About to mount and connect the second 100 ah battery in parallel with the 100ah already in use. What cable size should I use?

Aussie Paul. 

Paul I don't know what the others will say but I will tell you to fit the Biggest Cables you can..

I would run 50mm - 75mm as a minimum..

-- the best way to reduce any issues..

--

Paul the connection on the Left is the Best way to connect the 2 Batteries to system...

-- Make sure the Cable Link'n both batteries large enough to not be affected by voltage drop..

Juergen

Just one VERY enjoyable snippet..

Lifespan of batteries

The lifespan of a deep cycle battery will vary considerably with how it is used, how it is maintained and charged, temperature, and other factors. In extreme cases, it can vary to extremes AGMs can be killed in less than a year by severe overcharging. Gelled cells batteries can be destroyed in one day when overcharged with a large automotive charger. Golf cart batteries can be destroyed without ever being used in less than a year because they were left sitting in a hot garage without being charged. Even the so-called dry charged (where you add acid when you need them) have a shelf life of 18 months at most. They are not totally dry they are actually filled with acid, the plates formed and charged, then the acid is dumped out.

These are some typical (minimum maximum) typical expectations for batteries if used in deep cycle service. There are so many variables, such as depth of discharge, maintenance, temperature, how often and how deep cycled, etc. that it is almost impossible to give a fixed number. But here goes anyway:

• Starting: 3-12 months
• Marine: 1-6 years
• Golf cart: 2-7 years
• AGM deep cycle: 4-10 years  >>> At what Rate of Usage.... Most AGMs have a cycle life of 800-1200[Maybe 1500] cycles [Charge - discharge] so more like 2-5yrs
  
• Gelled deep cycle: 2-7 years
• Telephone (float): 2-10 years. These are usually special purpose float service, but often appear on the surplus market as deep cycle. They can vary considerably, depending on age, usage, care, and type.
• NiFe (alkaline): 5-35 years
• NiCad: 1-20 years

So yes they seem to be an OK company But I don't think I would be Promoting them as the best source of information..

-- Paul Re the Cable size for your connection.. If it's only a very short distance Try using this site and say the cable run is 2m long..

Cable sizing

Calculate the Amperage by dividing the max Wattage of your Inverter, so if you have a 2500/5000w inverter us the 5000w and the basic voltage of you battery.. 12v instead of the 13.8 that they have in the table.. So the Max Amp's is 5000/12 = 416A

so using the Calculator you get     33.64mm3 cable size.. [but that I would think about as it has a 3.6%Lose.. I would Choice...

67.43mm2 which gives you a Lose of 1.8%  The Nearest size cable is 75mm2 Cable..

I used a 95mm2 cable for my connection from the Batteries to the Terminal Block's.. [Fuses off that terminal block]

Juergen

Food for thought....

2 things, the longer the length of cable and the 100AH will dictate the cross section of the hookup cable.

Resistance is our enemy here, as it causes volt drop and electrical enemy number one HEAT.

The formular is; Resistance equals rho (constant for wire type) times length divided by cross section area of the cable.

I would run the smallest distance between the batteries with two even three cables on each terminal (welding cables) 20mm sq at least, if the max expectation on inverter is greater than 400A peak, that is a lot of DC current and will cause big issues if this is not done properly, ere on the side of safety and caution.

Whatever you do have NO SHARP BENDS when you hook up, these bends create hot spots with higher currents. Rule of thumb is the bend should be at least 5 times the diameter of the cable.

Unfortunately there are a lot of things to think about before we go playing with cables and mid AH batteries.

Safe travels

BTW running same polarity cables together will cause attraction of the cables so they can be cable tied together, please dont do this with opposite polarities, they repel (bigger the current greater the repulsive force). 

Sorry I commented. I thought it would be a good site to help people ,  that don't understand the ins and outs of Batteries & Solar.  

Phil C wrote:

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Food for thought....

2 things, the longer the length of cable and the 100AH will dictate the cross section of the hookup cable.

Resistance is our enemy here, as it causes volt drop and electrical enemy number one HEAT.

The formular is; Resistance equals rho (constant for wire type) times length divided by cross section area of the cable.

I would run the smallest distance between the batteries with two even three cables on each terminal (welding cables) 20mm sq at least, if the max expectation on inverter is greater than 400A peak, that is a lot of DC current and will cause big issues if this is not done properly, ere on the side of safety and caution.

Whatever you do have NO SHARP BENDS when you hook up, these bends create hot spots with higher currents. Rule of thumb is the bend should be at least 5 times the diameter of the cable.

Unfortunately there are a lot of things to think about before we go playing with cables and mid AH batteries.

Safe travels

BTW running same polarity cables together will cause attraction of the cables so they can be cable tied together, please dont do this with opposite polarities, they repel (bigger the current greater the repulsive force). 

 

-- Edited by Phil C on Friday 18th of July 2014 06:58:06 PM

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 Hey Phil I think you meant Cable length and the Amps that the cable is subject to..

-- Cause I don't really see what AH has to do..

You could have a 300AH Battery bank.. and have a minimal Load of it.. and only require a small 6mm2 cable to power the load..

- So it's the Load in Amps and Distance the cable runs..

Juergen

Psst - Gold C was not jumping on your link.. Just the simple fact that All Most Battery companies care about is Selling Batteries and giving out the straight dope[Information]..

The only way you can say how long a battery will last is to ask yourself .. How Deep do you drain the battery[Depth of discharge] how often you drain/charge the batteries..

If you only use the system on weekend's, yes you will get a Good life of the batteries..  If you use the system every Day you get a short life of the batteries..

If you abuse the batteries.. Regularly take them below 50% DoD then Don't expect to get a life that is at the manufacturers spec's.. 

Thanks   Have taken a copy of sketch

Thanks everyone, I am now less uneducated than before!!!

Aussie Paul. 

Sorry guys, my bad.

What I was trying to say was a 100AH battery has the capacity for a lot of current which should be taken into consideration when hooking up in parallel.

I am dismayed by the new batteries, I was told not to take my 2 AGMs below 50%, so why the hell call them 110AH and not 55AH??

I agree that if a load is only a few mA then 6mm2 will do the trick and length wont be such a worry, BUT joining batteries in a battery install is a new can of worms, thats what I was on about.