twin battery set up wanted

[Davey Boy]

Two batteries in series for better starting in cold conditions. You get it on jap import trucks to cope with the cold Japan winters. Some of the systems will possibly be 24V. Once one battery goes it drags the other one down.

They were parallel in the Paj. It's a standard winter pack on imports.
When like this, it's really important to have both batteries identical so they charge and drain together, as one big battery really...

I think my custom kit from ALM cost about £100 all in.
My split charge system has proved itself in some pretty hostile terrain abroad. I'm really happy with it, I rely on it all the time, not just when we're at altitude, in the Alps.

As said, cable and fuse ratiing are critical, based on your batteries amps and what you intend to use them for.

 

[melissachels]

My surf Is dual battery & you've got not a chance of starting it off 1 battery, other than that I'm lost.

I will be looking to do a dual battery system with a 2nd alternator off the ac pulley cos my winch is 24v.
Now that'll be a learning curve...Don't like electrics.

I don't like or use ac ever cold & flu harbourer if you ask me.

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[solarman216]

Mel my darling, if you have 24v winch then you really need a separate 24 volt system ie two more 12v bats in series, and a 24 volt alternator, there is no way you can run this set up from 12v alternators, Rick

 

[Lazy-Ferret]

Well fair point clive but surely people do fuse the cable that effectively bridges the two batteries? If you stick a 10amp fuse in the cable it will simply blow if the starter tries to pull juice from the second battery. I have also heard of people fitting diodes between them to stop current flowing back out of the second battery. I just said 10amp as an example but you get the idea just the same.

I personally don't like those auto sensing units, I've seen them fail and flatten the main battery twice. Not on my vehicles too. It's only my opinion based on experience that I have seen. I know others like them and that's their personal choice.

Good idea having a volt meter monitoring the condition of the batteries though.

By the way Rustic has a great idea, he has a nice thick cable with an old starter solenoid and a switch inside the cab. That way he can give the main battery a boost when starting in difficult conditions. Liked that idea since he mentioned it, apparently he's had that for over twenty years on his truck:augie


By the way Clive, what do you use to trigger your relay?

On my car I used a proper voltage sensing one for split charging circuits (forgotten the name at the mo, but expensive Ducol?), but because of the issues I mentioned, on Suz's I used a 200amp relay which is switched by a smaller relay off the back of the alternator lamp feed. The smaller relay also switches some other accessories that I don't want on unless the engine is running.

I agree on the fuse blowing, but it is going to be annoying if you keep blowing fuses, especially when you are only really going to notice when the second battery is very low most of the time.

The lead that runs between the batteries is fused at both ends just incase the feed wire should get damaged. I have inline 150amp maxi fuses.

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[Barrbeast]

They were parallel in the Paj. It's a standard winter pack on imports.
When like this, it's really important to have both batteries identical so they charge and drain together, as one big battery really...

Yep parallel is what I meant :doh

 

[jims-terrano]

Some interesting ideas and thoughts about this subject.

How does the sensing circuit work taking a feed from the alternator light wire. Surely the light is only on when ignition is turned on and then goes out when the engine starts. No I know a relay can be open or closed circuit when enrgised or not, I get that that's no problem. But taking a feed that breaks the circuit when the light is on, but surely this will make the circuit when the light goes out. The light is also out when ignition turned off?

 

[Davey Boy]

Yep 150 mega fuses for me to.
Incidently, my intelligent relay has an optional starter assist function should your primary battery get a cold and struggle to crank the engine.
The relay will sense the voltage drop and temporarily use the power in your leisure battery to help start the engine.
An intelligent relay is called this because it switches charging from the alternator between the two batteries while driving as it's always reading the voltage on both. It's priority though is always to satisfy your main cranking battery.

For info. I'm running 95amp cranking and 120amp deep cycle leisure batteries.

 

[panelbeater]

i took an easy way.in back of t2 sits a 110amp leisure battery connected to a 1500/3000 peak inverter that if i need to i just run the caravan lead to caravan in and i have mains live in van.
now when i am driving i charge it from cigar socket through a 3 way,1 camera 1 battery,1 satnav/phone.socket.
when i turn over the socket is dead and only comes live when lump is running so no backwards draw.
only trouble i have found is when all connected and lump off the 3 way is live fed from back battery.not really a problem as camera/nav still on.
on restarting socket dies on turning over then livens up on running.
this works for me as in long dark nights out with van i have extra tv time when caravan battery gets low,i just connect to t2 and caravan charger kicks in when back t2 battery gets low inverter shuts down so i keep an eye on van voltage.
this set up works for me.and then going out in t2 charges back battery.

 

[Lazy-Ferret]

Some interesting ideas and thoughts about this subject.

How does the sensing circuit work taking a feed from the alternator light wire. Surely the light is only on when ignition is turned on and then goes out when the engine starts. No I know a relay can be open or closed circuit when enrgised or not, I get that that's no problem. But taking a feed that breaks the circuit when the light is on, but surely this will make the circuit when the light goes out. The light is also out when ignition turned off?

The lamp wire on an alternator is a bit weird... basically and very simply discribed, the lamp has a 12v ignition feed on one side, and the other side earths via the alternator warning lamp connector. Your relay is connected to the alternator side, and the other side of the relay is connected to ground.

So with ignition on or off, but the engine not running, the relay is effectivly earthed on both sides, so off...

Once the alternator is providing a charge, though, with the engine running, the voltage on the alternator warning lamp connector goes up to 12v, so this now means the dash bulb has 12v on both sides and goes out, but the relay now has 12v on one side, and ground on the other, so pulls in...

Hope that makes sense... by the way, the relay needs to be the sort that has a diode in it, and does matter which way round it is connected up.

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[Madmark]

I'm officially cross eyed now think ill stock to mechanics and upholstery. Electrical I wizardry to me I know simple basics but thats it lol

 

[Fez_uk]

If your going to do it do it properly and get something like a t-max split charge system.

Used this on my mav and defender worked great especially when one battery got killed by the cold.

http://www.jgs4x4.co.uk/t-max-split...stem-with-digital-battery-status-monitor.html

 

[Fez_uk]

Mel my darling, if you have 24v winch then you really need a separate 24 volt system ie two more 12v bats in series, and a 24 volt alternator, there is no way you can run this set up from 12v alternators, Rick

Yep many winch challenge competitors run 2 alternators, One 12v for vehicle electrics and one 24v alternator + batteries for winches.

You can get a box of electrics that give winch challenge competitors with 12v system the possibility to overvolt their 12v winches with 24v to increase speed but doubt this would work with a 24v winch constantly.

 

[kitchenman]

I fitted a second alt and meant to do a workshop, completely forgot, I will get onto it ASAP

 

[Terrano Steve]

Wanna do second battery as I'm running a fair few extras now and thinking second battery is needed. So what's best way to go about it I have nice gap passenger side now behind headlight just right for the second battery but what's the best way to wire it all up or do I just buy a kit off ebay nut seem pricey

If you are just looking for a bit of extra capacity I would just hitch up a second battery in parallel with the one you have.
Split charge circuits could be overkill for what you need unless you are doing say a lot of winching. Lots of the challenge guys around here still winching with one battery.

 

[Lazy-Ferret]

If your going to do it do it properly and get something like a t-max split charge system.

Used this on my mav and defender worked great especially when one battery got killed by the cold.

http://www.jgs4x4.co.uk/t-max-split...stem-with-digital-battery-status-monitor.html

That looks like a great option.. best of all worlds, and just needs fuses adding.

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[solarman216]

Hope that makes sense... by the way, the relay needs to be the sort that has a diode in it, and does matter which way round it is connected up.

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are you sure about that Clive, as the voltage through the bulb goes to the exciter in the alternator, if the diode is one way round it will block the voltage going to earth and so excitation will take place if it is the other way round surely it will sap the voltage to ground and no excitation will take place Rick

 

[Lazy-Ferret]

are you sure about that Clive, as the voltage through the bulb goes to the exciter in the alternator, if the diode is one way round it will block the voltage going to earth and so excitation will take place if it is the other way round surely it will sap the voltage to ground and no excitation will take place Rick

Hi Rick, the Diode is directly across the coil of the relay, so does not have any impact on the alternator circuit... it just acts to short the reverse EMF from the collapsing relay coil current back to ground, stopping it going up the wire and causing any potential upset to the Alternator components...

Personally, Since the electronics of the alternator can handle 70 odd amps, and the worst those small automotive relay coils could chuck out would be a lot less than that, I think it may be redundant and overkill, but a few people recommend it, and for the few pence extra it costs to get a relay with a built in diode, you might as well fit them just to be safe.

 

[solarman216]

Yes I understand where the diode is, and that is the point, the moment you fit a diode it becomes polarity conscious, connect it up the wrong way = diode no more, Rick

 

[Lazy-Ferret]

Yes I understand where the diode is, and that is the point, the moment you fit a diode it becomes polarity conscious, connect it up the wrong way = diode no more, Rick

Totally agreed... I made the mistake of connecting one the wrong way round a few weeks back for one of the Spot light circuits... breif puff of smoke, and a bit of a pong, and the Dioded relay became a normal relay...

I think you have misread my original post though Rick.... I did say it "Does" matter which way round it is connected up. I thought you were questioning if it needed to be a diode relay.