Author Topic: Gifted Generator / House AC Tolerance  (Read 6213 times)

Spork

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Gifted Generator / House AC Tolerance
« on: October 15, 2015, 06:17:07 PM »

Long story short: One of my wife's friends got frustrated with their old, tired, non-starting generator and told her "Take that thing, it doesn't work."  There were multiple little easy problems with it that I worked through to get it running.

Now that it's running, I'm getting 107.5v/61hz out of it.  Now, I've never really played with generators, but I was expecting 120v.  Is 107v within tolerance of most of my home appliances?  Or is that going to be low enough to cause them harm? 

I'm pretty much a part swapper... Pulling out the voltage regulator board and troubleshooting that isn't in my skill set.  Pulling the board and ordering a new one is.

a1smith

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Re: Gifted Generator / House AC Tolerance
« Reply #1 on: October 15, 2015, 08:24:12 PM »
I think you should be fine for most AC loads.  Here are some special cases:

If a load wants to run at constant power and voltage is low the current will be proportionally higher which may cause more heating (e.g. motors) due to Joule heating (I^2*R losses).  So, just check those types of loads to make sure they don't overheat.

For loads using synchronous motors (anyone still have a AC powered clock with hour and minute hands?) they will run faster since you have 61 Hz instead of 60 Hz.  So, your clock will gain one second per minute.

Spork

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Re: Gifted Generator / House AC Tolerance
« Reply #2 on: October 15, 2015, 08:52:45 PM »
The 61 Hz can probably be tuned down.  That's just a governor tweak.  I read somewhere online to set it between 62 and 62.5 at idle for it to be 60 with load.  I suspect that means different loads will be slightly different frequencies.

The governor adjustment is super sensitive.  The tiniest adjustment will add 2 Hz.... so it takes a while to chase it to the exact spot -- then tightening the lock nut will invariably throw it off by .5 or so.

Motors are pretty important here...  I want to run refrigerator/freezer... and possibly ceiling fans.
« Last Edit: October 15, 2015, 08:54:28 PM by Spork »

a1smith

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Re: Gifted Generator / House AC Tolerance
« Reply #3 on: October 16, 2015, 04:59:24 PM »
From what I read 120V appliances are made to run at 110V with no problem to account for voltage drop in extension cords, house wiring, etc.  So, you are just a few volts lower.  The refrigerator/freezer and ceiling fans are going to have induction motors so the frequency isn't a problem.  You can run them with regular AC, check motor temps and then run them on generator and check motor temps again.  Unless there is a big difference you should be fine.

paddedhat

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Re: Gifted Generator / House AC Tolerance
« Reply #4 on: October 16, 2015, 06:19:44 PM »
Running, and running under load are two entirely different values. I would find a high amperage tool, like a circular saw, and/or a space heater and run both of them, (depending on how big the unit is), while watching the voltage. It sounds to me that you are listing the unloaded values at idle, and you may be quite disappointed when you see how low the voltage drops when it's running hard, and trying to push anywhere near the name plate amperage. As for an acceptable low number? I have a fairly sophisticated electronic voltage guard system on my RV. It will open the incoming feed if the voltage drops below 102Volts for more than a few seconds.

Spork

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Re: Gifted Generator / House AC Tolerance
« Reply #5 on: October 16, 2015, 06:56:18 PM »
I did try running a compressor.  The meter drops out totally for about a second.... and then kicks back in at (can't really remember) about 104v.  But it is GONE for a split second.

Not knowing, my question is: Is that going to kill my fridge, freezer, LED lights, water heater*?\

This thing was free, so if tinkering with it and putting minimal parts into it was a total loss, I'm okay with it.  But if it will get me through a few probable days of no power every year or so... all the better.


*water heater is a tankless gas heater... so we're it's just providing a spark and opening/closing solenoids for gas flow.   But it definitely has some circuit boards in it, so I'm worried about low voltage/dropouts.

paddedhat

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Re: Gifted Generator / House AC Tolerance
« Reply #6 on: October 16, 2015, 09:09:03 PM »
104V is heading real close to about as low as I would push it. That said, what is the nameplate rating on the genny?  3500watts, 5500watts, or ? What is the running amp draw on the compressor? The temporary loss you saw on the meter was something know as Full Load Amperage, sometimes appearing as "FLA" on a motor nameplate. This is the temporary, and exponentially higher amperage load of getting the motor from a dead stop to full speed. It is totally normal. My guess is that running the genny anywhere close to full capacity, say 80% or so, is going to get you well below the 102 threshold, and into potential damage to any connected loads. From my experience, when it comes to low supplied voltage, the very first thing to take the hit is electronics, and in the case of RVs, it's typically the control board that run the appliances.

Spork

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Re: Gifted Generator / House AC Tolerance
« Reply #7 on: October 17, 2015, 07:25:22 AM »
It is listed as 4kw with a 6.6kw surge.

Generac 4000 EXL.  (Yes, I know Generacs are much hated among many of the trades.)

Compressor is listed as 15amp, though the motor plate isn't visible without taking off a bit of plastic housing (or my morning eyes can't find it pre-coffee).


...and you've hit the nail on the head.  It is precisely the internal computers in appliances I am worried about.  And now that most of our lighting has been changed over to LED, even our lighting is nothing but sensitive electronic devices. 

It was free... and if it's at the edge of what is usable, I am pretty sure I can sell it on craigslist.  I've got about $100 in it, the majority of that being a fresh battery for the starter.  If nothing else, it was an entertaining project getting it running.

paddedhat

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Re: Gifted Generator / House AC Tolerance
« Reply #8 on: October 17, 2015, 08:10:19 AM »
Spork, before you give up, plug the compressor and a hair dryer in and run them both. This should give you at least a 3200W load. Then take a voltage reading.

Spork

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Re: Gifted Generator / House AC Tolerance
« Reply #9 on: October 17, 2015, 10:34:37 AM »
Here's the latest results.  This was done with my compressor and a 1500 watt space heater.

Before I started, I measured both on city power:

compressor: 9amp, 700watt
heater: 12amp, 1500watt

I started generator and allowed it to warm up.

Unloaded, I measured both 120v circuits:
#1: 120v, 62.2hz
#2: 120v, 62.2hz

Loaded:
#1 (compressor): 114v, 60hz
#2 (heater): 108v, 60hz

swapped the loads, just to try to be complete:
#1 (heater): 112v, 60hz
#2 (compressor): 115v, 60hz

So (in my very nonexpert opinion) this seems pretty reasonable to me. 

Any idea what changed here?  The only thing I have done to the generator since the original post was adjust the valves.  Is that what has changed things?  Or was putting a higher load what changed it?  Or is the voltage regulator allowing this thing to just wonder around?

paddedhat

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Re: Gifted Generator / House AC Tolerance
« Reply #10 on: October 17, 2015, 10:46:31 AM »
Wish I had an answer for you. I can say that IMHE, most (non- top shelf Japanese brand) smaller, construction grade generators tend to be fickle bastards. I have seen one that work fine for nearly all tasks, but refuses to run an electric pump that's far below it's amperage rating. Other's that will surge and run rough one day, and smooth the next. I've had a bunch over the years, but the only one I will never let go is my little Honda 2000 "suitcase" genny.  By far the best tool I ever bought. Reliable as a anvil, sips fuel, and stunningly quiet.

Spork

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Re: Gifted Generator / House AC Tolerance
« Reply #11 on: October 17, 2015, 12:29:40 PM »
Wish I had an answer for you. I can say that IMHE, most (non- top shelf Japanese brand) smaller, construction grade generators tend to be fickle bastards. I have seen one that work fine for nearly all tasks, but refuses to run an electric pump that's far below it's amperage rating. Other's that will surge and run rough one day, and smooth the next. I've had a bunch over the years, but the only one I will never let go is my little Honda 2000 "suitcase" genny.  By far the best tool I ever bought. Reliable as a anvil, sips fuel, and stunningly quiet.

You are absolutely not the first person I've heard say that.   And long term: I want a bigger generator.   But free is hard for my little cheap ass bastard heart to resist.

My actual wish list:
* diesel - because it stores well and I have a 55 gal drum (usually not filled to capacity) of red diesel sitting around anyway.
* large enough to run a small welder
* small enough as to be portable.  ("Portable" includes anything I can pick up with a front end loader, so that really just means "not bolted down".)


On a slightly different side thread:
Original owner lost the 12v charger.  Is there any reason I can't just repurpose a cheap 12v power supply from my big pile of sad computer parts?  I.e., does a gelcel need some sort of smart battery charger that will cut out when it is fully charged?  Or can I just hang a 12v charger on it full time without damaging the battery?

paddedhat

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Re: Gifted Generator / House AC Tolerance
« Reply #12 on: October 17, 2015, 12:39:07 PM »
Yea, unfortunately, you need a smart trickle charger to keep the battery happy.

Syonyk

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Re: Gifted Generator / House AC Tolerance
« Reply #13 on: October 18, 2015, 01:21:45 PM »
Well, given that your computer power supply will put out ~12v, plus or minus a bit, and 12.0v is nearly dead for a lead acid battery, that's not going to work.  You want something that will float charge the battery, so somewhere in the 13.5-14v range, typically.  Just buy a little lead acid battery tender.  They're cheap on eBay.

Spork

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Re: Gifted Generator / House AC Tolerance
« Reply #14 on: October 18, 2015, 01:22:29 PM »
update:  I dug into it and found an adjustment pot on the voltage regulator.  I bumped the voltage up a tiny bit and now I'm getting between 110v and 115v loaded.  The 2 legs still have a 5 volt difference, but they're at least a minimum of 110v.  I really only want to run a small number of 120v circuits (no 240v circuits) ... so it doesn't seem to me that the 5v difference in the 2 legs should matter.

Spork

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Re: Gifted Generator / House AC Tolerance
« Reply #15 on: October 18, 2015, 01:24:19 PM »
Well, given that your computer power supply will put out ~12v, plus or minus a bit, and 12.0v is nearly dead for a lead acid battery, that's not going to work.  You want something that will float charge the battery, so somewhere in the 13.5-14v range, typically.  Just buy a little lead acid battery tender.  They're cheap on eBay.

I've got a 12v auto trickle charger.  I'm assuming that will work? 

Syonyk

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Re: Gifted Generator / House AC Tolerance
« Reply #16 on: October 18, 2015, 03:18:45 PM »
Yeah, an auto 12v charger is fine.  That's designed for a "12v" lead acid battery, not "computer +12v," which is *actually* 12v.

It gets worse when you get into electric bike battery packs.  A "24" or "36" volt pack is almost guaranteed to do nothing of the sort, since there are a few different voltages that all qualify to be called that, they vary based on chemistry, and lithium batteries have a fairly wide working range (a pack that's fully charged at 42v will be fully empty around 32v).

zolotiyeruki

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Re: Gifted Generator / House AC Tolerance
« Reply #17 on: October 19, 2015, 01:42:03 PM »
update:  I dug into it and found an adjustment pot on the voltage regulator.  I bumped the voltage up a tiny bit and now I'm getting between 110v and 115v loaded.  The 2 legs still have a 5 volt difference, but they're at least a minimum of 110v.  I really only want to run a small number of 120v circuits (no 240v circuits) ... so it doesn't seem to me that the 5v difference in the 2 legs should matter.
Nice! I wouldn't worry too much about the small difference in the two circuits.  It sounds like you got yourself a nice working generator (and the knowledge to repair it!) for $100.

Personally, I'd be more concerned about the kind of waveform coming out of the generator than it's exact frequency or voltage.  Spikey waveforms are bad for electronics.

Spork

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Re: Gifted Generator / House AC Tolerance
« Reply #18 on: October 20, 2015, 12:01:12 PM »
I have no oscilloscope to try to examine the wave form.

My "traditional" electronics (computers, tivo, etc) hang off of a UPS, which (in theory) should smooth out some of the dirty power.  The only things I worry about are the silly internal electronics in the fridge/freezer/LED lights.

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Re: Gifted Generator / House AC Tolerance
« Reply #19 on: October 20, 2015, 02:03:30 PM »
I have no oscilloscope to try to examine the wave form.

My "traditional" electronics (computers, tivo, etc) hang off of a UPS, which (in theory) should smooth out some of the dirty power.  The only things I worry about are the silly internal electronics in the fridge/freezer/LED lights.
I think it's a mistake to assume that your UPS also includes a power conditioner. Most UPSes are pretty simple--they have a battery charger, some batteries, a modified square wave inverter, and a relay to switch the outlets from straight mains power to inverted power.  The output waveform on those is pretty scary--it's nothing like a sine wave at all.

Now, you *might* have an online UPS, which feeds its outlets from the inverter 100% of the time, and you *might* have an inverter that outputs something closer to a sine wave, but I doubt it.

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Re: Gifted Generator / House AC Tolerance
« Reply #20 on: October 20, 2015, 03:11:39 PM »
Re sine wave inverters: If you don't know if you have one, you don't.

Spork

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Re: Gifted Generator / House AC Tolerance
« Reply #21 on: October 20, 2015, 03:22:48 PM »
Re sine wave inverters: If you don't know if you have one, you don't.

It's from the APC Smart UPS line.  My limited understanding is that they are true sine wave inverters.  I can't say I've ever looked at the output on an O-scope.