Portable Generators - follow up question

Submitted: Saturday, Jan 22, 2011 at 11:18

ThreadID: 83818 Views:3524 Replies:2 FollowUps:6

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KenInPerth

I have been reading the thread 18th Jan about Portable Generators and the "discussion storm" it generated. It seemed to get well off track for the question asked albeit the points stressed about legalities and dangers were valid and should be taken note of. But let's face it - most people are just going to do what they need to do to get power in the RV / Camper.

Can I ask some questions of those that are obviously experienced elctricians in that discussion that may help the original question which is nothing to do with wiring, modifying, or doing anything dangerous.

This in a nutshell is what I have been told about generators:

1. the honda's EUi models are inverter type generators in that they electronicly generate good clean "pure sine wave" output that is well regulated and "friendly" to the more sensitive electrical and electronic appliances, and can adjust themselves according to load so they can run quieter on low loads.

2. standard armature type generators do not produce clean "sine wave" output but are similar to poorer quaility inverters that produce an output that "approximates a sine wave" and are not well regulated in that the voltage can fluctuate with the motor and are not so "friendly" to sensitive equipment.

So questions:

1. if you were concerned about looking after your sensitive devices (camera's, laptops, TV, etc) as well as running your air con and microwave you would purchase an EUi albeit at a higher cost - bearing in mind also it must be large enough to cope with the high current devices (2.4 or better as per discussions) and you will generally have a quieter running unit?

2. if you only wanted something to really run the high current devices like Microwave and Air Con would you be OK to go with the cheaper gen set or is there proven examples of damage to equipment using these gen sets?

3. is there a difference between cheap and more expensive gen sets (non electronic) in so far as the quality of the output power - comparing something like a Honda and a cheap import?

I know there will be a lot of "we have used a cheap generator for years and had no problems" type comments, and that will probably be the majority case.

Ken

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Reply By: Notso - Saturday, Jan 22, 2011 at 11:41

Saturday, Jan 22, 2011 at 11:41

"standard armature type generators do not produce clean "sine wave"

Actually Armature Style generators do produce a clean sine wave, the cheap ones just have problem with poor voltage and frequency control.

AnswerID: 442675

Follow Up By: KenInPerth - Saturday, Jan 22, 2011 at 11:49

Saturday, Jan 22, 2011 at 11:49

that was my understanding from my "school days" but I was told by a "Honda Shop guy" that was not the case - hence my question.

Ken

FollowupID: 714683

Follow Up By: Notso - Saturday, Jan 22, 2011 at 12:37

Saturday, Jan 22, 2011 at 12:37

The concept of Modified Sine wave only arrived when cheap inverters were developed that produced a square wave or stepped wave to simulate a sine wave.

More expensive inverters produce the pure sine wave that has always been the characteristic of an armature style Alternator.

FollowupID: 714694

Follow Up By: dbish - Saturday, Jan 22, 2011 at 15:35

Saturday, Jan 22, 2011 at 15:35

I recently repaird the AVR unit on a cheep Bunnings GMC 1000W 4stroke generator. After repair the voltage only varied 5v betwean full load800w & no load & the sine wave was as clean as my local mains. In fact the local mains can vary from 220v to 250v here.

FollowupID: 714710

Follow Up By: oldtrack123 - Sunday, Jan 23, 2011 at 00:06

Sunday, Jan 23, 2011 at 00:06

Hi Ken
I will not go into the pros & cons of different as my only experience is with Honda
What I will do is give you an outline of the two Types:

Using your term armature type
[not technically correct but we both understand what you mean]
[1]These generally, simply by design,produce a very good sine wave output
[2] the frequency is directly proportional to the speed Ie engine slows down ,frequency drops same % with no means of correcting
[3]Voltage is also speed dependent but can be adjusted within limits with an automatic voltage control [AVR]
[4]Ability to cope with sudden heavy load changes & maintain constant speed is very dependent on the engine power & governor response time.
The major problem with these types is ability to meet reqs of[4]

with inductive loads[motors, microwaves etc the ]frequency drops due to speed changes the current rises dramatically,further loading the engine possibly to the extent that the engine may stall
Basically the engine needs to powerful enough & the governor needs to respond quick enough for speed to remain relatively constant

With the inverter type :

[1]wave form depends heavily on design with pure sine wave being much more complex
[2]Frequency is not speed dependent as it can be controlled,within limits electronically.This again depend on design & quality
[3]voltage also can be controlled within limits,but just how good again depends on design & reliability
[4]ability to cope with sudden heavy load changes is much less a problem AS maintaining the frequency can allow the engine time to recover[again within
limits
This means that motors ,air cons,etc starting can be done with a smaller engine.
For heating ,lighting etc [resistive loads]there is not much to gain with an inverter type
however even the inverter type with eco throttle setting[such as Honda can /do have problems with sudden heavy load increases if running on eco setting

This probably has not helped you much but perhaps you understand the pros & cons

Peter

FollowupID: 714787

Follow Up By: KenInPerth - Sunday, Jan 23, 2011 at 11:06

Sunday, Jan 23, 2011 at 11:06

Thanks Peter (Oldtrack123)

That is a great help to me and has explained a lot more about why you probably should use one type over the other and pay the extra money.

Hopefully it may also help Colin M's original question.

So from what you are saying the biggest effect comes from frequency variation of the output - and I would assume we are talking larger motor units like air con's, fridges, big drills and saws, etc. rather than the battery charger, laptop, TV, etc that are much lower power.

I guess for most people then it comes down to a couple of things

1. if cost is not the object then buy the right sized "pure sine wave" Inverter model and you should have some comfort in the fact it will be kind to all your equipment and hopefully provide good service (bearing in mind more complex = potentially higher repair costs if something "breaks").

2. if cost is an object and you go with a "normal" generator you may risk either damage to (or reduced life of) some of your equipment. But having said that, there is probably thousands of people out there running on "low cost" generators and surviving (including building sites and their electric tools) - I guess it comes down to how tolerant any individual piece of equipment is to variations in frequency / voltage and for how long and how long the generator will put up with major "hits" in terms of large startup loads.

For me the only reason I would want a generator in any location would probably be for air con if required as I have to travel and work in some pretty hot locations. Otherwise I can and would would use Gas / Battery for equipment and the Car engine / Solar for re-charge.

Ken

FollowupID: 714812

Follow Up By: oldtrack123 - Monday, Jan 24, 2011 at 00:27

Monday, Jan 24, 2011 at 00:27

Hi Ken
Yes ,they are the conclusions I would expect.
Go to the top of the class
I am pleased to see you understand the applications& implications

But if further explanations are required just ask the question.

Peter

FollowupID: 714895