Yes mate a relay will do the job, provided total current is within it's spec.

Using a normal relay,

Pin 85 goes to good earth
Pin 86 goes to ignition
Pin 30 goes to battery of your choosing
Pin 87 goes to the fuse block.

Then that particular fuse block will only be powered with ignition or accessories, whichever you wire it to.

As close as practical to the battery I'd still put a fuse or circuit breaker of the max size of the relay or cable, whichever is lower.

 

How did I know you would beat me to the punch so to speak? haha.

 

Firstly, there are others on here more qualified and experienced in electrical than me and no doubt they will chime in.

Run a power cable from your Redarc straight to the second battery in the rear. Bigger is better IMHO. Go at least 6 gauge or higher if room allows (I have 6 in mine for the same setup).

Run a power from your second battery to a fuse block as a standalone not from the Redarc. That will be constant power. Make sure you use circuit breakers or Maxi fuses as appropriate for the current draw at the battery for all connections even to the fuse block.

Run another wire from the battery to a relay then on to anoterh fuse block that is switchable with ignition as you have described. You CAN run the power off the first fuse block but remember, fuse blocks have a limited amount of maximum current so personally, I would just save the trouble and run two separate blocks with two separate power feeds from the battery. More work but cleaner and its all separate so if something happens to the first fuse block for whatever reason you still have the second lot of circuits in tact. Call it built in redundancy.

Next factor, how many amps will you likely pull through both fuse blocks and how many circuits? this will dictate overall wire size and what size relay you will need for your ignition circuits. Most of the shelf conventiaonl ones are 30/40 amp max but you can get bigger obviously.

Have a look at the threads Lee (Leethal) has written title "Electrical Wiring 101" which will help you no end.

Good luck!

 

I offered less detail so could type it quicker

 

yeah I guess I might need a bigger relay... I'm going to run a 45l Engel, rear camp lights, a couple of extra sockets at rear and a couple of USB sockets in the centre console. Oh and a compressor. Havent decided which ones will be ignition only yet though. Does the ignition wire from the ignition need to be of any gauge or will it not matter?

Thx
for the advise guys

 

No the ignition wire is just a relay trigger so doesn't need to be substantial.

All those items would be fine on a normal relay except the compressor. However... They are all items (fridge, camp lights) that surely you want running with ignition OFF, which is the whole point of having a second battery, so why run them through ignition? If they were all ignition powered (i.e. Engine running) why bother even having a second battery?

Also the compressor draws plenty of current and should only be used with engine running, so I'd normally wire that to main battery.

 

you wouldn't be running your engel and camp lights off the ignition switched supply so not necessarily. Depending on your engel it will pull 2.5 - 5 amps give or take and isn't running 100% of the time. Camp lights, if LED and depending on wattage will pull relatively low amp draw as well as your USB and extra sockets.
Compressor is a different kettle of fish. They can draw huge current and should be on a separate circuit again I would suggest.
There is no need for the ignition wire to be of any great size as it is only going to act as a power trigger to switch the relay. 3mm or 4mm automotive wire will be sufficient.

 

In regard to the compressor...because I want it behind the seats next to the second battery couldnt I connect it to that battery but run the engine when I want to pump the tyres up. As long as the voltage in the main battery is enough to trip the current through the redarc to the second battery it would all be good... right? Or am I missing something. Am trying to reduce the amount of cabling going back and forth...... and no room for second battery under bonnet with the UFI there..... (i know it can be done though)

 

If you have a redarc SBI and connect compressor to second battery, the compressor will draw more current than alt puts out at idle. So redarc will join batteries, compressor will run at normal speed, redarc will seperate and compressor (now just off second batt) will slow down, redarc no longer has load so it rejoins batteries etc etc.

This happens every 4 or 5 seconds and you can clearly hear the compressor change speeds.

No harm in it, but I'd suggest that when you switch compressor on, also have that power the override on the redarc so it keeps the batts and alt joined, but put a diode in this line otherwise the normal use of override will also turn on compressor.

Hope that all makes sense!

 

Timely thread and info guys as I'm about to move my dead second battery from the engine bay and move a new second behind the seats.

Leethal I've kept up with the wiring side of things until diode was mentioned.
What does the diode actually do and how do they do it? if that is easy enough to explain?

 

Diodes are really handy and very simple once you have the concept sorted. They only allow current to flow in one direction. A practical example might be a worklight; you have it come on with reverse lights, but can also turn it on manually. You'd find that turning it on manually will also flow current the other way and turn on the reverse lights, which you don't want. So you would have reverse light power flow to the work light through the diode, so it comes on with reverse, but if you turn light on manually the current cannot flow the opposite direction to the reverse lights. They are cheap and effective. Here's an example; under $3 for ten of them, delivered. These are 5w jobs, perfect for two different inputs into the same relay where you don't want one to backfeed into the other.

https://www.ebay.com.au/itm/262388389468

Or 10 x 10 amp ones for under $9 delivered;

https://www.ebay.com.au/itm/151646096015

Leethal, Don't think my redarc has an override. Its an old one I think..... Is there a way to 'fudge it'?

Pretty sure even the old ones have it mate, it's a small blue wire, does it have that? Two large terminals (one for each battery), a small black wire for earth and a small blue wire for the override to force it to join the batteries whether it wants to or not. You just supply a fused positive to the blue wire when you want to override it, for emergency starts, use of winch or compressor etc.

 

Leethal, Don't think my redarc has an override. Its an old one I think..... Is there a way to 'fudge it'?

 

mmm I'll take another look but pretty sure there is no blue wire. It was on the car when I bought it over 12years ago... maybe they removed it.....

Like the diode idea... just solder em on and then heat shrink them?

 

Can I pop a quick question in for Lethal please . . .
I'm guessing the diodes are directional? does current run toward the silver bar? and can they be paralleled?
sorry to butt in . . .
4Bee

 

Yes mate the side with the silver bar blocks flow, so you attach positive to the side without silver bar and you'll have positive at the silver bar side.

And if you have two 4 amp diodes I don't see any reason why you can't run a pair in parallel with a capacity of 8 amps max.

You can solder wire to the ends, of crimp terminals to them, and yep heat shrink is great. It is normal for them to get quite hot in use.

Hopefully there is a blue wire on the Redarc, that will make life a lot easier for you!

 

Leethal if you were putting in total new system auxiliary battery in rear what components and wire sizes would you use. I am about to undertake this shortly your advice would be most welcome. If you have posted this in past whats the link mate. Thank you.

 

Sid there's lots of factors that would affect the type of seperator/charger you would use, so I'll make an assumption you have a good idea what type suits you.

IF the seperator had the ability to allow the second battery to start the car in a pinch (ie the override as discussed in Flashman's case) then you'd want at least 2B&S cable to flow that kind of current.

If it was just a DC/DC charger (such as Redarc BCDC or CTek) then 6B&S would be fine. I think the manufacturers even specify 8B&S (smaller than 6). These type claim to charge the second battery more efficiently, which is great, but don't offer the ability to join the batteries in a pinch, ie for starting from second battery, or to allow it to assist in winching, which is the compromise. Of course you can wire a solenoid seperately just for these situations, depending on how keen you are, that gives you the best of both worlds.

If battery is in the rear, with dcdc type charger that should be as close as possible to second battery, with normal parallel seperator it doesn't really matter, probably more convenient in engine bay. I'd run a fuse block off second battery in a convenient spot down the back, close to battery, and run seperate fuses for say fridge, led camp lights in roof rack, ports for chargers etc, as it's likely they will mostly be down the back anyway. 8B&S would be fine to the fuse block for the vast majority of applications.

I'd run the air compressor(s) off main battery, and generally only use it with engine running (fast idle if your model has the ability), as they draw heaps of current.

Anything external (such as Anderson plugs for camper) I would use a circuit breaker, not a fuse.

If you have a particular seperator type in mind, do a search with the function in the top left and hopefully you'll find what you're after there, as there is heaps of info on here but some may be hard to find. If that doesn't help or you have more specific questions sing out and one of us hopefully will know whatever you need to find out!

 

Leethal Cheers for the explanation/lesson lol.
So with the work light scenario the switch for the work light would be between the diode and light yeah? In order for the reverse lights not to come on when work light switched on manually.

 

Not quite Chippy!

To cover all our bases we'll use a relay, just in case it's a higher current light that may be too much current for the reverse circuit.

On the relay, 85 goes to earth, 30 to battery power (fused, aux battery as you'll use it when camping), 87 goes to the new work light.

A wire from reverse (passenger kick panel; yellow with grey dots on GU, green with white stripe on GQ) goes to pin 86, so reverse will turn the light on via the relay.

Your switch takes power from same source and also goes to pin 86, however when you turn on the light manually, power will flow along there and back feed to the reverse circuit and turn on the reverse lights too.

If you put the diode after the switch but before relay, the switch won't do anything. You want to stop a backfeed into reverse, so you put the diode in the wire from the reverse circuit to pin 85, so it allows current from reverse to reach the relay, but won't allow current from the switch to go further than the relay back to reverse.

Sorry that's hard to explain, does it make sense? If not maybe I should draw a diagram and take a photo of it.

 

There's actually a few ways to skin the reverse/work light cat Chippy, have a look at this thread if you get time, there a couple of even better ways of wiring rear lights in my opinion;

http://www.patrol4x4.com/forum/auto-electrical-37/electrical-wiring-102-reverse-work-lights-333978/

 

Apologies for the off topic Flashman

Thanks Leethal, just trying to get head around this diode biz which is new to me.

Geez might have to pay you to draw up a wiring diagram for my intended set up lol

Just have to get my 12v setup/vision out of my head first and on paper!

 

Leethal, any idea if I could run a USB socket and a volt gauge from the power on the handbrake switch? I assume it only has power on with the ignition....

 

No mate, the handbrake switch is an earth switch, not power, so pulling the handbrake on and off connects and disconnects the earth.

Also the volt gauge should have its own dedicated wire to the battery it is reading, as anything else on same circuit will show a false low reading on the gauge.

 

How do I wire the volt gauge up so its only on with ignition then? Sorry for all the questions....

 

Do it through a relay.

Pin 85 to earth
Pin 86 to ignition feed
Pin 30 to battery you're reading
Pin 87 to guage

That's as direct as practical, and will just show you voltage with ignition on.


Ask as many questions as you want flashman, hopefully anything I don't know someone else will!

 

Do it through a relay.


Ask as many questions as you want flashman, hopefully anything I don't know someone else will!

much appreciated

 

Leethal, calling on you again...... I'm always looking for a wire to tap into for 'ignition on'. I thought I found the major one from the ignition switch (White with a pink or red stripe) but my voltmeter has carked it and keeps telling me no voltage when I know there is. So i've had to temporarily tap into one that I've used before (behind the clock). Looking for a more permanent solution so was thinking:

1. Tap into the main ignition one (which one is it?)
2. Run it to say a 70amp relay
3. from there into a Narva fuse box.
4. Run everything from there

Wot you think

PS I got my voltmeter etc running
http://http://www.patrol4x4.com/forum/general-patrol-discussion-17/replaced-pen-holders-337649/#post5351145

 

Couple of options for ignition feed, one is from wiring for wiper motor if you want one in the engine bay, or if inside the dash area I'd go for an ignition feed in the wiring from plug at the side of the ignition barrel, on GUs I'm 99% sure from memory it's the blue wire.

Depending what you want to run with ignition on, a 40 amp relay should be fine, and is far easier to source than a decent relay capable of handling more than that. Next step up is more likely a solenoid to be honest.

I've recently tried a relay rated at 80 amps on another fella's car, he was only drawing 40 amps and cooked two of them within a few days, learning experience for me as I hate having problems on other people's cars. No good deed goes unpunished...

Hope that helps!