Charging setup for 2 leisure batteries (2 Viewers)

[gazza280]

Hi Guys

This might seem like a newbie question but I need an answer.
I have just bought 2 new 110amh batteries to put in the van to give me 220amh. I am replacing an old 110amh battery that came with the van.
I am a complete novice with electrics but if I were to just replace the battery like for like there would be no problem because the setup is the same, but because I am adding another leisure battery, I am confused to how they charge.
Normally on hookup I have the battery charger charging the batteries "starter and leisure" and when driving the van the alternator is charging the starter first then the leisure battery.

Now I want to add another battery to the mix, so does the battery charger that I am using now still charge both batteries, independently, together or does only 1 of the leisure batteries get charged.

Do I need a new charger to replace the one I already have do I need to put a split charger between the 2 leisure batteries?
I have looked at possible solutions but there are so many I am totally confused. Aggghhh!

Isolator switch, split relay, intelligent charger ie: ctek, sterling battery 2 battery charger?

I like the idea of having an intelligent charger like the ctek because it checks the batteries at different stages to get the best from the batteries.

Looking on google and youtube, the videos of people who have added extra batteries just hook the batteries together, in parallel of course, with not a charger or split charger in site.
Now I know that if I'm going to get a definitive answer its gonna come from one of you guys, so much appreciation in advance, and remember I know very little about electrics.

Many thanks
Gary:thumb:

 

[tonyidle]

If the two are close together (in the same compartment) simply do as you suggest & connect them together + to + and - to -. Use the same size cable as is used at present. If they are separated by being in different locations do the same but include a fuse at each end of the cable linking the +ve terminals. Use 50A fuses. Any charging arrangements will charge both batteries as if they were one. A smart charger is a very good idea if the existing charger fitted to the 'van isn't already a smart charger.

 

[Dolomite Pete]

Assuming the two batteries are close together and connected in parallel (put a 10amp fuse in positive wire connecting the two batteries), you should then arrange the power take off from the neg of one battery and the pos of the other. This minimises the losses due to internal resistance. I've done the same thing on my van recently. All of the original charging systems (driving and hook up) all work fine with out doing anything else.

^{_{Subscribers  do not see these advertisements}}

 

[beachcaster]

A solar panel will keep both batteries topped up.......and I also have one of those smart boxes that auto switches between topping up the vehicle battery and the leisure batteries.

barry

 

[Steve304]

Assuming the two batteries are close together and connected in parallel (put a 10amp fuse in positive wire connecting the two batteries), you should then arrange the power take off from the neg of one battery and the pos of the other. This minimises the losses due to internal resistance. I've done the same thing on my van recently. All of the original charging systems (driving and hook up) all work fine with out doing anything else.

Now I'm confused as well!

Like the OP, this is something that I have considered doing as well but there is conflicting information from the two posts answering the question already.

Are the batteries connected + to + and - to -, or as Dolomite Pete states above - to + and + to - ? Also, if they are located side by side in the leisure battery cabinet. Do they need a fuse?

Please clarify if possible and thanks for your help.

Steve

 

[gozomike]

For 2 12volt batteries always + to + and - to - anything else would result in a big bang. I am sorry I did understand what Dolomite Pete said and it is not what you suggest. If you do not fully understand it is best to get someone who does to do the connections.

^{_{Subscribers  do not see these advertisements}}

 

[phase3begins]

More than you will ever want to know.....

http://www.smartgauge.co.uk/batt_con.html

Paul

 

[TheCaller]

I really must take the time to learn how to use a sketching program - a diagram would really help here.

Let's assume that you have room to put the new battery right next to the replacement one. It's certainly better if you can keep them together.

Let's call the replacement battery A & the 2nd new one battery B.

Disconnect the negative terminal from your old battery first. Then disconnect the positive terminal, remove the old battery & put the new one (A) in position. Put battery B next to it.

Now connect the positive terminals of both new batteries together, using wire of similar thickness to the existing leads. Then connect the negative terminals together. In effect, you have now created one big 12v battery.

Now reconnect the positive lead to battery A, just as it was connected to the old battery.

Finally, reconnect the negative lead, but if possible, don't connect it to battery A, connect it to battery B. This is the point Dolomite Pete was making. This ensures the load is equalised between the two batteries. If you connect both leads to battery A, it will always have to carry more of the load, because even a small voltage drop in the connecting wires will cause battery A to do more work. If you can't easily connect your negative lead to battery B, then use the biggest wires possible to connect the two batteries together, to minimise the voltage drop.

When you consider that the voltage difference between a fully charged battery & a flat one is less than 2 volts, even when under load, then even a tiny voltage drop makes a big difference.

Fuses

Many people consider a fuse unnecessary if the batteries are next to each other. The further apart they are, the bigger the connecting cables should be (voltage drop again) & the greater the need for a fuse to protect the cable. A 10A fuse in the positive lead should be ok for normal 12v loads, but if you have an inverter, or anything else that could put a high load on the batteries, I would up that to maybe 40A.

 

[TheCaller]

More than you will ever want to know.....

http://www.smartgauge.co.uk/batt_con.html

Paul

Very true; that site is the absolute bible if you want to know how it should be done.

Most of it is overkill for a two battery motorhome setup, but for emergency vehicles and marine applications, it's the place to be. Anyone with 3 or more batteries needs to read that site, even if they don't put it all into practice.

^{_{Subscribers  do not see these advertisements}}

 

[Daedalus]

Simple diagram of battery connections for a twin battery setup attached....

Daedalus

 

[TheBig1]

battery load balancing and internal resistance is good in theory but unnecessary in practice with a 2 battery setup, especially if they are side by side

keep it simple so you dont add potential failure points

 

[pappajohn]

as previously said by others.......a fuse at both ends of the pos wire.....the attachment explains why.

fuse size is to be considered as well.

if you use 20amp rated wire to link the two batteries you dont want 50amp fuses....in a fault situation the wires will melt before the fuse blows as the current carrying capacity of the wire is far lower than that of the fuse/s .

^{_{Subscribers  do not see these advertisements}}

 

[VXman]

I really must take the time to learn how to use a sketching program - a diagram would really help here.

Let's assume that you have room to put the new battery right next to the replacement one. It's certainly better if you can keep them together.

Let's call the replacement battery A & the 2nd new one battery B.

Disconnect the negative terminal from your old battery first. Then disconnect the positive terminal, remove the old battery & put the new one (A) in position. Put battery B next to it.

Now connect the positive terminals of both new batteries together, using wire of similar thickness to the existing leads. Then connect the negative terminals together. In effect, you have now created one big 12v battery.

Now reconnect the positive lead to battery A, just as it was connected to the old battery.

Finally, reconnect the negative lead, but if possible, don't connect it to battery A, connect it to battery B. This is the point Dolomite Pete was making. This ensures the load is equalised between the two batteries. If you connect both leads to battery A, it will always have to carry more of the load, because even a small voltage drop in the connecting wires will cause battery A to do more work. If you can't easily connect your negative lead to battery B, then use the biggest wires possible to connect the two batteries together, to minimise the voltage drop.

When you consider that the voltage difference between a fully charged battery & a flat one is less than 2 volts, even when under load, then even a tiny voltage drop makes a big difference.

Fuses

Many people consider a fuse unnecessary if the batteries are next to each other. The further apart they are, the bigger the connecting cables should be (voltage drop again) & the greater the need for a fuse to protect the cable. A 10A fuse in the positive lead should be ok for normal 12v loads, but if you have an inverter, or anything else that could put a high load on the batteries, I would up that to maybe 40A.

Bit of an old thread resurrection but can someone tell me. The advice above is not the same as this image below? Am I right in thinking that. and if so, which is correct?

For info - the image is from here: https://caravanchronicles.com/guides/how-to-connect-two-batteries-in-parallel/

 

[Bolti]

Bit of an old thread resurrection but can someone tell me. The advice above is not the same as this image below? Am I right in thinking that. and if so, which is correct?

View attachment 511023

For info - the image is from here: https://caravanchronicles.com/guides/how-to-connect-two-batteries-in-parallel/

The advice above is as your diagram
Positive and negative feeds on opposing batteries.

 

[TheCaller]

As I implied at the time, a picture is worth a thousand words!

The picture is correct & is what I was trying to say. On re-reading my post seven years later, I would revise my fuse sizes upwards, by a factor of at least 2, more for a substantial inverter, although that would raise a whole series of other questions.

^{_{Subscribers  do not see these advertisements}}

 

[Andacami]

Even though an old thread, on some control panels you can alter the AH for the leisure batts to match your new total AH. I believe all this does is help with the display accuracy although it "might" impact the smart charging too.

I've just gone from single 95AH to two 100AH in my AS Corinioum, wired as described, I also reset my EC480 to account for 200AH rather than 95AH AND I set it at 100% charge as I know they were fully charged when fitted.

 

[VXman]

Even though an old thread, on some control panels you can alter the AH for the leisure batts to match your new total AH. I believe all this does is help with the display accuracy although it "might" impact the smart charging too.

I've just gone from single 95AH to two 100AH in my AS Corinioum, wired as described, I also reset my EC480 to account for 200AH rather than 95AH AND I set it at 100% charge as I know they were fully charged when fitted.

Interesting - I hadn't thought about this aspect. I'm going from one 95ah to two 95ah's. The charging etc is managed through a electroblock ebl 119. Is there anything I need to do to this and will the voltage display correctly on my Burtsner Guage?

Also, I'm looking at battery cable for linking the batteries which will be next to each other. Does anyone know mm size the standard battery cable is?

 

[TheBig1]

Also, I'm looking at battery cable for linking the batteries which will be next to each other. Does anyone know mm size the standard battery cable is?

The size will depend on the maximum load and the distance apart, although in this case together. Always over specify the size of cable you choose, with a minimum of 35mm csd

^{_{Subscribers  do not see these advertisements}}

 

[autorouter]

Does anyone know mm size the standard battery cable is?

Cables are usually described by the cross-sectional area (CSA) of the copper core, measured in square millimetres, and abbreviated to mm2 on here because a proper 'superscript 2' is not available.

Some suppliers measure the cable diameter, including the insulation layer, in millimetres. There are tables showing the diameter in mm with the CSA in mm2. For example a 16mm2 CSA cable is 7.3mm diameter. Occasionally the '2' is dropped, so that 16mm2 is written as 16mm, which adds to the confusion.

Cable size table | 12 Volt Planet

A guide on cable sizes from 12 Volt Planet

www.12voltplanet.co.uk

If you want to know the size of the existing cable, it is often stamped on the outside at regular intervals. A torch shining at a shallow angle will make it easier to see.

 

[VXman]

Cables are usually described by the cross-sectional area (CSA) of the copper core, measured in square millimetres, and abbreviated to mm2 on here because a proper 'superscript 2' is not available.

Some suppliers measure the cable diameter, including the insulation layer, in millimetres. There are tables showing the diameter in mm with the CSA in mm2. For example a 16mm2 CSA cable is 7.3mm diameter. Occasionally the '2' is dropped, so that 16mm2 is written as 16mm, which adds to the confusion.

Cable size table | 12 Volt Planet

A guide on cable sizes from 12 Volt Planet

www.12voltplanet.co.uk

If you want to know the size of the existing cable, it is often stamped on the outside at regular intervals. A torch shining at a shallow angle will make it easier to see.

Thanks for that. Very informative. I just wanted to purchase cable of the same size as what it there and buying online it is so difficult to tell size. I thought 16mm would be the diameter and that did strike me as a bit over the top. - the above explains that.