across three phases.
It’s not 3 phase and I can still run my oven, water heater, well, air conditioner and dryer but not at the same time, I just cut off what I don’t need. I just can’t run my heat
 

TonyMitchell

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Arms Access
It’s not 3 phase and I can still run my oven, water heater, well, air conditioner and dryer but not at the same time, I just cut off what I don’t need. I just can’t run my heat
My post was intended to be generic, not specific to your situation. More about choosing the size of set.
 

Megawatt

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USA Advisor
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  • #14
Done.

It was a prefix matey. We can click edit from the drop down in the moderators options above the first post, and change it to select 'No Prefix' right at the bottom of the list.

Also fixed typo / spell check change in title. :)
Thanks Dan
My post was intended to be generic, not specific to your situation. More about choosing the size of set.
i know it’s to small but I got it so cheap, that’s why I’m trying to figure out what I can do and can’t do thanks for your input

My next option is to see if the elements in my heat are 1 10,000 watt element or 2 - 5000 watt elements and just take one element out of service
 
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