240v hookup / 12v LB - what feeds what?

[Moseley]

Hello folks, and a happy new year!

I've begun the task of tidying up the PO's electrics, as although everything seems to be suitably rated, a lot of domestic cabling had been used and it generally is an untidy mess.

So, everything is stripped out from the LB side of things and I'm working out what will be hooked up to it and sizing the cables and fuses accordingly. The current setup is all running off a split charge relay and LB so that won't be too hard to plan out. Off the top of my head we have:

1. Propex
2. Stereo
3. External amps
4. Lighting
5. Inverter
6. USB sockets

Now then, in the future, we plan to add in a fridge and a 240v hookup. Now bear in mind I'm not an electrician, but my understanding with this is that the 12v and 240v systems have to be separate - you can't just wire for instance a 3 pin plug socket into the inverter and also the 240v hookup without some sort of switch to change between the two electric sources?

If I'm on the right track so far... the 240v hookup would be wired into a trickle charger so as to effectively power the 12v side of things off the LB. However, the trickle charger is not going to produce enough current to maintain the battery whilst also powering everything, so how does it all tie together? I've read about Zig units, but just wanted to get my head around the basic wiring first!

Any pointers would be much appreciated as I get to grips with this dark art... :msn4:

 

[jonboylaw]

I would advise fitting a double socket powered by the hookup and a single socket to the inverter for simplicity. That way you can avoid plugging the kettle or hair dryer into the inverter powers socket.

Other than that wire as follows. LB to new fuse box. One of the feeds connected to the trickle charger with a suitable fuse. The charger should take a 5a feed from an RCD unit. The other RCD circuit should be something like a 10a that feeds the double socket. You want to ensure the van Breakers trip before the hook-up pole does to avoid tripping the site supply.
The feeds for the inverter, stereo, amps, lights and Propex can then be taken from the LB fuse box with suitably rated fuse and wiring ( fuses always less than wiring please).
Also ensure you ground the hookup and sockets really well. You really don't want to risk an un earthed 230v supply.


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[Moseley]

So basically the 240v hookup supplies the separate sockets, and the trickle charger to maintain all the 12v items? I suppose my only query is what happens if the current draw on the 12v side outstrips the trickle charger. For instance, the amps are about 400w RMS, which by no means are as big as I'm sure some people run! So at RMS power they'd be looking at about a 32A draw which is way more than the trickle charger (about 4A from memory).

Presumably other people must use equipment that'd draw more than a trickle charger can supply - is it just a case of hoping that you only use these items for a period of time that means the LB drains, but doesn't go completely flat?

Making more sense now!

 

[jonboylaw]

Your leisure battery acts like a large reserve, you wire the fuse box to the LB and the trickle charger to the LB to provide top up. When you have your stereo running you will deplete your battery reserve over time, so yes the trickle charge will not keep up with heavy current draw, but a 110Ah battery will run a stereo for a few hours.


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[Moseley]

Your leisure battery acts like a large reserve, you wire the fuse box to the LB and the trickle charger to the LB to provide top up. When you have your stereo running you will deplete your battery reserve over time, so yes the trickle charge will not keep up with heavy current draw, but a 110Ah battery will run a stereo for a few hours.


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That makes sense. I guess that despite calculating all the cabling / fuse ratings for the max current draws, in reality, the average consumption is probably a small fraction of what everything is rated for, and the LB reserve is probably never even used.

I guess I can crack on with wiring up the 12v bits and then look at sorting the 240v stuff at a later date. Looks like I'm going to need a shed load of cables!

Cheers for the help!

 

[rickyrooo1]

if you use a ctek or suchlike charger to top up the battery you have no issues as you can use it on "supply" setting, I've never had a problem

 

[Moseley]

if you use a ctek or suchlike charger to top up the battery you have no issues as you can use it on "supply" setting, I've never had a problem

I've got an Aldi trickle charger that is used whilst in the garage to maintain the LB. I'm not sure that it offers the same functionality of a CTEK; it is either displaying battery voltage, or topping it up, nothing more.

Got a fuse / cabling question to add to this to save starting another thread. I'll use the example of my head unit which will be running from the LB. It is rated at max power output of 200W, which gives a 17A current at 12v. However, it has an in-built fuse of 10A. Hopefully someone can confirm that it is ok to presume that there is no need to select no bigger than a 10A fuse and suitably rated wiring? Also, does anyone know why the manufacturer would use a lower fuse rating current than potentially the head unit could supply?

Another example I could use would be the sub amp. This is rated at 800W max, which gives 67A. However, manufacturer recommends the use of only a 40A fuse...?? I know that the fuses are there to protect the wiring, but surely the amp could draw enough current to pop the fuse? All the other bits that will be wired in, I've assumed worst case scenario and have sized fuses / cables to suit the max current draw the item could draw, so just wondered why in particular the audio items seem to offer different guidelines.

I think I'm being way too over-cautious but I'd rather understand these things!

 

[jonboylaw]

Audio power is measured as Root Mean Squared so 200w RMS, which is about 2/3rds of what it sounds like. Just a marketing tag.


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[Moseley]

Audio power is measured as Root Mean Squared so 200w RMS, which is about 2/3rds of what it sounds like. Just a marketing tag.


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They are the max quoted powers, rather than the RMS figures though? It makes it look like the max power from head unit / amp could never be achieved, as the internal / recommended fuses would blow before then... not sure if I'm missing something. Obviously it's no issue downrating the fuses / cabling to suit the manufacturers recommendations as I doubt I would ever need to run them anywhere near full volume, but just wanted to understand why the difference.

 

[jonboylaw]

Check the spec, I expect they are using max RMS power. This would give:

200w x 0.707 = 141.4W
141.4/13.8 = 10.25A

Anyhow, if they have a 10a fuse on the supply then you could use a 12 or 15A fuse in the box as you really want to protect the wiring from shorts.
If it is a 10A fuse on the output stages (to the speakers) then this is a different kettle of fish.

In this case P=IsquaredxR
Assuming a 4 ohm load:

P= 10x10x4
= 400W


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[Moseley]

Check the spec, I expect they are using max RMS power. This would give:

200w x 0.707 = 141.4W
141.4/13.8 = 10.25A

Anyhow, if they have a 10a fuse on the supply then you could use a 12 or 15A fuse in the box as you really want to protect the wiring from shorts.
If it is a 10A fuse on the output stages (to the speakers) then this is a different kettle of fish.

In this case P=IsquaredxR
Assuming a 4 ohm load:

P= 10x10x4
= 400W


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Hmm, pass to be honest. It doesn't state it in the manual, but that's not to say it isn't.

Ah well, I'll go by what the manual recommend. Cheers for the help! 8)