Second Battery fitment hardware

[Terranosaurus]

A few years back I gathered up the bits to make up kits for second battery installs but never got round to actually selling any.

Would anyone be interested in these if I gather the stuff up out of the garage and make them up into kits?

Will include the steel battery tray and all the bolts needed to fit one on the opposite side of the engine bay. The clamp itself you can source from a factor or a breakers as they are all the same.

No electrical hardware with these though.

Pics of mine in place which have been there a few years now and held up to serious offroading etc

Just looking to get back some of the money I put into these so won't be expensive and postage at cost. Should be sub £20 all in but will need to check postage etc

 

[(RIP) PLANK]

I don't have space for a second battery, but out of interest, what exactly will be in the kit? :thumb2

 

[Terranosaurus]

As above

Will include the steel battery tray and all the bolts (stainless) needed to fit one on the opposite side of the engine bay. The clamp itself you can source from a factor or a breakers as they are all the same.

No electrical hardware with these though.

 

[(RIP) PLANK]

As above

ok, so it's basically a battery tray then :thumbs

 

[Lincs Mav]

I could possibly intrested in x2 Simon. but not until october have a wedding to pay for at the min.

Cheers Gav

 

[rustic]

I made my own tray, and I used threaded bar, and a plate across the top of the battery, rather than a base clamp.

Just a point, I see you have connected both batteries in parallel, this is fine if both batteries are the same type, age etc, but if one of the batteries is older, it can drain the other. Also if you leave the interior light or other device on, you will discharge both batteries
Incidentally if a cell went in one battery, you will discharge the other one too.

So if you want the battery as a back up in case the other one dies, then I suggest you have a solenoid linking both positives, with a switch to pull in the solenoid, should you need the extra boost.
For the Solenoid, I fitted a starter solenoid from a 1970's vehicle, it was actually new, so cheap and easy to fit and they can carry 500 amps for starting if required.
I also wired in a heavy duty relay that connects both batteries using the " radio supply for 12 volts, to activate the coil on the relay, so the second battery is charged when the engine is running ( split charge relay) BUT does not connect when the engine is starting.
When the engine is off and the key removed, the second battery is totally isolated.

It is impractical to use the starter solenoid as the isolator ( ie to energise it to charge the second battery) as they are not continuously rated, but if only used for a few seconds whilst cranking they are fine.

So before wiring up the second battery consider what you want to use it for.
The battery interconnection cables needs to be a minimum of 25mm2 if you are using it as a back up start. This cable is good for 170 amps, continuous, but for a few seconds can carry more, but with an acceptable voltage drop.

Hope this helps.
PS check with your insurance company before fitting, that this is an acceptable mod, I have convinced my insurance company.:thumb2
Some will not allow it.

Rustic

 

[solarman216]

Good post Rustic, spot on, Rick

 

[Terranosaurus]

Just a point, I see you have connected both batteries in parallel, this is fine if both batteries are the same type, age etc, but if one of the batteries is older, it can drain the other. Also if you leave the interior light or other device on, you will discharge both batteries
Incidentally if a cell went in one battery, you will discharge the other one too.

If you look you can also see the split charge relay. Both batteries are of the same type and age, but I'm sorry like many things on the internet the battery discharge from one to another is just an urban legend - provided both batteries are holding the same voltage, which if charging from the same alternator they will be unless left a long time then no current will flow for one battery to discharge into the other. For one battery to overcome the potential of the other the difference would have to be substantial which unless you have a totally knackered battery it just won't be. All that will happen is the higher voltage battery will trickle away a tiny bit of charge until the potential in the two batteries became equal then all current flow will cease. Say one is sat at 12.7v and the other at 12.8v then the later will put 0.1v across the other which has to discharge through the internal resistance of the battery (ie very slowly) any charge loss is so negligible to be considered as none.

Oh and that is 70mm2 cable more than up to the job, but you can't quote current spec for any given cable on cross section alone you need number of strands and their size too and you also need to consider the insulation thickness as that has a bearing on cooling. These factors are why modern thin wall wire as used by manufacturers (and loom builders such as myself) has a higher current rating than the traditional wire you will buy or as was fitted to older cars.

 

[solarman216]

If you look you can also see the split charge relay. Both batteries are of the same type and age, but I'm sorry like many things on the internet the battery discharge from one to another is just an urban legend - provided both batteries are holding the same voltage, which if charging from the same alternator they will be unless left a long time then no current will flow for one battery to discharge into the other. For one battery to overcome the potential of the other the difference would have to be substantial which unless you have a totally knackered battery it just won't be. All that will happen is the higher voltage battery will trickle away a tiny bit of charge until the potential in the two batteries became equal then all current flow will cease. Say one is sat at 12.7v and the other at 12.8v then the later will put 0.1v across the other which has to discharge through the internal resistance of the battery (ie very slowly) any charge loss is so negligible to be considered as none.

OH sorry but total rubbish, this all assumes no faults, but any battery can fail at any time, and when it does, as in my case some time ago it results in a near explosion situation, ie 12 other batteries in parallel feeding one that had shorted, now have 2 volt cells in series = no problem, Rick

 

[(RIP) PLANK]

To be fair my knowledge of Electrics and Electronics is pretty 'old school' now, but both explanations make sense, for current to flow there has to be a potential difference. But in the event of a battery failing I see that it could, at the very least, scrap the second battery. Plus if you had a current leak draining your battery, it may take longer to go flat but you would still end up with no back up power in an emergency if you run them together :nenau