Yup they most definitely will balance between both batteries.....you need another isolator inline between second and third battery.....gets expensive.....I have exactly this setup without the isolator which does work but I find it never charges both batteries to full no matter how long Im on the road for with no draw coming off 2nd or 3rd battery....also have two different sized batteries ...100ah and 200ah in camper so this also doesnt help.....will be installing another redarc isolator in camper with solar charge input as well...also thinking of a third incar battery .....the expense is doing my head in but will be worth it in the long run I guess..

 

I didn't realise you can run another soleniod.

Maybe I should do that too and run a freezer in the camper.

Would you run the 2nd soleniod in the camper or car?

 

I'm no expert but if you put a solenoid between the batteries when you turn the car off the batteries will be isolated from each other so the solenoid would need a link switch on it so you can use both batteries together again. I would also expect you would need to use the same type of battery cables or something close to that size between the 2nd & 3rd batteries so it will get charged correctly twin core 6mm would not be enough it might work for a short time then once the battery is down on power you will start to have problems. Also does your alternator have enough output for all of your requirements

 

Will certainly beef up the wiring between batteries.

Will be running 3 lead acid batteries and i run next to no accessories aside from the radio or UHF and fridge off the aux, I think the standard alt should be enough?

 

Hi Paddy and first off, there is absolutely no advantage gained by installing another isolator between your second and third battery.

You can safely connect any number of batteries in parallel, even if one is at a higher state of charge than the other, when you connect them.

All that will happen is that, as you questioned, the batteries will equalise and this has no harmful effects on either battery.

In a case where the batteries are at an extreme difference of charge, there will be some loss of energy while the batteries start to equalise but it will take as much as 24 hours for these batteries to settle to the same charge level.

Furthermore, it does not matter if the batteries are the same type and size, or if they totally different sizes and types, the reaction is the same and again, there will be no harm caused to any battery in the setup.

The one point made above, is to make sure you are using heavy enough cabling. 6B&S ( 13.5mm2 ) cable is idea and you need to run both positive and negative 6B&S cabling.

 

Cheers for the info drivesafe, makes it a cheap exercise

 

Putting an isolator between your second and third battery won't charge it any more. The isolator turns on at 13.4V (my numbers may be a little out here) so when the battery reaches this it'll turn on and join the battery. With two isolators and 3 batteries, you're essentially creating 1 huge battery once they all equalise.
Perhaps look at a BCDC system instead? It'll charge the battery to a true 100% and help keep the battery in good condition longer. You also don't suffer from voltage drop like you do with isolators over long distances. It's a bit more, but it is a more reliable system. Worth looking at anyway.

 

Perhaps look at a BCDC system instead? It'll charge the battery to a true 100%.

And as Paddy's alternator operates at the same voltage as the DC/DC device, it will achieve the same results.

You also don't suffer from voltage drop like you do with isolators over long distances. It's a bit more, but it is a more reliable system. Worth looking at anyway.

Hi Rhys90 and I can only imagine where you get this sort of info from.

If you have a low battery and you run decent cabling between the alternator and the auxiliary battery, like as posted above, 6B&S cable, then if you have a low battery at the start of your drive, you will actually have a lower charge voltage at the battery if you use a DC/DC device than if you charge straight from your alternator.

The only time a DC/DC device will charge at a higher voltage is if the cabling is so thin that the load causes a large voltage drop and here again, it would still be far cheaper and more efficient to fit decent cabling rather than fit a DC/DC device.

Being as Paddy’s alternator runs at the same voltage that a DC/DC device can get up to, and the DC/DC device’s 14.4v is only at the end of the charge cycle, so again, Paddy is far better off using his alternator, because he will charge low auxiliary batteries much faster.

 

I've got duel batterys in the Troll, connected by a Red Arc solonoid. I've then got 6B&S running to an anderson on the back, conecting to my camper (more 6B&S) to 2 Deep Cycles. I havnt had any problems with this setup.

I've even gone so far as making up a "6B&S extention cord" so when the camper is setup and the car is 'near by' I connect them both up and effectively have 3 batteries in the camper

 

Brilliant! I thought I was the only one to have made an "extension cord" like this, I only have one battery in my camper unlike Fireguard's two but same principle; if car is close to trailer but I don't want it so close that it's a pain in the bum to get into the back of it I use the extension, so overnight the fridge has the advantage of both batteries (less discharge for each = better long term health) and in the daytime the solar charges both.

 

Where did you wire the solar input into your configuration fireguard?

 

The panel itself is self contained (I.e. has the regulator attached) and at this stage is only and 80W foldup set because I also use it without the camper (swagging on the beach fishing with the fridge in the car for the weekend etc), But what I did do is loped the alligator clips off the end of the cord and put an Anderson plug on there. I've got a spare Anderson plug on the trailer wired directly to the batteries, all I have to do is plug it in. Did a simular thing to the car - put a spare Anderson underneath/inside the bulbar connected to the second battery.

Can connect the camper or solar to the front or rear of the car, and have two plugs on the front of the camper

 

Ripper, cheers for the info!

 

also, after I cut off the alligators I also put an Anderson on those too, got the best of both then, Anderson to Anderson on my gear, but if the panel gets borrowed and they don't have an Anderson setup all I have to do is plug the alligators back on and clip them to the battery as normal

 

Hi Leethal and I think you also misunderstand how DC/DC devices work.

You can read all the info ( advertising hype ) about these devices but this “info” does not completely explain how these devices work.

Most people see the specs for these devices, where is states they will charge at say 14.4v, and think this is the voltage they always charge at.

This is only partially correct.

They will only charge at 14.4v once the battery gets to around the 80% SoC mark, and then these devices operate at 14.4v.

With batteries at lower states of charge, these devices operate at LOWER voltages than your alternator. And they operate at lower voltages because they are current limited, something your alternator is not.

Using a similar example to yours, I was experimenting with some new isolators and discharged an Optima D34 Yellowtop 55Ah deep cycle battery down to 11.58v, or 20% SoC, which is a safe level of discharge for any new deep cycle battery.

I had a 6m length of 10mm2 twin ( 12 return length ) and when I started the motor, the voltage at the cranking battery ( which was also at 11.58v ) quickly rose to around 14.16v but the voltage at the Optima was just 13.32.

BUT, the optima was still drawing 61 amps at that voltage.

If I had installed a 20 amp DC/DC device right beside the Optima, the voltage at the Optimas terminals would have been around 12.5v, at best.

By the way, the Optima reached better than 90% SoC in under 90 minutes of driving.

It would have taken a 20 amp DC/DC device about 2.5 hours to reach the same level and this is with a small 55Ah battery.

If it had been a 75 amp Optima, the alternator would still have charged it to around 90% SoC in a little over 90 minutes but the 20 amp DC/DC device would now need around 3.5 hours to do the same.

The devices work, but no where near as well as the advertising hype would have you believe.

 

Fair enough.

As much as I am loath to stray off topic, I have another question. How accurate/reliable are Hall effect sensors for measuring amps? The reason I ask, let's say all three of my batteries (car main plus aux, camper) were for all intents and purposes fully charged, and my alt put out ten amps to cover fridge, fuel pump, and a couple of minor things.

It then stands to reason that if I've camped for a night or more, when I drive off again, the alt's output will gradually drop (amps) as the two aux batts approach their higher soc, so I could use this to give myself a rough idea of when they are pretty close to happily charged. Not too accurate but good for a rough idea, if these type of gauges are pretty accurate and reliable, unless there is a better suggestion?

 

Hi Leethal, hall effect devices can be very accurate and have the advantage, in the tong or clamp version, of not needing to insert them into the actual wiring.

But using shunts, which means you would have to insert them into the wiring, but are easier to monitor and cheaper to set up.

Shunts are commonplace and the way of using them is straightforward, using something as simple as a digital multi meter, but shunts are designed to monitor the negative cabling.

An advantage of using hall effect devices is that they can be used to monitor either the negative or positive cabling, which can make it lot easier to monitor a specific circuit.

Also, if you set up the hall effects as a permanent monitoring device, monitoring the positive circuits, because they would be what is known as a high side monitor, you could set them up to work as over current warning and trip devices if you needed this sort of protection.

This is something that a shunt are not good for because in many circuit setups, a shunt can not “see” a dead short, whereas high side monitoring can see dead shorts.

 

Thanks for that. Another question, if I may, can Hall effect sensors 'see' the current direction? To illustrate my question, if I had one on say the positive feed from the second battery heading off toward the rear of the car, and it showed say 3 amps current flow, now that could be 3 amps coming in from the solar panel, or 3 amps going out to the fridge, so does it show a current direction so I can determine if the battery at that instant, is charging or discharging?

 

While we're on the solar panel subject, anyone had experience with these? Looks a little more robust that most I've seen and we tend to travel in some pretty rough areas.

Folding Solar Panel 100W Impact Water Resistant Portable KIT | eBay