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Joined: Jun 17 2018
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Hiya Chaps!

I've heard of a good few peeps who have a T-Maxx duel battery set up on their P38.

2 things i've been wondering is..

Where does the 2nd battery go?

And How does it in a nutshell get wired into the vehicle?

AND is it for prurely accessory purposes or can it be used as a backup to the main battery?

Cheers H!

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Joined: Jan 05 2016
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Marty will be along shortly with some details on his install I'm sure - he went with the TMax setup and has spent about 3 years trying to persuade me to do the same...

And admittedly I relented not long ago and put in a similar but more basic setup. With the tMax you can manually as well as automatically link the batteries - great if you need to give yourself a bit of a jump start (though why? The battery should not be going flat unless left a pretty long time unless you have a problem that needs fixing).

My setup is a standard voltage sensitive relay setup to charge my second battery, which is then used exclusively for powering other things like my fridge etc. I think I have a thread on here about it.

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Joined: Dec 30 2015
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If you've got a decent battery and aren't running other things, like Sloth with his fridge, then there isn't a lot of point. Being ex-plod, my car still has the split charge relay and cables to the boot area where the aux battery used to live, but that was to run lots of lights on the roof, etc, the car battery runs the car, that aux runs the other stuff..

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Joined: Jun 17 2018
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Thanks Gents.

I want to add a LR cooler in the boot aswell as spots.

She goes/went off road quite a bit so lights are a rather big requirement especially on the farm, in the winter!!

a good few "mods" i want to do and I thought it prudent to add this system.

Cheers Gents.

H

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Joined: Jan 05 2016
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Lighting shouldn't really be an issue for the alternator alone - I think the smallest was a 120amp unit, biggest being the 150amp on the Thor engined models.

I've modified my BECM so when I flash the head lights, the fog lights also come flash. They come on if full beam is selected too.

On top of that I have an electric fan that draws about 30amps running on low speed, and the electric condenser fans are now configured to run at high speed when the AC compressor is engaged - otherwise low speed all the time the AC is 'on'.

And at some point I'll be fitting my nudge bar with another pair of halogen spots.

But a fridge of any kind... if you want to leave it running with the vehicle not running itself - is best done from an auxiliary battery for sure. I used to leaev my compressor Waeco fridge running from the main battery and it would be okay for a day, maybe two at a push, when the battery was new. Engine would still start.

Now I don't need to worry about it and it'll probably go for longer on a battery being used just for that. If it does run flat, the worst that happens is the fridge stops working. A peltier or TEC type fridge will run for far less time on either setup though as they draw a constant 4-5amps instead of stopping/starting like a compressor fridge.

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Joined: Dec 30 2015
Posts: 1997

Of course... if you have converted to LPG you could have a go at an LPG powered fridge!
Well, maybe. I'm not sure how they work!

PAGING SIMON!!!! Simon to the LPG Phone please :)

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Joined: Dec 30 2015
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As Sloth mentions... I've got the T-Max setup in mine.

I've fitted the battery on the RHR side of the loadspace and made a cover for it. I've got I think Twin 25mm2 cable running back to front, with the positive fused at 250A at each end through a mega fuse.

The digital T-Max setup will link the solenoid for charging both batteries when the engine is running and charging voltage is detected. It automatically disconnects the 2 batteries about 30s after engine switch off.

I have an Anderson connector in the boot for my jumper cables, and I run the rear accessory socket from the auxiliary battery too so it's permanent 12v. Good for charging phone etc when I've camped in the RR as no need to have the ignition on.

When I had 2 EAS compressors I ran the second one from the auxiliary battery too, with a trigger wire from the main one. Meant if I wanted to run a compressor for testing EAS etc with the engine off, I could unplug the one in the EAS box and run the second one off the other battery without draining down the main battery.

Sometimes if I'm doing a load of electrical work in the RR and have the radio on etc, I'll manually link the batteries so I don't run the main one down.

Once I've got my A into G and bought a winch to fit in the factory winch tray, then having the second battery will hopefully help with the oomph for that.

I managed to fit the twin cable in the RH sill with the other cable looms and through the firewall, under the fuse box and to the solenoid which is mounted on the back of the battery tray/ECU box.

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Joined: Jan 16 2017
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Morat wrote:

Of course... if you have converted to LPG you could have a go at an LPG powered fridge!
Well, maybe. I'm not sure how they work!

PAGING SIMON!!!! Simon to the LPG Phone please :)

Thats usually called a caravan on the towbar

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Joined: Nov 16 2016
Posts: 1014

BrianH wrote:

Morat wrote:

Of course... if you have converted to LPG you could have a go at an LPG powered fridge!
Well, maybe. I'm not sure how they work!

PAGING SIMON!!!! Simon to the LPG Phone please :)

Thats usually called a caravan on the towbar

Possible... Good points are gas consumption is economical, work better (when level, i.e. not parked on a steep hill) than a thermo-electric fridge, no flattening of batteries to worry about. Bad points are you've got a flame inside the car, it would need an exhaust flu to prevent gassing vehicle occupants (with engine off / ventilation off) so that's a hole in the roof or side of the car, usually need to be level to work properly (though some fridges are much more forgiving than others in this respect), the flu's can lead to the flame being blown out in wind/while driving (some setups seem much better than others in this respect too). Best practice is to fit the fridge with not only an exhaust flu but also it's own intake air setup (hole in the floor under the flame), the LPG tank would need modding to have a vapour take-off fitted to run to a manual shut off valve to the regulator to the fridge.

Would usually be a caravan type fridge but freestanding 240/12v and gas fridges are available (I've always had one). The freestanding type aren't meant to be ran on gas in confined spaces, no easy way of connecting to a flu.

I do fit vapour take-offs on autogas tanks, as part of the setup I insist that I supply and fit the gate valve and regulator (both external) running a length of pipe from the regulator to where the customer needs (usually the gas inlet for their campervan). On most installs I fit the gate valve so it can be accessed by reaching a hand under the vehicle. To fit the vapour take-off (on external autogas tank) I drill a 3mm hole in the top of the tank, cut a 'hidden filler' boss in half (leaves a steel hexagonal pipe with 8mm pipe compression fitting, total length about 20mm), grind the hex down so it's round, weld it onto the tank over the hole, fit a cut down/shortened 90degree fitting into the compression fitting and run pipe (copper or Faro) from this to the gate valve which is fitted directly onto the regulator. I shouldn't really be modding/welding tanks but it is safe when the tank is external, could be safe internal if I came up with a way of fitting a gas tight housing around the mod (wouldn't be too difficult). This way there's only a 3mm hole in the tank (so if the worst happened and the fitting came off it wouldn't be toooo bad) and since the internal area of the fitting is only about 8mm diameter (50sq mm / 0.1sq inch) there'll only be around 30pounds pushing against the fitting/weld if the tank sees 20bar pressure (reckon the weld would be good for about a ton).

Recently bought a thermo-electric heat pump type fridge from Halfords to slot between the front seats on long trips, it will keep stuff cool if it's cool when it goes in but takes an age to pull temperature down if stuff isn't cold when put in. Will only cool to about 15degC below ambient temp, OK in an AC cooled car and only draws 6Amps at 12v. An electric compressor type would be a lot better, or would be possible to tap into AC lines and fit another evap in an enclosed box to make a very powerful fridge that would obviously only work with the engine running... I thought about doing this when I recently had AC problems and had to change my engine, would have been the ideal time to fit it, but in the end I just wanted to get the car running again.

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Joined: Jan 05 2016
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Compressor fridges are the way to go :) Waeco/Dometic are basically the defacto name to go for here. ARB are popular in the states I think.

I have a Waeco CDF-45 and have on a couple of occasions accidentally turned cans of pepsi etc into slushies...

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Joined: Feb 25 2020
Posts: 209

Though useful to resurrect this great topic to ask some details to get acquainted on how you guys done some of these mods, some of them in my mind since long time. I am gearing up to make some wiring to bring "powerful" 12V to the rear and also to run the condenser fans in the proper way...I start by the 12V to the rear ... my plan is to run а wire, or wires, to power the portable winch on the trailer, so I can ditch the drag of bringing along a dedicated battery... my idea was similar to Marty's, now it will be very similar if not identical ...

Any suggestions to the "megafuse" (how much? max winch draw should be in the 200A region). I have good thick gauge wiring so that is covered (from our scrap Audis which had the battery under the rear seat), the P.O. already made some holes in the firewall I will reuse, and my idea was to arrive to the rear, to a a connector like this:
https://www.electricwinchshop.co.uk/400-amp-snap-connectors.html

and from there on to the winch when needed, or also to have a set of mobile jumper cables (want to do this also for the front, from the main battery). Was thinking to splice and run another wire from the connector (with a separate 40A fuse) to the spare wheel well, to put there the air compressor. Electrically, would this be a good idea? This is to avoid using the left 12V "permanent" which Marty mentioned is max 20/30A thru BeCM ... and to avoid running another 5m of wire just for the compressor ...

Next question: what to do with the ground? Can I safely run it to someplace in the body or  chassis around the trunk area (where?) or is more advisable to run back another (thick) wire back to the - terminal on the battery?

Well, this became longer than expected but if you guys still with me, my next item is to address the manual control of the condenser fans, following upon what Sloth did. In my darkest times overheating the engine, out of desperation I made a bridge with a cable in the AC pressure switch by the radiator, and with a "flying" manual switch in the dash I was able to run the fans, but I am unconvinced this is the safest option ... looking for ideas to make a more permanent arrangement, maybe getting the direct signal for the fans from the fusebox instead of messing around with the AC system?

And so it begins ... got plenty crazy ideas to turn mine RR in a more versatile and usable platform :-)

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Joined: Dec 30 2015
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Run two cables front to back, don't rely on using ground. At the sort of current you are drawing even the tiniest bit of resistance will have a big effect. I've still got the two cables running to the boot from where plod had an auxiliary battery in the RH side of the boot. In fact, it might be better if you run two cables and have a secondary battery in the boot rather than risking your vehicle battery and alternator.

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Joined: Feb 25 2020
Posts: 209

OK, you mean to use the aux battery as a "buffer" ... makes sense. I was planning it all along, but thought just of running the cable(s) now and leave that option open for later, to save time effort and some expense ... well better do it once and proper then.
Will update when I get something done.

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Not as a buffer but as a supply to run your extras from. Think about it, if you try to pull 200A to run your winch from the vehicle battery, you'll flatten it in no time meaning you won't be able to start the car. If you try to do the same with the engine running you will be drawing more than the alternator can supply (either 100, 120 or 150A depending on which alternator you have) so could burn out the alternator. So have a second battery, charged through a split charge unit when the car is running but disconnected when not. Use that to power your winch with the engine switched off so it isn't connected to the vehicle battery, but if it starts to go flat, disconnect the winch, start the engine and run that for a while to put some juice back into the secondary battery.

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Joined: Dec 30 2015
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If the engine is running, you will have the max capacity from the alternator, plus whatever current capacity the battery has in it at the time. Yes, it will take a decent load off the main battery when you're running the winch - but then the alternator will re-charge it once the winch load is removed.

If you had say a 100AH battery (to keep the example easy) it in theory could supply 100A of current for 1Hr before being completely discharged. Again (loose) theory says if you drew 200A from it, then it would last half the time - so 30mins. Whilst the battery would obviously not be the happiest about it, and in reality it wouldn't work like that - and you would have the engine running - so some power coming from the alternator - a winch would be fine on a single decent battery.

In fact none of the LR accessory fitting specs for the winch tray show fitting another battery or the need for it. For occasional winching the standard setup would be fine.

If you have a split-charge system and 2 batteries, then you're just upping the capacity - less stress on the complete system, and you'd be able to winch for longer if necessary.

As an example a Warn Zeon 10s 12V winch specs (from here: Warn Winch show that just running the winch with no load will draw 62A, and at full load will draw 409A. Given that's a 10000lb / 4536kg rating for the full load, you're never likely to pull that much - or if you do because something is really stuck, it would be for a short period. And if you were really stuck - you'd probably use a snatch block to double the line and make it an easier pull for the winch in the first place.

I added the second battery to mine with the view to fitting a winch in the factory winch tray that I got my mitts on awhile ago - and also to run other accessories like (now) my inverter and also the EAS compressor runs off it, so I can run that without the engine on and without draining the main battery.

If you're planning on making it so you can put a winch at the back of the vehicle, then having the second battery there gives you a good place to hook into it, and means you can probably do light winching without having to have the vehicle running - if it's a beefy enough battery!

I put my split charge system in with 230A (from memory it was over 9 years ago now) twin (+ve/-ve) cable from the engine bay to the loadspace. The +ve feed is fused at each end with a 200A (again from memory - might be 250A) mega fuse.

I think Sloth fitted his VSR/second battery with just a +ve run and then attached the -ve back to the chassis somewhere at the back. It's definitely more than capable of handling the current. I just ran twin cable in mine as it wasn't that much more expensive, and at the time I had all the looms out of the sill on the RHS, so was easy to run them in at the bottom and then lay the vehicle looms back over the top.

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I did indeed run a 16mm cable down out of the body through grommet under the tail light and bolted it through the rear cross member. I have a 16mm cable running front to back fused at 100 amps both ends for the positive supply, with my VSR in the back too. My setup is only to keep a leisure battery charged in the back for the fridge and other connectable things - hence I didn't go for the Tmaxx or chunkier cabling. I've seen it pull 70 amps thus far - haven't had an issue with voltage drop or the battery not getting a good charge thus far.

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Joined: Feb 25 2020
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Thanks for the food for thought - might indeed be a good idea to proceed in the direction of a split charge + 2nd battery.
Marty, I did forget the inverter ...another thing to add :-)

Sloth, how did you wire the manual control for the fans? I wrote some post above how I did it so far, but I am unconvinced is the way to do it proper ....

Thanks again for the great inputs!

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Joined: Feb 25 2020
Posts: 209

Uh I forgot to mention the winch I use to haul up the dead on the trailer is a Warrior Ninja 4500lb. Yes, it is no Warn M8274, but on the other hand with the synth rope is fairly easy to carry and hitch/unhitch from the trailer, must be like 30 pounds.
I believe its max draw is 200A, and that is my reference point for my calculations.

With the bak-rak adapter and plate, it is easy to use on any 50mm towball. Nice piece of gear, the bak-rak (clever and British, you guys should be proud!). And easily adaptable for rear mount (if you have a tow hitch, which most have), or front (if I ever get to make or get one, like the one offered by Florent/RR Evolution)
https://rr-evolution.com/epages/e53aa5b9-2253-44ee-816d-684d89c8af19.sf/fr_FR/?ObjectPath=/Shops/e53aa5b9-2253-44ee-816d-684d89c8af19/Products/PMTA

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I believe Richards caution is wise. Eg, if you try to draw 200A from a 150A alternator, I think the alternator will try to supply 200A even though it won't be able to, and you risk burning the alternator up. If you are only at idle, the alt may not be turning fast enough to burn itself out, so you may be okay. Having said that, I see people using their winch with the engine running reasonably often, so the danger might not be that high.

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Joined: Dec 30 2015
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Just had a look at the winch spec, and yes, 200A is the max current draw for that winch. But that is at full line capacity of 4500lb or just over 2T... Which is nearly pulling the dead weight of another p38.

If you're pulling something that's still rolling, and not dragging a dead weight then the load will be a lot less, and so will your current draw.