Thread: duel batteries

Originally Posted by clean32

ok this has got me all intrested

With the marine fitting, as I understand it.

When on both, is ok if both batteries have the same charge.
If the batteries have unequal charge, by putting it on both the batteries will want to Balance, IE the battery with the higher charge will discharge in to the lower charged battery, they will Balance. The down side of this is that the charging will happen at greater amperage than the lower battery can accept safely, IE you will stuff one or both batteries.

First off, there is actually no problem with connecting two batteries of different States of Charge ( SoC ).

Contrary to most people’s thinking, there will NOT be a massive rush of current from one battery to the other and although the batteries will “ EQUALISE “, it is not a case of the lower charged battery, being at 10.5 volts, and the higher charged battery, being at 12.5 volts, “ EQUALISE “ to 11.5 volts.

What will happen is that the higher charged battery will discharge down to the lower charged battery’s level.

In an extreme case, as above, with one battery at 10.5 and the other at 12.5, there will be a slight charging of the lower battery but in most cases, the extra charge in higher charged battery is simple wasted as it is drained by the lower charged battery.

The “ EQUALISE “ will not occur instantly with a massive current rush but will take hours to days before both batteries are at the same SoC.

Originally Posted by clean32

What we do is drive around on one battery to charge, when charged change to the other battery. All systems and the car run on the one battery, until I change it over then we run on the other.

Even with a small alternator, you are far better off charging both batteries at the same time otherwise it is going to take up to twice as much driving time to get both batteries charged.

Originally Posted by clean32

These automatic systems I am uncomfortable with because. Even if the main battery is isolated from the ancillary systems, what happens if the main battery decides to die in the middle of nowhere? Charging the second battery is charged though another control box, these ( when I was looking into it) are quite slow chargers. at the moment we can top up a charge in a few hours driving but with some of these charging systems you would need to drive a bit longer.

Don’t know where you got that info from but most Solenoid ( relay ) based isolators charge both batteries at the same time and the speed with which the batteries charge is only limited by the current output of your alternator.

Originally Posted by clean32

The cheaper normal ( quality) car battery) are only % less in capacity IE I have 2 120AH batteries I think its a bit to complicated and risky just for the benefits of 120 + 160 AH batteries for example.

Not sure what you are saying there?

Originally Posted by mcrover

Well, with mt Pirahna system, if I kill the start battery, it is just a matter of joining the 2 terminals on the unit and the batteries and wiring are joined and you just disconnect the negative off the start battery.

All you need to do is connect the positive of one battery to the positive of the other battery, using one battery jumper lead.

If the dual battery set up is wired correctly, there should be no need to connect the negatives, as they should be earthed properly in the first place.

Originally Posted by mcrover

The problem with the manual systems is they WILL kill your batteries because unless both batteries are the same size and the same age (a matching set) then 1 battery will always draw off the other.

Sorry mate, but this is nothing more than fiction.

Originally Posted by mcrover

The other problem is that you can forget to switch it on to connect the batteries together while driving and then your fridge will run out of cold due to lack of electricity.

I agree with this and it’s why such set ups are commonly referred to as Idiot Switches.

Originally Posted by mcrover

The auto systems are pretty reliable and not worth fearing as with these new fangled deep cycle thingies that will make a fridge run for days instead of just a few hours........

And if you had fitted one of my controllers you would be able to operate your fridge for around 50% longer between chargers, than you can with any other controller.

Originally Posted by drivesafe

Quote:
Originally Posted by mcrover
Well, with mt Pirahna system, if I kill the start battery, it is just a matter of joining the 2 terminals on the unit and the batteries and wiring are joined and you just disconnect the negative off the start battery.

All you need to do is connect the positive of one battery to the positive of the other battery, using one battery jumper lead.

If the dual battery set up is wired correctly, there should be no need to connect the negatives, as they should be earthed properly in the first place.

On my Pirahna system it has 2 x 1/4" Unc studs coming out which the main and aux batteries go onto.

I have in the past when the main Bat crapped itself, just undid the nuts and piggy backed the aux and main lines on the 1 post on the unit.

I then disconnected the negative lead off the main battery to remove it from the system so it didnt draw down the second battery (Which was a 120Ah deep cycle which cranked it over no worries for a couple of weeks) as the alternator goes to the main battery first and that then feeds the Pirahna system it was easier to leave the pos all connected to the main


Quote:
Originally Posted by mcrover
The problem with the manual systems is they WILL kill your batteries because unless both batteries are the same size and the same age (a matching set) then 1 battery will always draw off the other.

Sorry mate, but this is nothing more than fiction.

Ok Tim im talking from experience with electric vehicals and 24v truck set ups so it may be a bit different with these sort of automotive set ups but you could explain why that it Tim




Quote:
Originally Posted by mcrover
The other problem is that you can forget to switch it on to connect the batteries together while driving and then your fridge will run out of cold due to lack of electricity.

I agree with this and it’s why such set ups are commonly referred to as Idiot Switches.




Quote:
Originally Posted by mcrover
The auto systems are pretty reliable and not worth fearing as with these new fangled deep cycle thingies that will make a fridge run for days instead of just a few hours........

And if you had fitted one of my controllers you would be able to operate your fridge for around 50% longer between chargers, than you can with any other controller.

If the Pirahna system wasnt in the Disco when I bought it then I would have one of yours now but.....If it aint broke, dont fix it