Ignition live for 500w inverter?

[Wilsont61]

Hi all, new here

I’m a joiner and trying to rack my van out for the trade.
I’ve bought a 500w inverter. I’d like to use it to charge the odd battery, but only while the ignition is running to prevent the battery draining.

I don’t want to spend more money on additional batteries and dc-dc chargers etc.

How do I go about hooking something like this up, in the back of the van?
I have somewhat limited knowledge of electrics by the way, so any advice is very much appreciated

Thanks

 

[roadtripper]

Your challenge is going to be the ignition live aspect, there are a few high current options under the seat in standard wiring but nothing ignition switched.

A 500w inverter is going to be about 50A draw on the 12v DC side.

Anything over 30A is non trivial electrical work as a rule of thumb, not an ideal starting project.

Realistically you're going to need a high current feed from the starter to the rear of the van and a chunky ignition switched relay to turn it off when the van turns off - and that essentially is a basic split charge leisure system just minus the battery.

 

[Wilsont61]

Your challenge is going to be the ignition live aspect, there are a few high current options under the seat in standard wiring but nothing ignition switched.

A 500w inverter is going to be about 50A draw on the 12v DC side.

Anything over 30A is non trivial electrical work as a rule of thumb, not an ideal starting project.

Realistically you're going to need a high current feed from the starter to the rear of the van and a chunky ignition switched relay to turn it off when the van turns off - and that essentially is a basic split charge leisure system just minus the battery.

I see, I don't really want to go down that route.
Reading the manual for my inverter, it comes with a 12v cigarette plug and states you shouldn't pull more than 150w using this plug. I'm sure there's a calculation for the watts and amps, but apparently the DeWalt charger doesn't pull much more than 8 amps so I for sure don't need anything over 30 amps let alone 50.

Is there a way to prevent said inverter from pulling more than 150w?
I could potentially use one of those piggy back fuse holders into the fuse box, I'm assuming a 10amp fuse would suffice and protect my van?

Really appreciate the help by the way! Thanks.

 

[roadtripper]

As a rough rule of thumb with inverters divide the watts you will use at 240v and that will be the amps used at 12v

A normal cigarette lighter style socket should only be used to draw 8 amps continuously for something like your charger situation otherwise they overheat. Given efficiency losses that's around 100w

The thing with van electrics you must size things for the maximum use case. You may know you will never plug anything over 100w into the inverter but the mate helping you might not. Pull 50A over a cable sized for 10A under the floor of the van and you're going to have a fire and will have a tricky time with insurance if it was something you fitted.

You could piggy back off an ignition switched circuit in the front fuse box and down rate the fuse as you suggest but there is a chance you may regularly blow the fuse with the start up surge of the inverter. Given you still need to route a wire from there through to the back you may as well route through a chunkier cable from the battery.

An alternative might be to leave to one side the ignition switched aspect. Not sure if you are a T6 or a T6.1 but there is often a reasonably high current feed to the electrics under the passenger seat. It might be possible to add a 50A Anderson connector with an inline fuse around 30A and then have a matching one on the inverter. Then you can plug it in when on the way to a job.

Third alternative might be to get a basic 240v power back type battery. That needs no work on the van electrics at all and can be charged overnight at home off the mains and should give plenty of charges of your tool batteries.

 

[Wilsont61]

As a rough rule of thumb with inverters divide the watts you will use at 240v and that will be the amps used at 12v

A normal cigarette lighter style socket should only be used to draw 8 amps continuously for something like your charger situation otherwise they overheat. Given efficiency losses that's around 100w

The thing with van electrics you must size things for the maximum use case. You may know you will never plug anything over 100w into the inverter but the mate helping you might not. Pull 50A over a cable sized for 10A under the floor of the van and you're going to have a fire and will have a tricky time with insurance if it was something you fitted.

You could piggy back off an ignition switched circuit in the front fuse box and down rate the fuse as you suggest but there is a chance you may regularly blow the fuse with the start up surge of the inverter. Given you still need to route a wire from there through to the back you may as well route through a chunkier cable from the battery.

An alternative might be to leave to one side the ignition switched aspect. Not sure if you are a T6 or a T6.1 but there is often a reasonably high current feed to the electrics under the passenger seat. It might be possible to add a 50A Anderson connector with an inline fuse around 30A and then have a matching one on the inverter. Then you can plug it in when on the way to a job.

Third alternative might be to get a basic 240v power back type battery. That needs no work on the van electrics at all and can be charged overnight at home off the mains and should give plenty of charges of your tool batteries.

Thanks! I didn't even know about the one under my seat! Thinking about retrofitting some heated seats from this now haha.

I've attached what's under my seat
And assuming this is what I'd need: link

What would be the neatest way to tap/splice into this? - Also potentially a stupid question, but am I right in thinking I should disconnect my battery before cutting into anything?

I'm unlikely to remember to unplug anything and most likely going to drain my battery. Is there any way of doing this while the ignition is on?