Load checking a generator?

Cole2534 · Jun 11, 2019

Figured this would go best here.

Is there a good way to impose a load on a generator? I have the instruments to test it's output, just need to create a demand.

A hair dryer would maybe work for a small unit?

Rob F. · Jun 11, 2019

What size genny? I run my 5500 honda hooked up to my electric water heater to put close to max load on it. I want to remember the two heater elements are 4500 each. You can change the elements for different wattage.

Cole2534 · Jun 11, 2019

The purpose of this is should I find a suitable generator used I'd like to check it before I buy it, so I'd like something portable.

Currently I'm wanting small like a Honda inverter type, so 2-4kw would be a good range.

Ziggy2 · Jun 11, 2019

Cole2534 said:
The purpose of this is should I find a suitable generator used I'd like to check it before I buy it, so I'd like something portable.

Currently I'm wanting small like a Honda inverter type, so 2-4kw would be a good range.

The newer generators usually either work or they don't. Almost anything could be used for a load.

A skill saw is pretty good in that it has a significant starting load and can have a decent sized run load if you are cutting a board. Not very scientific but will give you the desired data.

Rob F. · Jun 11, 2019

Electric heaters, add as many as you need to to get your load. Skillsaw cutting a heavy cut would be OK for a 2kw.

gustafson · Jun 11, 2019

My electric chainsaw pops the breaker on my 3kwish generator reliably, so power tools have a high enough startup load to be useful

electric heaters can be 1500 watts so good for steady state test

Cole2534 · Jun 11, 2019

Rob F. said:
Electric heaters, add as many as you need to to get your load. Skillsaw cutting a heavy cut would be OK for a 2kw.

Skill saw and a 4x4 should be perfect. Thanks!

bloomautomatic · Jun 11, 2019

electric motors will have an inrush current that spikes the power up. a power tool will test if it can keep up.

A heater is resistive and will draw the same current at start-up as it does when it's running.

Take both when you test it.

Rob F. · Jun 11, 2019

And remember when using the saw that you are trying to stall the saw, not make a clean cut. Test it with wall power to get a feel for what it takes to stall it. (if it will) A dull blade would be a good thing for testing load.

Big B · Jun 11, 2019

The Honda inverter generators are very good quality but when they say 2,000 watt they mean 2,000 watt surge and 1,600 continuous so don't be fooled by the rating. Most generators will have a claimed output printed on the side of them and the surge will be significantly higher. I also have a generac 4,000 watt generator that is a 6,250 surge rate.

I have used my Honda EU2000I inverter generator to charge my battery bank on our fifth wheel and can adjust the charge rate up to 150 amps 12 volt. The Killawatt meter that I plug into the generator to monitor load will sometimes show in the 1,800 or 1,900 continuous load and not trip the breaker.

thermite · Jun 11, 2019

Cole2534 said:
The purpose of this is should I find a suitable generator used I'd like to check it before I buy it, so I'd like something portable.

Currently I'm wanting small like a Honda inverter type, so 2-4kw would be a good range.

More than one hair-dryer or electric coffee/teapot, then.

I'd just use a two-element electric "hotplate" I have handy.

Smaller than the average space heater, less messy than cutting wood at some other Pilgrim's place of business!

BTW - if/as/when you look at larger capacity gen set:

- water heaters are usually arranged so only one of the two elements can be on at a time, AND those elements will rapidly degrade if NOT immersed in water, so not a great solution, "loose".

- Better to use an electric range/oven - or its spare/replacement stovetop "burner" elements. Cheap enough. Easily paralleled if you need multiples.

My largest is a 9 KW "home canning" element - good fit to testing ACTUAL load (about 7 KW) my nominal 10 KW MEP-803a is called on even for "whole house" use - including winter electric heat or summertime A/C.

"Success" when living off a gen set has a great deal to do with "timing" the loads - manually if not automatically.

We (most folks) are happy to trim our consumption during power-outages anyway. Simple stuff such as not trying to bake a turkey, take hot showers, run the washer and dryer all at the same time, etc.

2CW

Cole2534 · Jun 11, 2019

Big B said:
The Honda inverter generators are very good quality but when they say 2,000 watt they mean 2,000 watt surge and 1,600 continuous so don't be fooled by the rating. Most generators will have a claimed output printed on the side of them and the surge will be significantly higher. I also have a generac 4,000 watt generator that is a 6,250 surge rate.

I have used my Honda EU2000I inverter generator to charge my battery bank on our fifth wheel and can adjust the charge rate up to 150 amps 12 volt. The Killawatt meter that I plug into the generator to monitor load will sometimes show in the 1,800 or 1,900 continuous load and not trip the breaker.

Are doing this directly with the inverter, or are you using a charger plugged into it? I'm intrigued about the former option.

thermite · Jun 11, 2019

Cole2534 said:
Are doing this directly with the inverter, or are you using a charger plugged into it? I'm intrigued about the former option.

With charger(s) is a pretty safe guess.

The specs are widely published on that model. The 12V "direct" outlet is rated for 8 Amps.

huleo · Jun 11, 2019

Easiest reliable test loads are cooking range heating elements. They come in various sizes, but you need to apply OHMs law if you will apply a different voltage to it. However, once plugged in, because a resistive load will have a PF=1, you can test the loaded voltage and test amperage to determine watts.

I have built a load bank with these and some switches to change load conditions. Get 3-5 in various sizes and you can play with the load conditions.

warning! Keep in mind a resistive element will NOT maintain resistance as it heats so you can NOT just measure resistance cold and assume the value. Resistance will increase with heat and that is exactly how elements are designed so they don't burn up. The hotter they get, the higher the resistance so they hit a point of equilibrium.

thermite · Jun 11, 2019

huleo said:
Easiest reliable test loads are cooking range heating elements.

Cheap, too. About nine bucks, up as replacements, "loose".

Mind - may make more sense to own a hotplate or two. Already wired and cased, and one can use such for a lot more than just testing a gen set!

Now - with Diesels, as my one is, it is very bad cess to run them unloaded, so I need the 9 KW element just to keep my periodic readiness test runs from "wet stacking" the lovely "tactical quiet" -ized Lister-Petter four-banger Diesel.

huleo · Jun 11, 2019

Uh, that price can get right down to FREE if you go steal them from old ranges. I like to have the dedicated 240V "tester", but can run 120V at 1/4 of the power.

thermite · Jun 11, 2019

huleo said:
Uh, that price can get right down to FREE if you go steal them from old ranges. I like to have the dedicated 240V "tester", but can run 120V at 1/4 of the power.

"Convenience issue" as to even finding donor ranges. We aren't able to scavenge or purchase at either the County-run landfill OR the local metals recycler - a situation more common each year, nationwide, what with liability inch-hoorances, atc.

I found that 9 KW solid-top "canning" element on EBay as NOS for a planned use with wife & M'in-law's bigger Woks. Never got it installed.

Added gas cooktops that could (also) handle the "round bottom" Woks instead.

And.. cross-off one more load on the gen set if/as/when.

JST · Jun 11, 2019

Load checking depends on what you want to test.

most folks will just want to check power, and that is fine, load up with heaters to full power and see.

A handy sort of heater load for larger increments is the heater blocks for electric home heat. They do need a fan to run at full power, which is usually 5 kW per block for the ones we had access to, but they can be used at lower power on convection alone. Some have a thermal switch to prevent overheating.

One of our clients at a previous employer had a generator load trailer for checking Boeing 707 aircraft generators and electrical systems. It had the ability to connect different load resistors, in a step sequence from very low to full load. But it also had the ability to connect inductors to change the power factor. many generators are spec'd at 0.8 PF, so the current may be measured suitable for 10kVA, and the "real" power might be 8kW.

Most will not need to worry about that, but it is worth knowing. That 707 load bank was rated at something like 180 kW, if I recall correctly. Do not remember the kVA.

Load checking a generator?

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