12v to 240v Power Inverter

Submitted: Tuesday, Aug 26, 2003 at 14:13
ThreadID: 6844 Views:3071 Replies:9 FollowUps:10
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Hi all,

Just wondering if any of you guys have a power inverter permanently installed in your trucks.

I have a 500w (800w peak) inverter that i want to be permantly wired in and would like to know what size/type of cable to use ?

Also what fused protection can be used as it will be run to the rear cargo area approx 3 meters ?

Any ideas ???

Kev.
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Reply By: Mick - Tuesday, Aug 26, 2003 at 14:46

Tuesday, Aug 26, 2003 at 14:46
Hi,
I wouldnt use anything under a 16 square mm cable for your 3m length.
You can use an "ac" circuit breaker rated to around 16 - 20 amps, as amps are all the same with ac or dc, I use this in my truck & works great.
Another alternative is using a fuseable link with a short piece of thin wire only between the 16sq. mm cable. Your local auto elec could give you some pointers on what wire to use.
AnswerID: 29201

Follow Up By: Kev - (Cairns,QLD) - Tuesday, Aug 26, 2003 at 15:10

Tuesday, Aug 26, 2003 at 15:10
16 mm2, thats big cable.

I like the circuit breaker idea but i need it to be water proof and havent room for an enclosure, maybe a plug in fusable link will work.

Thanks.
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FollowupID: 20330

Reply By: Member - Wherethehellawi - Tuesday, Aug 26, 2003 at 14:51

Tuesday, Aug 26, 2003 at 14:51
IMHO > As 240v can kill i would recommend using a circuit breaker in lieu of fusible link and an auto electrician is not an authority when it comes to 240v. Best to consult a qualified electrician for this.Wow! am I cute
If yer ain't fishing, Yer ain't livin
Richard
AnswerID: 29202

Follow Up By: Kev - (Cairns,QLD) - Tuesday, Aug 26, 2003 at 15:04

Tuesday, Aug 26, 2003 at 15:04
I think he means to use a AC breaker on the 12volt high current side to protect the cable, the inverter has its own 30 amp fuses.
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FollowupID: 20329

Follow Up By: Member - Wherethehellawi - Tuesday, Aug 26, 2003 at 19:11

Tuesday, Aug 26, 2003 at 19:11
No I do not mean to use a AC breaker on the 12v circuit. I refer to the 240 volt circuit

But if what you say, is that they ( the inverters) have 30 amp protection on 240 v side for what would be no more than say an general purpose outlet in a house (which is 16 amps protection these days (15 old)) is a bit over the top. A 15 amp house-hold power outlet ( which has larger earth pin) can have 20 amp protection.

Wow! am I cute
If yer ain't fishing, Yer ain't livin
Richard
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Follow Up By: Member - Wherethehellawi - Tuesday, Aug 26, 2003 at 19:17

Tuesday, Aug 26, 2003 at 19:17
isnt an 800 watt inverter only 3.3 amps (or thereabouts) at 240v...so why 30amp protection?Wow! am I cute
If yer ain't fishing, Yer ain't livin
Richard
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FollowupID: 20354

Follow Up By: Kev - (Cairns,QLD) - Tuesday, Aug 26, 2003 at 19:30

Tuesday, Aug 26, 2003 at 19:30
Now i think im getting confused !

There are two 30 amp fuses (maybe in parallel to = 60 amps) on the inverter wich i suspect would be for over current protection on the 12v DC side of the inverter.

I will need a fuse at the battery for cable short circuit protection.

As for the 240v AC side i find the inverter shuts down when over loaded so im not concerned about a 240v circuit breaker.

Im getting there !
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FollowupID: 20356

Reply By: Mick - Tuesday, Aug 26, 2003 at 15:24

Tuesday, Aug 26, 2003 at 15:24
16 mm2 isnt that big, get your aout elec to show you some.
Put the link or breaker close as you can to the battery, then if the wire rubs through past the battery you will be saved! My circuit breaker is up close to the battery on the inner guard and doesnt get wet.
AnswerID: 29212

Follow Up By: Kev - (Cairns,QLD) - Tuesday, Aug 26, 2003 at 15:41

Tuesday, Aug 26, 2003 at 15:41
I know how big 16mm2 is, thats the size of a incoming mains on a house. (i think)

What i forgot to mention is that i doubt i will load the inverter to the max anyway, just lighting ect so hopefully i can get away with 6-10mm2.
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FollowupID: 20334

Reply By: Dennis (Brisbane) - Tuesday, Aug 26, 2003 at 15:48

Tuesday, Aug 26, 2003 at 15:48
The quote ...... "as amps are all the same with ac or dc"

BULLSHI*T

And yes I am an electrician.

*A*lternating *C*urrent by its very nature alternates (or oscillates) back and forward 50 times a second (50 Hz), therefore it is 'easy' to break the arc between two current carrying contacts as they part (a switch or a circuit breaker). The arc will self extinguish because it is trying to go back and forth. Obviously this arc is harder to break the higher the voltage (the pushing force) and the higher the amps (the working energy).

*D*irect *C*urrent is called 'sticky' because it goes in one direction, and it will hold the arc a lot longer and is a lot harder to break.

Hence DC switches are bigger, have more metal, break faster and break further than comparable AC ones.

Don't assume that AC switch gear (despite its higher voltage rating) will work OK for DC. Sometimes it will, sometimes it won't. In 'no load' situation they will normally be fine, but under moderate or heavy DC load they can fail (ie melt and/or weld itself together).

Put a DC style fuse on the battery lead side ****AND**** put a 240V AC style circuit breaker in the inverter 'out' side if you are concerned about safety.
AnswerID: 29216

Reply By: ramp - Tuesday, Aug 26, 2003 at 16:27

Tuesday, Aug 26, 2003 at 16:27
hi kev,16mm is the what i would use over that distance as i think you have a 60 amp fuse on your inverter or they might of put 2x30 amp fuses on it.the reason for a fuse is not only to protect your inverter but to have a fuse blow so as your wires are protected. a 40 watt light will pull 5amps,a small TV is 7amps.your battery is im guessing 90ah therefore if you somehow manage to load your inverter fully with appliances. 10mm cable is more than over loaded.so yes as you say your only going to use lights/radio etc 6-10mm is capable of handling the job, but it is not sufficent if for some reason you are pulling max current 90amps,so we need to make sure the fuse will blow first. cheers
AnswerID: 29221

Reply By: Member - DOZER- Tuesday, Aug 26, 2003 at 16:31

Tuesday, Aug 26, 2003 at 16:31
Gday
Went around oz with an Inverter under the rear seat to power the lights in the van (and Telly).
It is not advisable to lengthern the incoming leads, because voltage drop infront of the inverter will shut it down prematurely
Similarly, a fuseable link will cause VD and thats why the factory leads dont have one.
I got around this by putting the second battery besides the cargo draws behind the wheelarch, and then mounted the leads straight to the battery.
If you cant mount the inverter close enough to the battery, then you will have to lengthern the incoming leads.
Using larger good quality wire should suffice, im not sure how big but there is a formula on Georges Landcruiser site if you search the web for 80 series.
The best advice i can give you is to brace any cabling you run securely, using cable ties etc and beware of/insulate any rub points/sharp corners.
If you wish to put a safety fuse inline, use two 80a fusable links (used for the alt of the 80) These will blow if a short occurs in the main feeder, and the inverter will have its own protection for smaller shorts.
Andrew
wheredayathinkwer mike?
AnswerID: 29223

Follow Up By: basecamp15 - Tuesday, Aug 26, 2003 at 17:44

Tuesday, Aug 26, 2003 at 17:44
If you put a condom over the fuseable link it will no longer cause VD!
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FollowupID: 20346

Follow Up By: Member - DOZER- Tuesday, Aug 26, 2003 at 17:52

Tuesday, Aug 26, 2003 at 17:52
Ah ok, so if the links ever blow....your not f#####
There you go- thinking outside the square wins again
Andrew wheredayathinkwer mike?
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FollowupID: 20347

Reply By: basecamp15 - Tuesday, Aug 26, 2003 at 19:20

Tuesday, Aug 26, 2003 at 19:20
ROFL!!! :)
AnswerID: 29242

Reply By: peck - Thursday, Aug 28, 2003 at 18:32

Thursday, Aug 28, 2003 at 18:32
Use the relationship P = V x I where P = power in watts, V = voltage in volts and I = current in amps. For Pin divide rating (output) by efficiency (usually around 90%). So 500w out at 240v = 2 amps (or thereabouts), Pin = 500/.9 = 556, therefore input current = 556/12 = 46 amps, use cable commensurate with this current. 16 mmsq is good for about 60 amps so seems a little heavy, 10 mmsq over this short distance should be OK.
AnswerID: 29479

Follow Up By: Kev - (Cairns,QLD) - Monday, Sep 01, 2003 at 11:12

Monday, Sep 01, 2003 at 11:12
6-10mm2 sounds fine concidering i dont intend on loading it right up.

Thanks.
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FollowupID: 20856

Reply By: Member - Nigel (QLD) - Thursday, Aug 28, 2003 at 23:12

Thursday, Aug 28, 2003 at 23:12
Jaycar sell resettable high current DC cirtcuit breakers that look to be waterproof - and lower voltage drop than fuses.
AnswerID: 29523

Follow Up By: Kev - (Cairns,QLD) - Monday, Sep 01, 2003 at 11:09

Monday, Sep 01, 2003 at 11:09
Thanks, i will check them out.

But for the time being i will just disconnect the + lead when not needed.
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FollowupID: 20854

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