Inverter questions.

[Benthosboy]

Howdo all.

The telly is sorted and the in-fill for the rear chassis is getting there, so next on the list:

As winter is drawing near, I'm toying with the idea of getting either a microwave or a mini oven for the cab. I'm away in the wagon for a minimum of 4 nights a week, sometimes 5 and occasionally 2 weeks, so a hot meal makes a nice change. I've looked at 24 volt ovens but I'm not overly impressed so low wattage mains gear seems to be the favourite.

Assuming a max draw of about 2 kW, can anyone recommend a decent inverter? I haven't got a fortune to spend, but I'd rather keep clear of "cheap and nasty" tackle. Are such things best wired direct from the battery with hefty cables, and fused?

As an aside, I'm just fitting a couple of 240 volt household sockets in the cab, wired for 24 volt use for the telly/booster, kettle, toaster, etc. I can't do with lighter sockets, the plugs always worry me and I've had a couple melt in the past, so I'm wiring the mains sockets using the earth and live pins and the same on the 3 pin plugs. It might sound like overkill but it makes sense to me.

Thanks in advance.

Martyn.

 

[Pete.]

A 2kw inverter is going to pull 83 amps at 24V, and that's not taking losses into account. I've got a 12v 600W inverter and that's got large leads on it, can't imagine what a 2kw one would use.

But are you saying that you're wiring 240V plugs for 24V power and using the earth as live and the other two as return? Can't see that hurting at 24V but god help anyone who accidentally plugs one of your appliances into the mains.

 

[rtbcomp]

You'd be better off with something like this for your DC power http://www.vehicle-wiring-products.eu/product.php/770/din-plug

Or https://www.roadpro.co.uk/retail/product_list.aspx?prod=Procar 12V and 24V plugs

I would wire the inverter straight to the battery with + & - leads, I wouldn't rely on the body for earth return. Also fit a fuse as close as possible to the battery.

 

[RonA]

Howdo all.

The telly is sorted and the in-fill for the rear chassis is getting there, so next on the list:

As winter is drawing near, I'm toying with the idea of getting either a microwave or a mini oven for the cab. I'm away in the wagon for a minimum of 4 nights a week, sometimes 5 and occasionally 2 weeks, so a hot meal makes a nice change. I've looked at 24 volt ovens but I'm not overly impressed so low wattage mains gear seems to be the favourite.

Assuming a max draw of about 2 kW, can anyone recommend a decent inverter? I haven't got a fortune to spend, but I'd rather keep clear of "cheap and nasty" tackle. Are such things best wired direct from the battery with hefty cables, and fused?

As an aside, I'm just fitting a couple of 240 volt household sockets in the cab, wired for 24 volt use for the telly/booster, kettle, toaster, etc. I can't do with lighter sockets, the plugs always worry me and I've had a couple melt in the past, so I'm wiring the mains sockets using the earth and live pins and the same on the 3 pin plugs. It might sound like overkill but it makes sense to me.

Thanks in advance.

Martyn.

This may not be directly relevant to what you're trying to achieve but is my experience with an inverter in a caravan. It came about as a result of arriving on some campsites & finding all the plots fitted with electric hookup having gone.
To try & make myself self sufficient, I invested in a solar cell (175 W) to independently charge up the leisure battery & a 1400 W DC to 240 V inverter to power the appliances (including a fitted microwave) in the caravan.
The solar side of the arrangement worked brilliantly & will fully charge the battery even on relatively overcast days. However the inverter didn't live upto expectations. The unit would power a TV or similar for an evening, the problems arose when trying to use the microwave. Although the microwave used less than 1000W it would very quickly drop the DC battery voltage from fully charged (12.8V) to the point where the inverter would automatically shut down (12V) to protect the leisure battery.
Using the larger 24V found on a lorry might have made the operation more viable, but by the same token doubtless you wouldn't want to drop your vehicles battery voltage to a point where it wouldn't operate the starter motor.
I did consider fitting a second battery to increase capacity but as this would necessitate fitting a second battery box as well I haven't as yet persued that avenue.

RonA

 

[wookie]

the problems arose when trying to use the microwave. Although the microwave used less than 1000W it would very quickly drop the DC battery voltage from fully charged (12.8V) to the point where the inverter would automatically shut down (12V) to protect the leisure battery.

If you want it for the microwave you could keep your engine running for the 5 mins that the microwave is on just to keep the voltage up. Also check out how efficient the inverter is at say 10-20% capacity, some can be as bad as 50% at low power. With that in mind you might be better with 2 inverters, one high power for the microwave and a 200-300 watt one for everything else e.g. your tv/laptop etc

 

[500e]

http://www.trucknetuk.com/phpBB/viewtopic.php?f=2&t=84688
A lot of discussion

http://www.roadking.co.uk/mobile-12v-and-24v-microwave-ovens.html

http://www.whispaire.co.uk/microwave1.html

 

[normspanners]

I have a 12v 240v 2kw inverter and it runs my small jet wash for washing rally cars. That draws 6A but no wattage on it but at those amps must be 1500W, It flows roughly the same as my 2.5 hp petrol one so i would guess that is about correct. I use it hard wired and a paralleled spare truck battery, plus leaving the engine running fast idle it copes fine, I have tried and run a micro wave off, it I am sure but I cannot remember which one I tried, at the minute the car with it in is 60mls away so cant test it for you.
A 24v one should cope very well as the input amps will be halved, or even less because truck systems go to nearly 30v running.

 

[Benthosboy]

Thanks for all the replies, chaps. I might have a rethink and see about a 24 volt oven. Fitting an inverter for a microwave seems a bit of a performance, and tbh, I enjoy cooking my tea rather than ready meals so I don't know if it would be worth it.

Pete: don't worry about anybody plugging my 24 volt kit into the mains. There's only me drives "my" wagon and I'm away all week anyway. When I'm on my hols, it's usually parked-up in the yard, and the lads are a good bunch and tend to respect other folk's gear.

Just out of interest, what would happen if a 240 volt appliance was plugged into my 24 volt-wired mains socket? Presumably it simply wouldn't work?

And thank you 500e, some food for thought in your post. (No pun intended)

 

[normspanners]

As I am typing this I have one of my kitchen M/waves 1300W running off my leisure battery and my 800W inverter 1200W surge , set for 5mins heating a cup of water the voltage went from fully charged to 12.47 V and now is with 30 sec to go at 12.2v it has just finished, water is not quite boiling and the battery has recovered back to 12.7v
PS m/wave sounded fine .
So there you are it works off an 800w one, I will now test my 600W one, It is a higher spec /better quality inverter, ie gives a better type of sine wave. Now that one started ran for 30 secs and the inverter shut down it has a higher surge 1800W than the other but doesnt like the continuous current.
So a 2kw should cope fine at 24v needs hard wiring though.

 

[normspanners]

Have i done all that for nothing
agh well at least I learnt sumat!!

Just out of interest, what would happen if a 240 volt appliance was plugged into my 24 volt-wired mains socket? Presumably it simply wouldn't work?

Dont think it will do them any good with 24v high current up the earth lead especially any thing with a transformer in the power supply that will get mighty warm very quickly!!!

 

[rtbcomp]

As an aside, I'm just fitting a couple of 240 volt household sockets in the cab, wired for 24 volt use for the telly/booster, kettle, toaster, etc. ....... I'm wiring the mains sockets using the earth and live pins and the same on the 3 pin plugs. It might sound like overkill but it makes sense to me.....

.............
Just out of interest, what would happen if a 240 volt appliance was plugged into my 24 volt-wired mains socket? Presumably it simply wouldn't work?

Dont think it will do them any good with 24v high current up the earth lead especially any thing with a transformer in the power supply that will get mighty warm very quickly!!!

It certainly wouldn't work.

Using the live & earth pins for your 24v DC and the 240v appliance was double insulated nothing would happen because the earth connection in the socket would be unconnected.
Nothing should happen on an earthed appliance because there shouldn't be a path between live and earth in the appliance.

 

[normspanners]

I'm wiring the mains sockets using the earth and live pins and the same on the 3 pin plugs. It might sound like overkill but it makes sense to me.

I read it as combining the live and earth because of the "overkill" comment because a 13amp fuse would blow easily on 24v at 300w ish. Because the cigar lighter plugs are usually 16amp and the ovens and toasters are usually 300/400/500w micro waves 750/800W the 13amp fuse will struggle.

 

[ajlelectronics]

Two things:

1) How about an inverter generator? They are small and quiet, Machine Mart do them for under £300 I believe.

2) Low voltage connectors would be better as Hella (Powerlet) type. They can handle 10A continuous and can't be interchanged with anything else.

 

[rtbcomp]

I read it as combining the live and earth because of the "overkill" comment because a 13amp fuse would blow easily on 24v . Because the cigar lighter plugs are usually 16amp and the ovens and toasters are usually 400/500w the 13amp fuse will struggle.

If he did that in the plug he'd short out the fuse.

He still wouldn't gain extra current capacity because the neutral has to carry all the current.

As mentioned by ajlelectronics in #13 and myself in #3 the best solution would be to use connectors designed for the job.

EDIT - remove confusion!

 

[normspanners]

2) Low voltage connectors would be better as Hella (Powerlet) type. They can handle 10A continuous and can't be interchanged with anything else.

most low voltage cooking equipment is, as said, starting at 300w and upwards therefore at 12v= 25A and 24v =13A many truckers use small anderson type plugs on their high current stuff.

If he did that in the plug he'd short out the fuse

If combined it would not short the fuse it would share the load through the earth pin and the fuse , exactly my point then the fuse would not blow.

 

[ajlelectronics]

Agreed Norm, however, I was suggesting doing away with the inverter and using a generator. then all the low voltage stuff would be realistic at a limit of 10A per appliance. An inverter providing 2kW is not something to use from leisure batteries in my opinion, there is so little time available and the high currents involved would concern me.

 

[rtbcomp]

If combined it would not short the fuse it would share the load through the earth pin and the fuse , exactly my point then the fuse would not blow.

If you remove the fuse and plug the plug into the socket you'll get continuity between the ends of the fuseholder, that to me is a shorted fuse. Although I take your point about load sharing, the point I made in #14 about the neutral conductor still applies. Rather than go to the hassle of doubling up the wiring to save the fuse you might as well wire a dead short across the fuse holder and provide circuit protection elsewhere (which you'd have to do anyway).

At the end of the day all this is academic as the OP states quite clearly he intends using the live and earth pins, I don't see how you interpret that as connecting live & earth together, I'm sure by "overkill" he's referring to the connector size.

If he insists on using mains plugs & sockets he'd be better off using the old unfused 15A type, still available from CPC &c.

 

[Pete.]

I assumed he meant to use the earth pin as one conductor and the live and neutral wired parallel as the other. Can't think of any other way it would work to reduce the odds of melting the plug.

 

[rtbcomp]

I assumed he meant to use the earth pin as one conductor and the live and neutral wired parallel as the other. Can't think of any other way it would work to reduce the odds of melting the plug.

I wondered about that, but he just mentioned live and earth. I guessed he was trying to avoid problems if 24v appliances were to be plugged into the mains or vice-versa by using live & earth.

 

[normspanners]

I do work for a guy, coffee Col we call him, who runs a mobile, posh coffee shop around offices and garages etc, he runs a Full- on 240 v coffee machine and was using a suzuki jimmy,van, tiny engine / alternator and start battery, with a 3kw inverter and 12v medium sized fridge, for 8hrs a day 5days a week he just used a large leisure battery paralleled to his start battery and charged it at night. And he even used to shut off the engine at calls for ten mins or so !!. Has since changed to a merc van with large cooler for sanwiches and microwave.
The only thing he said he changed the leisure at least every 12mths because as they aged they wouldnt do a full day!!, in fact the one I was running the microwave off last night was one of his discarded batteries still works as a jumper or a power source for me.


Not him but you get the idea the fridge in this is on the passenger side.