discoBizz
Member Since: 20 Sep 2008
Location: Manchester
Posts: 1416
  
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| Adding a switch to power an inverter |
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Hi all,
am thinking of fitting the inverter I have sitting in the shed over the next few days. One thing I'd like to do is add an on/off switch (my model doesn't come with a remote switch) somewhere close to where the outlet is going to be (the inverter will be tucked away, probably behind the left boot panel).
Is it just a case of a switch and relay to provide power to the inverter from the YT aux battery? Or is there/should there be any circuitry to gradually power it up?
Thanks! ==> Guide - Inexpensive AV Modification
==> Guide - Extend the multimedia of your Discovery III (September 2011, v1.2 uploaded)
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 20th Jul 2010 9:49 am |
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heine
Member Since: 07 Feb 2007
Location: Midrand
Posts: 4054
 
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Straight on off should be OK
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| 20th Jul 2010 10:07 am |
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heine
Member Since: 07 Feb 2007
Location: Midrand
Posts: 4054
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I guess that depends on the size of the inverter , I only had a 300 watt and it never drew more than about 3- 4 amps
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| 20th Jul 2010 12:14 pm |
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methley
a.k.a. Big Hairy Ski Monster
Member Since: 07 Oct 2008
Location: Marshfield, South Glos
Posts: 2433
 
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Biz, 1500w peak is 125A at 12v! At that's assuming the inverter is 100% efficient, which it won't be. I'd strongly suggest ensuring all your wiring and switch gear is sized to suit. Andy
Fridge Slide for sale https://www.disco3.co.uk/forum/post2064622.html#2064622
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| 20th Jul 2010 12:23 pm |
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discoBizz
Member Since: 20 Sep 2008
Location: Manchester
Posts: 1416
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Thanks Andy. A little more confused now however: the 600w (1500w peak) is the AC output power, not the input... which is more than plenty for the intended use (the highest draw would be about 200w).
But the question is fitting a switch to isolate the input current from the aux battery to the inverter input (which only states <0.5A when idle). Are these two specs related?
Wiring wise, I've gone for AWG 7 (10mm2) cables which should be plenty? (in fact the supplied cables with the croc clips don't look even half the thickness) ==> Guide - Inexpensive AV Modification
==> Guide - Extend the multimedia of your Discovery III (September 2011, v1.2 uploaded)
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| 20th Jul 2010 12:37 pm |
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methley
a.k.a. Big Hairy Ski Monster
Member Since: 07 Oct 2008
Location: Marshfield, South Glos
Posts: 2433
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Hi Biz,
The inverter merely converts from 12v DC to 240V AC. The power specification of the output is directly related to the current draw on the 12v side. i.e. if we take 600W as the example, then that's just 2.5A on the 240v side. However, you still need to feed it with the same power on the 12v side. 600W at 12v is 50A.
In practice it will be more than 50A as the inverter is not 100% efficient at the conversion (some power will be lost as heat).
The idle figure is irrelevant when sizing your cable and switches. You need to cater for the MAXIMUM possible current draw based on the specification of your inverter.
The current draw will vary according to the load you place on your inverter, but always cater for the maximum values to avoid overheating and burnouts. Andy
Fridge Slide for sale https://www.disco3.co.uk/forum/post2064622.html#2064622
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| 20th Jul 2010 12:44 pm |
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Navigator
Member Since: 17 Mar 2010
Location: Stay at Home. One of the lives you save could be your own.
Posts: 5105
  
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Just to muddy the water further - the instantaneous startup current can be greater then that required for the maximum rated load. Often a "slow-to-blow" fuse is used - it can handle a higher current for a very short time. Also, the switch contacts have to be capable of handling this short higher load without arcing - so use a relay.
"If in doubt - use one size up!" A vaccine does not stop you catching a virus, or passing it on, or getting ill from it, really ill. It does reduce the likelyhood of you dying when really, really ill. Stay Alive - KEEP AWAY FROM PEOPLE.
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| 20th Jul 2010 1:03 pm |
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Navigator
Member Since: 17 Mar 2010
Location: Stay at Home. One of the lives you save could be your own.
Posts: 5105
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I myself would start from what I wanted to do; only go for 250v AC if it cant be achieved at 12v DC; then look at what current is needed at 250v; then specify the inverter size; add 20%; then build to that spec.
The efficiency of inverters is usually not linear - getting an extra 5 amps AC out requires much more DC in than getting the first 5 amps AC. Are you sure you cant fulfill your needs using 12v DC? A vaccine does not stop you catching a virus, or passing it on, or getting ill from it, really ill. It does reduce the likelyhood of you dying when really, really ill. Stay Alive - KEEP AWAY FROM PEOPLE.
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| 20th Jul 2010 1:19 pm |
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discoBizz
Member Since: 20 Sep 2008
Location: Manchester
Posts: 1416
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Point taken Navigator...
All started when the Sony laptop charger blew the humble APC 150w inverter I had (it uses 19.5V @ 4.7A which should have been enough but hey-ho) and then evolved into a (need) want to power other existing appliances...
I guess I could revisit the family needs (only ever used on holidays anyway), but doubt the cost of getting 12V DC equivalents for all that are deemed "necessary" would beat that of an inverter...
Many thanks again for all the help  ==> Guide - Inexpensive AV Modification
==> Guide - Extend the multimedia of your Discovery III (September 2011, v1.2 uploaded)
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| 20th Jul 2010 1:50 pm |
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Would that imply a max 25A before blowing the fuses?
