Changing from 12v battery bank(8 Batteries) to 24v. How to wire them?

[foo]

I saw a post about wiring 6 batteries but not on how to wire 8 batteries.
Does anyone have a schematic or drawing on how I should do this?

My guess is that I will make 4 strings of 2 batteries connected in series.
Then wire the positives of those 4 strings in parallel while also having the negatives of the 4 strings wired in parallel as well.

Thanks for any information.

Cheers!

[inetdog]

My guess is that I will make 4 strings of 2 batteries connected in series.
Then wire the positives of those 4 strings in parallel while also having the negatives of the 4 strings wired in parallel as well.

You guess correctly. The only remaining Gotcha is that you will need to use a bus bar for positive and another for negative to allow you to keep all of the cable lengths and connection resistances the same.
Four strings in parallel can be done, but it is far from ideal.
If you did not already have the batteries the solution would be to use 6V, 4V or 2V batteries (higher AH per battery while keeping a reasonable size) instead to get either one string or two strings.

Look at this site http://smartgauge.co.uk/batt_con.html for diagrams and warnings how not to do it.

[foo]

Thank you for the link and added information.

[hankuru5ki]

how many strings is safe

You guess correctly. The only remaining Gotcha is that you will need to use a bus bar for positive and another for negative to allow you to keep all of the cable lengths and connection resistances the same.
Four strings in parallel can be done, but it is far from ideal.
If you did not already have the batteries the solution would be to use 6V, 4V or 2V batteries (higher AH per battery while keeping a reasonable size) instead to get either one string or two strings.

Look at this site http://smartgauge.co.uk/batt_con.html for diagrams and warnings how not to do it.

Good morning inetdog,

The link above may have suggested that it is possible to connect as many 8 'strings' as so long "they are balanced." But here you suggested to perhaps limit to only one or two strings and I am curious as to which safety issue may anything more than 2 strings may pose a potential hazard?

My system has three strings connected as method II ("why?" Because I just now have known of the other method 3 & 4 from smartgauge and thanks to the link you've provided) and I am a bit concern with the "ideal" of limited to only 1 or 2. Many thanks in advance for clarifying.

[SunEagle]

Good morning inetdog,

The link above may have suggested that it is possible to connect as many 8 'strings' as so long "they are balanced." But here you suggested to perhaps limit to only one or two strings and I am curious as to which safety issue may anything more than 2 strings may pose a potential hazard?

My system has three strings connected as method II ("why?" Because I just now have known of the other method 3 & 4 from smartgauge and thanks to the link you've provided) and I am a bit concern with the "ideal" of limited to only 1 or 2. Many thanks in advance for clarifying.

The main reason to limit the number of parallel wired batteries is due to the potential of not charging or discharging the all equally. Even a very small difference in resistance in each "string" will cause the amount of charging amps to be different from the other "strings". That will cause one string to become more dominant and the others to get less. That ends up causing an out of control spiral with one string dieing quicker than the other ones.

Final outcome is like one bad apple spoils the bunch. Once you have a "bad string" the others quickly follow.

Increasing the number of "strings" increases the chance of "bad apples".

[hankuru5ki]

Da Strings Theories

The main reason to limit the number of parallel wired batteries is due to the potential of not charging or discharging the all equally. Even a very small difference in resistance in each "string" will cause the amount of charging amps to be different from the other "strings". That will cause one string to become more dominant and the others to get less. That ends up causing an out of control spiral with one string dieing quicker than the other ones.

Final outcome is like one bad apple spoils the bunch. Once you have a "bad string" the others quickly follow.

Increasing the number of "strings" increases the chance of "bad apples".

When a "Fanatic" has spoken I guessed that kinda closed the deal... many thanks to all U-Gurus wished I have found you folks sooner, but better later than never.

[lkruper]

The main reason to limit the number of parallel wired batteries is due to the potential of not charging or discharging the all equally. Even a very small difference in resistance in each "string" will cause the amount of charging amps to be different from the other "strings". That will cause one string to become more dominant and the others to get less. That ends up causing an out of control spiral with one string dieing quicker than the other ones.

Final outcome is like one bad apple spoils the bunch. Once you have a "bad string" the others quickly follow.

Increasing the number of "strings" increases the chance of "bad apples".

What do you think about the way Samlex has their 2 or 3 bank chargers set up? I know that they isolate the banks with diodes to make sure they cannot charge/discharge each other, but they don't individually control the charging volts/amps. Would they have the same problem as a parallel battery bank?

[Willy T]

The samlex manual gives you a big hint. Boat Manufactures try to take the cheap way out with 2,3,4 bank chargers, they seldom work out because the two engine batteries, generator and house bank are seldom at the same soc. They must have some kind of time out with a load with the dip switch setting , as long as it works.

Charging more than one bank of batteries

CAUTION! When charging more than one
bank of batteries at the same time using
3 Stage Charging, ensure that the batteries
in the banks are in a similar discharged
condition. If one bank is completely
discharged and another is almost fully
charged, the bank that is fully charged
will be subjected to over charge condition
during the time when the charger remains
in Boost Stage for charging the completely
discharged bank. If batteries are in dissimilar
states of charge, select DIP Switch
setting for "Battery with Load."

[lkruper]

The samlex manual gives you a big hint. Boat Manufactures try to take the cheap way out with 2,3,4 bank chargers, they seldom work out because the two engine batteries, generator and house bank are seldom at the same soc. They must have some kind of time out with a load with the dip switch setting , as long as it works.

Charging more than one bank of batteries

CAUTION! When charging more than one
bank of batteries at the same time using
3 Stage Charging, ensure that the batteries
in the banks are in a similar discharged
condition. If one bank is completely
discharged and another is almost fully
charged, the bank that is fully charged
will be subjected to over charge condition
during the time when the charger remains
in Boost Stage for charging the completely
discharged bank. If batteries are in dissimilar
states of charge, select DIP Switch
setting for "Battery with Load."

Yes, I saw that. In the application I am considering, I would have two or three batteries which would all be charged and discharged at the same time with the same load. What I do not fully understand at this point is if this caution results from the same phenomenon as batteries in parallel. If it does, then I will not consider this option.

[SunEagle]

Yes, I saw that. In the application I am considering, I would have two or three batteries which would all be charged and discharged at the same time with the same load. What I do not fully understand at this point is if this caution results from the same phenomenon as batteries in parallel. If it does, then I will not consider this option.

The samlex probably has a common buss where you could connect multiple batteries. There chance of one set of battery connections having a higher resistance then the other is low. (unless you use different size & length of wire)

But with a larger number of parallel wired batteries using cables and connectors at the batteries the chances of different resistances is much higher. Add the connection resistance to the internal battery resistance and the total difference between "strings" could be a lot.

Sort of Russian roulette. One round out of 6 chambers is dangerous. 4 rounds out of 6 is good bye.

And to hankuru5ki.... The title "Fanatic" is something the Forum software has chosen based on the high number of my posts (some of those posts might be useful but most of the others ????)

[lkruper]

The samlex probably has a common buss where you could connect multiple batteries. There chance of one set of battery connections having a higher resistance then the other is low. (unless you use different size & length of wire)

But with a larger number of parallel wired batteries using cables and connectors at the batteries the chances of different resistances is much higher. Add the connection resistance to the internal battery resistance and the total difference between "strings" could be a lot.

Sort of Russian roulette. One round out of 6 chambers is dangerous. 4 rounds out of 6 is good bye.

And to hankuru5ki.... The title "Fanatic" is something the Forum software has chosen based on the high number of my posts (some of those posts might be useful but most of the others ????)

What about the classic problem of batteries in parallel when one battery is weak?

[SunEagle]

What about the classic problem of batteries in parallel when one battery is weak?

Same issue. A weak battery has a different internal resistance than a strong battery.

So even with the samlex charging weak and strong batteries at the same time is not healthy.

[lkruper]

Same issue. A weak battery has a different internal resistance than a strong battery.

So even with the samlex charging weak and strong batteries at the same time is not healthy.

Then I think I will eliminate the multiple bank chargers from my strategy.

[SunEagle]

Then I think I will eliminate the multiple bank chargers from my strategy.

Or come up with a plan that allows you to select 1, 2 or 3 batteries to be charged based on their SOC and age.

You might be able to use simple DC switches to isolate one battery bank from the charger but still allow you to have the ability to get 3 charged at the same time.

It comes down to cost and how much flexibility you want for your system.

[hankuru5ki]

The samlex probably has a common buss where you could connect multiple batteries. There chance of one set of battery connections having a higher resistance then the other is low. (unless you use different size & length of wire)

But with a larger number of parallel wired batteries using cables and connectors at the batteries the chances of different resistances is much higher. Add the connection resistance to the internal battery resistance and the total difference between "strings" could be a lot.

Sort of Russian roulette. One round out of 6 chambers is dangerous. 4 rounds out of 6 is good bye.

And to hankuru5ki.... The title "Fanatic" is something the Forum software has chosen based on the high number of my posts (some of those posts might be useful but most of the others ????)

I hoped you're not taking that as the wrong way...I would be dammed proud to be called a "Fanatic." The fact that you folks stick around long enough and stacked up all them posts to help others (or not) is commendable and ought to get paid for or some kinda bonuses.