Duel 12v batteries + another into a camper trailer/ triple..

[mud4b]

ok i have searched triple batteries but only came up with 1 post that was almost relevant (it was 2 batts = 24v and 1 12v batt).

i have duel batteries in my jimny controlled by a redarc controller. first one is for the starting system, hid lights, ect (main battery), 2nd is a bluetop orbital for the stereo and the fridge. i want to run a 3rd in the camper trailer using anderson plugs to connect it to the 2nd battery (bluetop orbital) so it gains some charge when hooked to the vehicle.

my question is how do i do this, do i need another redarc controller between battery 2 and battery 3 or can i just run it straight through (fused) to the 3rd battery.

also will the alt handle the charging to a point (its only a 80 amp.

cheers mark

[98lux]

I just got one of these from Traxide (drivesafe from the forum)
http://www.aulro.com/afvb/verandah/5903 ... -kits.html



The only difference with the pics in the link is, if you want a "true" triple battery system the blue wire goes the the 2nd battery and the grey wire goes to the camper that way they are all seperate from 1 another, or you do as the pics and the 2 aux batterys are linked.
SC80 controler on the below site.

http://www.traxide.com.au/

[mud4b]

cheers for that, not sure its what im after though as i do not want to replace the controller for my currant duel battery setup as i trust the redarc and its brand new.. i really wanted a add on solution.

cheers mark

[chimpboy]

It depends on how exactly you want it to work.

If you are happy for B3 to drain B2 to charge up (but still protect B1), then you can just put it in behind your existing controller.

If you want to protect B1 from B2, and B2 from B3, then you need another controller.

Based on what you're saying you're using it for, it sounds like it would work for you to just have the third battery charging from the existing controller. Ideally since B2 and B3 would then be in parallel, it would be good to have identical batteries but it's not really essential imho.

I would wait to hear what Drivesafe and others say though.

[fazza81]

Thats it Chimpboy

I have mine hooked up B1 redarc B2 direct to B3 in the camper.

works like a treat and if i need more power in the camper I just hook it up to the car via an extension lead I made up.

[midi73]

Just buy one of these.
http://www.sidewinder.com.au/page82.html

[drivesafe]

Hi mud4b, following on from 98lux's post, use the diagram below and just substitute your Redarc for the SC80.

Everything else will be the same.

NOTE, the black cable can be connected to either the cranking battery ( as shown ) or the auxiliary battery.

Cheers

[+dj_hansen+]

drivesafe... does the third battery need to be identical to the secondary battery in construction....

For instance could i run a wet cell deep cycle secondary, and an AGM Orbital as a third battery?

[drivesafe]

Hi Dan, it makes no difference what size or type any of the batteries are, all will fully charge and all will discharge at the same voltage levels.

There are lots of myths around, about the theoretical problems that will occur if you fit different types of batteries in a dual battery set up. I’ve supplied many thousands of dual battery controllers and have NEVER had any feed back of any form of problems occurring when using different types of batteries.

Cheers

[fester2au]

I had the dual redarcs set up just as you were first thinking Mark in my Patrol and now the cruiser. My thinking was that I was unlikely to really need heaps of charge in both aux batteries at the same time as we have plently of reserve in the van and the second in the truck is mostly for just getting the Engel to where we are going of for day tripping. At best for an overnight stop. If we are camped for a coouple of days then the Engel comes out and gets powered by the van batteries. If we only go overnight the Engel normally gets left in the truck or it gets thrown back in if we are going exploring for a few hours and want drinks of lunck along the way. Not sure if perfect set up but has never let us down.

[chimpboy]

Hi Dan, it makes no difference what size or type any of the batteries are, all will fully charge and all will discharge at the same voltage levels.

There are lots of myths around, about the theoretical problems that will occur if you fit different types of batteries in a dual battery set up. I’ve supplied many thousands of dual battery controllers and have NEVER had any feed back of any form of problems occurring when using different types of batteries.

Cheers

Just my opinion, but I think it might matter very slightly. You might sit on less than the full possible charge with one of the batteries. But it won't be much and it wouldn't lead to any practical issues.

Where it really matters is if you have a 24V setup. In this situation one weaker battery can kill the other one.

[-Scott-]

Just my opinion, but I think it might matter very slightly. You might sit on less than the full possible charge with one of the batteries. But it won't be much and it wouldn't lead to any practical issues.

Guessing that you've based this opinion on more than "gut feel", what do you believe will stop one battery from reaching full charge?

[chimpboy]

Just my opinion, but I think it might matter very slightly. You might sit on less than the full possible charge with one of the batteries. But it won't be much and it wouldn't lead to any practical issues.

Guessing that you've based this opinion on more than "gut feel", what do you believe will stop one battery from reaching full charge?

to be honest, not much more than gut feel. Only that if the batteries aren't identical and they are connected in parallel, then there would have to be some current flow between the two of them when they aren't being charged, however small. And if that were the case then the stronger battery would have to wind up at something less than the full charge it would have had if the two batteries had been disconnected.

For example let's say the two batteries were VERY different, not just ever so slightly different. eg one was pretty well stuffed and the other wasn't. I am pretty sure that leaving them hooked together would cause the good one to discharge faster. That's an extreme difference but I imagine a slight effect along the same lines from a slight difference.

But don't get me wrong, I am not suggesting that this actually matters in the real world. And, I could absolutely be wrong... I only said it "might" matter a little bit!

[-Scott-]

if the batteries aren't identical and they are connected in parallel, then there would have to be some current flow between the two of them when they aren't being charged, however small.

For this to happen, the "weaker" battery would need to accept a current opposite to discharge current.

Presuming the "stronger" battery is at 12.6V (nominal terminal voltage for a fully charged 12V lead acid battery) how much charge current will another healthy 12V battery accept at this terminal voltage? Can a "discharging" electro-chemical reaction in one battery produce enough voltage to reverse exactly the same reaction in another battery? Not when I studied chemistry.

So, as I see it, the only way for the "weaker" battery to accept a current from the "stronger" battery would be if such a current can flow without actually charging the weaker battery.

I'll try an analogy. Consider two cylinders the same height, full of water, connected at the bottom. The water level in both cylinders will be identical, yes?

But what if one cylinder has a larger diameter than the other, so it holds more water? Will the levels remain the same? Can water flow from the larger cylinder without increasing the level in the smaller cylinder?

Is this a valid analogy?

[drivesafe]

Hi folks, having discussions on using dissimilar batteries is always has this “gut feel” to it but consider these three scenarios and see if you can find a difference.

Scenario 1. You have a dual battery set where you have two batteries of different types ( for argument sake 1 AGM and 1 Flooded Wet Cell [ FWC ] ) and through use the AGM has a higher charge than the FWC when they are connected together. In this scenario what will happen.

Scenario 2. You have a dual battery set where you have two batteries of different types ( again for argument sake 1 AGM and 1 FWC ) and through use the FWC has a higher charge than the FWC when they are connected together. In this scenario what will happen.

Scenario 3. You have a dual battery set where you have two identical batteries ( no matter what type ) and through use one has a higher charge than the other when they are connected together. In this scenario what will happen.

Do the math and you will come up with the same answer for all three scenarios.

Next, you have two dissimilar batteries ( once again for argument sake 1 AGM and 1 FWC ) permanently connected in parallel and so the are both charged and discharged together.

During charging the AGM is likely to charge quick than the FWC but eventually, if give enough time, both batteries will be full charged.

With both batteries fully charged, once the charging source is removed the batteries will have a surface charge that is higher than either batteries state of charge.

Under normal circumstances, fully charged AGM batteries can have a slightly higher voltage than fully charged FWC batteries, but the difference is only about 0.1 of a volt

If you apply a load, say connect a fridge, the fridge will very quickly use up this surface charge and will then draw the bulk of it’s load from the highest charged battery at first but will progressively spread it’s load over both batteries at their voltage become the same. In this case no stored power is lost.

If on the other hand, you remove the charging source and just leave the batteries in a No Charge - No Load state, the AGM will progressively discharge down to the FWC’s voltage level.

This levelling of voltages won’t happen instantly but depending on just how much of a difference there is, will take a few ours to a few days the occur.

In this situation, you will have wasted at worst, about 5% of the stored capacity of the AGM. So if you had two 100 A/H batteries connect, 1 x AGM and 1 x FWC, that were capable of running a fridge for say 80 hours, if you had two AGMs, you could have run the fridge for nearly 82 hours and so the difference is just not worth considering.

In reality, just the age of any battery can have a far greater effect on how long it could run the same fridge for.


There is heaps more to it but this is just a crude idea of what happens

[chimpboy]

So, as I see it, the only way for the "weaker" battery to accept a current from the "stronger" battery would be if such a current can flow without actually charging the weaker battery.

Yes, this is what I think would have to be happening. For example the weaker battery could be trivially warmed up by acting as a conductor for a tiny bit of current.

Put it another way, when the two batteries no longer have a charge coming in from the alternator, they are going to somehow equalise/stabilise. The stronger battery can go down, but the weaker battery can't go up.

But to reiterate, I completely agree the problem, if there is one, is going to be next to nil. And I'd absolutely cave in to an expert on the topic at any time, it's just idle thinking. I would happily use different batteries if they were both in good nick.