Generators And Inverters

[Paul]

I have a vintage Honda generator which outputs 12 or 24v, no AC output. 

I have a couple of power inverters which turn 12v dc into 230v ac

I need to understand the compatibility and capability of both as in is the output of the generator great enough to power the inverters and to what load? Is the critical load on the generator dependent on the size of the load on the inverter or is it the maximum load of the inverter regardless of what is plugged into it?

What I want to do is use the gennie to drive the larger inverter (1500w) then use that to power garden machinery rated at 600 - 800w. What I need to work out is what load an 800w machine plugged into a 1500w inverter places on a 12v generator? Is there some magic formula to work it our?

[NorfolkNog]

Bit over my head Paul (Nigel might be the man) but fag packet calculation, I think the inverter could potentially draw 120 amps from the 12 volts output at full power. Do you know what the power output of the generator is? 

[Regulo]

Power in = power out. So 800W at 240V is approximately 3.33 amps. 800W at 12 volts is approx 66.6 amps. Thus the rule of thumb is Amps at 12volts is 20 times the Amps at 240 volts. Does that help? 

[MauriceMynah]

If I remember correctly, Honda used to make small gennies for recharging batteries. To wire one to an inverter whilst possible, would probably give enough umph to light a small LED light. Try to draw more and listen out for the small "pop" and smell of burning. 

[Islander]

Hi Paul. To keep things really simple. Devide Watts by 10 to get approx amps required by inverter.

i.e.  800w =  80A

This will allow for the efficiency of the inverter. They are never as good as they tell you.

The inverter will only draw a few hundred milliamperes without a load.

As MM has said the gennie won't like this set up but put a good size battery in and it should cope with the switch on surges your tools will require.

Hope this is of some help.

Colin 

[annv]

Hi Paul As Colin said if you use a battery as a reservoir it will work, if not it will stall the generator and damage it if used directly as a power source, buy a longer 2'5 arctic cable and run from mains, lot cheaper and no noise providing you have main's of coarse,good idea but NO!!. John

[Paul]

Thanks everyone. You have reaffirmed what I expected. Treating the inverter as "transparent" and converting the amps at 230v to amps at 12v puts me in the 80a bracket which is beyond the means of my little genny.

I want to be able to power electric garden tools, hedge trimmer, pole saw and tiller which rate between 550w and 1000w to help maintain the local community garden. Sadly we have no mains connections, power or water. We used to be able to get them from the adjacent community center but sadly that facility has been withdrawn due to a dispute with the parish Council over access to the garden. We are in the process of raising money to have mains water bought into the garden but as the dispute with the PC has also led to removal of funding it is a tough ask, these things are not cheap. 

The local school are helping out with water but it is too far to run power cables, not to say unsafe for the children so we need to come up with an answer. I think it will have to be a stronger generator with a 230v outlet. This leads to another conundrum as they are rated in KVa which seems to bear no resemblance to watts. I thought I'd found a decent second hand one yesterday, rated at 2.2KVa which I thought should be plenty but  checking further it was only 1000w.

So next question, in order to run a 1000w constant load, what KVa rating should I be looking for?

[grendel]

it really depends what that load is, as if it has a motor the starting current will be higher, generally the kVA is equivalent to kW, but its quoted that way as power factor correction comes into play, depending upon the load it can shift the phase off angle, changing the effective kW, but if you quote in kVA then this allows for that adjustment. (thats also where the starting current comes into play, you may need a 2000W generator to accomplish a startup - this may be why the genorator is rated at 2.2kVA as it may handle motor startup, but its worth asking the question before buying

[Paul]

Thanks Grendel. In such things I tend to work on the theory if I need 1kw have the capacity for 2, I find these things are best not operated at their full capacity for long periods. I did try and find a calculator on the web and the result gave me scientific formulae the likes of which I have not seen since my A level maths, which I failed!

There seems to be quite a watershed in price between 2.2kva and 3kva plus generators, the former being available for a couple of hundred quid upwards but the latter costing four figures plus.

[annv]

Hi Paul Suitcase genys tend to be 2.2 kva = 2200w= 8/9 amps max and air cooled anything, bigger/higher output needs a trolly not very lightweight, building site ones 110 volt ie in a frame/air cooled and noisier but lighter, but still need two people to lift/carry,   5/6 kva tends to be starting output for on board power, bolted in and water cooled or trolly mounted with radiator. You will be better off getting petrol powered strimmers/ grass cutters you then will be completely mobile ie councils  ground workers don't use electric only petrol powered ones they are safer to no cables to cut/trip over and lighter to carry/use. John

[Paul]

On 19/01/2020 at 18:34, annv said:

You will be better off getting petrol powered strimmers/ grass cutters you then will be completely mobile ie councils  ground workers don't use electric only petrol powered ones they are safer to no cables to cut/trip over and lighter to carry/use.

Agreed, though I disagree that petrol powered are lighter, but it would cost in excess of three thousand pounds to replace our existing equipment with even modest petrol stuff and right now that is not an option. We are already looking at a bill of 11k to install water to the site and without funding from the Parish Council the Community Garden's income is in the region of 500 a year. 

So we are already full steam ahead on cake stalls, table top sales etc, anything we can do to raise funds. We are appealing for help from the village in the hopes that somebody might have a suitable generator we can borrow. If not then it might fall to the organising committee to fund a second hand machine out of our own pockets.

[annv]

I have a diesel 6Kva 240 volt electric start generator with low hours you can have for £400=00 it will need a radiator as it came out of a boat. John

[RumPunch]

How many times a year do you do the work - could you hire a gene ?

[Bytheriver]

On 19/01/2020 at 13:56, Paul said:

Thanks everyone. You have reaffirmed what I expected. Treating the inverter as "transparent" and converting the amps at 230v to amps at 12v puts me in the 80a bracket which is beyond the means of my little genny.

I want to be able to power electric garden tools, hedge trimmer, pole saw and tiller which rate between 550w and 1000w to help maintain the local community garden. Sadly we have no mains connections, power or water. We used to be able to get them from the adjacent community center but sadly that facility has been withdrawn due to a dispute with the parish Council over access to the garden. We are in the process of raising money to have mains water bought into the garden but as the dispute with the PC has also led to removal of funding it is a tough ask, these things are not cheap. 

The local school are helping out with water but it is too far to run power cables, not to say unsafe for the children so we need to come up with an answer. I think it will have to be a stronger generator with a 230v outlet. This leads to another conundrum as they are rated in KVa which seems to bear no resemblance to watts. I thought I'd found a decent second hand one yesterday, rated at 2.2KVa which I thought should be plenty but  checking further it was only 1000w.

So next question, in order to run a 1000w constant load, what KVa rating should I be looking for?

Sthil now do an excellent range of battery kit which are fine for part day jobs and may save the hassle of genny & cables https://www.stihl.co.uk/STIHL-Products/080087/STIHL-Cordless-Power-Systems.aspx Been around for 3-4 years now so well tried & tested - I have used the blower & it runs for over 2 hours without loosing power

[annv]

Hi Paul Userly 50% ie 1500w=6amps it's not the constant running but the start up surg , lots of generators say they are one amount of power BUT in the small print they say this is only the start up figure the constant power output is often lower and the smaller one cylinder ones don't maintain the constant voltage hence the big price difference of small generators to bigger start point of 5/6 Kva generators that can maintain the correct voltage under load this isn't so important on small electric motors, if possible i would go for at lest a 2Kva ie 2000w suitcase/building site generator, try hiring one first to confirm that you get larger enough one to run your equipment. John

[Paul]

I think we have come to a decision. 

Originally we were concerned about the high startup current and low power efficiency of some of, if not most of our tools as they use induction motors which I am led to believe have the biggest gap between KW used and KVA needed to power them, a value I have learned is kVArs. I already have an evolution power tech engine on my pressure washer, which if you haven't come across them before is an engine on a trolley with bolt on accessories, on of which is a gen set. It runs at 2.8kw peak and 2.4kw continuous, which we now feel should be plenty for what we need. At 130 quid or so it solves our problems and I might be able to make use of it too. 

I also have a meeting with the chairman of the Parish Council tomorrow to try and put an end to the enmity between them and the community garden. Wish me luck with that, I'm the last person I'd send on such a mission.

[annv]

Hi Paul suggest you move meeting to local pub usually works well for both parties, best of luck, jaw jaw is better than war war. John

[Paul]

Thanks John. I did try! Almost all village clubs meet at the Cricket Club which has an excellent social club open every evening but alas it seems the impasse is absolute, for the moment at least. Sadly there is one member who was elected to the Parish Council at the last elections who is adamant that the community garden gets no support or funding from them unless we leave it open at all times "for the whole community to enjoy". We did try this over three weekends last year and had several plots vandalised, a number of fruit trees destroyed, the central arbor and seating area smashed, the poly tunnel slashed and obscene graffiti painted over the shed and many of the benches. Hence it now remains locked and will continue to be.  

At least we have now been able to demonstrate to the PC that we are not beholden to them in order to operate, and as I stressed to the chairman, Parish Councillors do come and go, especially unpopular ones. 

[Paul]

posting about the village in another thread reminded me of this one, and I thought it would be a good time to update it. I haven't been able to say a lot as it looked for a long time that this whole matter was heading to the courts, but common sense has prevailed. It has been a difficult time trying to get interested parties speaking in light of the pandemic, it seems those who want to talk know how to use zoom, or teams or some such things, those that don't have no idea, despite a son who used to run the local computer shop. 

It came to light that the person behind the vendetta against the community garden had an ulterior motive. Surprised? Neither am I. Although the garden currently has no road access, it does back on to the old parish room (from where we used to get water), a meeting room owned by the parish council now largely unused, the demolition of which would grant that valuable road access, and allow the community garden to converted to a car park. This satisfies the obligation to provide a free car park for the village which was placed on the charity when it obtained grants to buy the dance hall, which had a car park opposite which currently fulfills that obligation. With that removed, the land currently occupied by the car park could be sold for building land which would raise funds for the community charity to acquire the freehold of a piece of land currently occupied by a residential mobile home site which has been offered for sale for some time. There are those in the village who dislike the site, though it causes no problems, the people who live there are very respectable, many retired couples. It is not one of "those" residential mobile home sites, if you understand my meaning. 

As if this doesn't start to smell bad enough, the developer lined up to build the houses on the existing car park is non other than the brother of the lady at the middle of all of this. After more than thirty letters of complaint were sent to the chairman of the parish council about the self interest of the councilor in question she has decided to step down from the parish council, and from her position with the village community organisation. 

I understand that the plan fell apart when a specialist solicitor engaged by the community organisation advised them that use as a car park was unlikely to fulfill the terms of the bequest of the land used for the community garden. So it's as you were, except that we got our water pipe installed, thanks to a few generous benefactors not least the contractor who did all of the groundwork for a bottle of vintage scotch and a free advertising board at the village cricket ground. 

Oh yes, there is now a very nice house, rather large on the edge of the village for sale. "She" has decided to move on to pastures new. It's beyond my means sadly, and it is a shame as her other half is a thoroughly decent chap, spent many an evening propping the bar of the cricket club up "chewing the cud" with him.