gsm
Advanced Member
E-Trek AGM Battery Re-Configuration
1 - Sorry the pictures did not come trough. There is really nothing too earth shacking in them, but an illustration is worth a thousand words. I am very new at all this. I tried once again to send the pictures with this post, but I failed. I should also have numbered the paragraphs in my texts to make life easier for all.
NOTE – Markopolo –-- There is one problem with the red wiring in your schematic. The chassis ground on E- must be removed.
2 - I Should have explained why believe that in the series connection of the four, six-volt battery-blocks ( AB, EF, CG and DH), the hotter battery-block AB will consistently charge more quickly and reach full charge before the others when the blocks all experience the same charging current. Assuming four equally healthy blocks start charging from the same charge-state.
4 - The reason is that charging efficiency varies with battery temperature, in the range of 80 to 90 percent, over the temperature band mainly of concern to us.. It may be greater on some products than on others. This means that only 80 to 90 percent of the charging-current through the four battery-blocks is given over to the battery charge-state. Since the charging efficiency depends directly on chemical activity within the battery it will increase with temperature. The rule of thumb frequently used states that chemical activity roughly doubles every 10 degrees Celsius (21.2 degrees Fahrenheit) in temperature increase.
4 - This means that over the same charging period, the hotter battery-block AB will accumulate a higher state of charge than the colder battery-blocks, even though all are subject to the same charging current. And battery-block AB will reach the fully charged state first. At that time battery-blocks EF, CG and DH still have not reached full-charge, and if left that way for a prolonged period every usage-cycle, the capacity of the three colder blocks will decrease due to sulfation. I estimate that under these conditions right from the outset, the 24 volt battery-system would have the maximum Amp-Hr capacity effectively reduced by five to 10 percent. With each cycle the AB battery-block would begin charging from a higher charge-state, reach full charge earlier, and at charging cut-off leave blocks EF, CG and DH less and less fully charged.
5 - If the fully charged state of the AB battery-block is used as the determining factor for ending the charging process of the 24-volt battery system the system, six of the eight batteries will go into relatively rapid performance decline.
6 - That is why I asked whether Booster could confirm from his experience whether a bit of over charging is less harmful to AGM batteries then undercharging. The approach to exploit the economy of sticking with the exiting eight batteries is dependent on this. Booster basically confirms that it is likely possible for AGMs to bear some small period of over-charge. From this it appears that it is worth a try to allow the AB block to overcharge, and focus on the charge-state of the other three blocks.
7 - This why I recommended allowing a degree of overcharge of the AB block each cycle, to ensure that the three blocks EF, CG and DH are fully charged. This essentially happens if battery state of charge is sensed at the 24 volt terminal. I previous touched on this, and recommending that
battery temperature sensing be done at a terminal centrally located in the battery-nest at the rear, most likely the warmest spot back there. This will raise the charging source voltage, favoring fully charging the colder three blocks.
NOTE: - It would take a very complex battery-balancer with temperature sensing for each to the four battery-blocks to account for this, bypass the unnecessary current from block AB, and put it into the other three blocks.
Boosters idea of using six, Eight-Volt batteries in the rear compartment.
8 - I like Boosters idea of using Six eight-volt, 160 Amp-Hr AGMs, They could be quite large, and fill the entire floor area of the battery-compartment. The floor space is one limit, but the batteries could be a few inches taller, i.e. come above vehicle-floor with an appropriate sealed cover/hood. Venting to the exterior would remain below floor. Suitable taller batteries of greater Amp-Hr rating might be found and installed, with some sacrifice in storage space.
9 - One of the advantages of Booster's approach to the 24 volt battery system is that the series connected under-hood batteries A and B can be retained. This allows those batteries to continue as the prime or backup 12 volt system. It also gives the coach a backup starter-battery. The A and B batteries would be charged the conventional ways.
10 - One might view the 24 volt to 12 volt converter as optional or as an independent source, when a second isolated 12 volt source is advantageous, or a back up is needed. One is no longer seriously impacted by a 12 volt system failure.
11 - If possible at least two of the six batteries might kept healthy as replacements for A and B when needed. All six batteries might be used in a small power back- up system. Waste not want not.
Three Pictures and a Schematic should follow
Regards All
GerryM
1 - Sorry the pictures did not come trough. There is really nothing too earth shacking in them, but an illustration is worth a thousand words. I am very new at all this. I tried once again to send the pictures with this post, but I failed. I should also have numbered the paragraphs in my texts to make life easier for all.
NOTE – Markopolo –-- There is one problem with the red wiring in your schematic. The chassis ground on E- must be removed.
2 - I Should have explained why believe that in the series connection of the four, six-volt battery-blocks ( AB, EF, CG and DH), the hotter battery-block AB will consistently charge more quickly and reach full charge before the others when the blocks all experience the same charging current. Assuming four equally healthy blocks start charging from the same charge-state.
4 - The reason is that charging efficiency varies with battery temperature, in the range of 80 to 90 percent, over the temperature band mainly of concern to us.. It may be greater on some products than on others. This means that only 80 to 90 percent of the charging-current through the four battery-blocks is given over to the battery charge-state. Since the charging efficiency depends directly on chemical activity within the battery it will increase with temperature. The rule of thumb frequently used states that chemical activity roughly doubles every 10 degrees Celsius (21.2 degrees Fahrenheit) in temperature increase.
4 - This means that over the same charging period, the hotter battery-block AB will accumulate a higher state of charge than the colder battery-blocks, even though all are subject to the same charging current. And battery-block AB will reach the fully charged state first. At that time battery-blocks EF, CG and DH still have not reached full-charge, and if left that way for a prolonged period every usage-cycle, the capacity of the three colder blocks will decrease due to sulfation. I estimate that under these conditions right from the outset, the 24 volt battery-system would have the maximum Amp-Hr capacity effectively reduced by five to 10 percent. With each cycle the AB battery-block would begin charging from a higher charge-state, reach full charge earlier, and at charging cut-off leave blocks EF, CG and DH less and less fully charged.
5 - If the fully charged state of the AB battery-block is used as the determining factor for ending the charging process of the 24-volt battery system the system, six of the eight batteries will go into relatively rapid performance decline.
6 - That is why I asked whether Booster could confirm from his experience whether a bit of over charging is less harmful to AGM batteries then undercharging. The approach to exploit the economy of sticking with the exiting eight batteries is dependent on this. Booster basically confirms that it is likely possible for AGMs to bear some small period of over-charge. From this it appears that it is worth a try to allow the AB block to overcharge, and focus on the charge-state of the other three blocks.
7 - This why I recommended allowing a degree of overcharge of the AB block each cycle, to ensure that the three blocks EF, CG and DH are fully charged. This essentially happens if battery state of charge is sensed at the 24 volt terminal. I previous touched on this, and recommending that
battery temperature sensing be done at a terminal centrally located in the battery-nest at the rear, most likely the warmest spot back there. This will raise the charging source voltage, favoring fully charging the colder three blocks.
NOTE: - It would take a very complex battery-balancer with temperature sensing for each to the four battery-blocks to account for this, bypass the unnecessary current from block AB, and put it into the other three blocks.
Boosters idea of using six, Eight-Volt batteries in the rear compartment.
8 - I like Boosters idea of using Six eight-volt, 160 Amp-Hr AGMs, They could be quite large, and fill the entire floor area of the battery-compartment. The floor space is one limit, but the batteries could be a few inches taller, i.e. come above vehicle-floor with an appropriate sealed cover/hood. Venting to the exterior would remain below floor. Suitable taller batteries of greater Amp-Hr rating might be found and installed, with some sacrifice in storage space.
9 - One of the advantages of Booster's approach to the 24 volt battery system is that the series connected under-hood batteries A and B can be retained. This allows those batteries to continue as the prime or backup 12 volt system. It also gives the coach a backup starter-battery. The A and B batteries would be charged the conventional ways.
10 - One might view the 24 volt to 12 volt converter as optional or as an independent source, when a second isolated 12 volt source is advantageous, or a back up is needed. One is no longer seriously impacted by a 12 volt system failure.
11 - If possible at least two of the six batteries might kept healthy as replacements for A and B when needed. All six batteries might be used in a small power back- up system. Waste not want not.
Three Pictures and a Schematic should follow
Regards All
GerryM
