Using old batteries with new, not possible??

Question:

recently set up a very small solar power installation at home (until then we where absolutely without electricity) consisting of a 50W solar panel and a 12V 125Ah battery. When I was browsing prices before buying this I noticed (not for the first time) that wherever I turn they tell me that there is NO-Way I can buy some batteries noe and then add some more later on when I got more money. So I started thinking , and came up with the simplest solution one can imagine. But the people I’ve asked so far could not see anything wrong with my theory witch is this: (diagram at: http://www.new-haven.org/~sido/sidoblog/2004/09/using-old-batteries-w… ) I can’t see any way these two battery-banks could affect each-others performance with this setup, if somebody can prove otherwise please let me know. — Do What Thou Wilt Shall Be The Whole Of The Law.

Response:

(diagram at:

http://www.new-haven.org/~sido/sidoblog/2004/09/using-old-batteries-w… ) I can’t see any way these two battery-banks could affect each-others performance with this setup, if somebody can prove otherwise please let me know.

     Yes, I think that will work, and I think you only need the two diodes on the positive side of the batteries, and you have to use special Schottky Diodes or you will lose too much voltage.   There are some problems with your setup: 1) There is no way to distribute the current from your two charging sources to keep both batteries charged.  If there is wind and no light you charge one battery and if there is sunlight and no wind you charge the other battery. 2) There will always be some voltage and power loss from the diode drop and the resistance of the extra equipment. 3) You have added complexity to something that should be simple.      To find out more, do a Google search on something like "battery isolation diodes".  Diode battery isolation is nothing new or uncommon, so there is a world of information out there. Vaughn

Response:

http://www.new-haven.org/~sido/sidoblog/2004/09/using-old-batteries-w…      Yes, I think that will work, and I think you only need the two diodes on the positive side of the batteries

I agree there. Ground is ground. 1) There is no way to distribute the current from your two charging sources to keep both batteries charged.  If there is wind and no light you charge one battery and if there is sunlight and no wind you charge the other battery.

 How about putting both of the charging sources into *one* buss, and from there, through diodes, to the battery banks? That would work. There would usually be voltage, and the batteries wouldn’t care from what. True, one might end up overpowering the other, the windmill probably overpowering the PV, but, then, if your biggest problem is that you have too much electricity coming in… ;-)  Tricky thing might be needing to put load diversion on *BOTH* battery banks just in case, though, as some windmill types need it… DJ

Response:

- Hide quoted text — Show quoted text – recently set up a very small solar power installation at home (until then we where absolutely without electricity) consisting of a 50W solar panel and a 12V 125Ah battery. When I was browsing prices before buying this I noticed (not for the first time) that wherever I turn they tell me that there is NO-Way I can buy some batteries noe and then add some more later on when I got more money. So I started thinking , and came up with the simplest solution one can imagine. But the people I’ve asked so far could not see anything wrong with my theory witch is this: (diagram at: http://www.new-haven.org/~sido/sidoblog/2004/09/using-old-batteries-w… ) I can’t see any way these two battery-banks could affect each-others performance with this setup, if somebody can prove otherwise please let me know.

I did something similar with a bank of random smaller batteries of different sizes,and ages(largest is 17AH.) and a few diodes. I found that a bridge rectifier has everything you need for 2 batteries,just hook it up. connect all gnds together.(common gnd) The two ~ (ac) terminals go to the the + of each batt. The + of the rectifer is your output(to loads),and the – is your charge input (solar,wind). For something large like car batteries,you’d need a large bridge rectifier,But you could make one out of 4 large diodes. (1 pair per batt) One small drawback is that the diodes will drop a bit of voltage,so your output will be a bit lower than the batteries (about 0.7V for most diodes) I actually used a bunch of high current schottky/fast diodes,which have about half the voltage drop..(~0.3V)

Response:

You will definately require a diode isolator; otherwise, you will have charging problems with different batteries, especially if they are different plate formulations and capcities.  The key will be to apply the correct temperature compensated charging voltages, as recommended by the battery manufacturers, directly across the battery posts.  For more information on increasing battery capacity, please see Section 7.3 in the Car and Deep Cycle Battery FAQ on www.batteryfaq.org. Kindest regards, BiLL…… – Hide quoted text — Show quoted text -recently set up a very small solar power installation at home (until then we where absolutely without electricity) consisting of a 50W solar panel and a 12V 125Ah battery. When I was browsing prices before buying this I noticed (not for the first time) that wherever I turn they tell me that there is NO-Way I can buy some batteries noe and then add some more later on when I got more money. So I started thinking , and came up with the simplest solution one can imagine. But the people I’ve asked so far could not see anything wrong with my theory witch is this: (diagram at: http://www.new-haven.org/~sido/sidoblog/2004/09/using-old-batteries-w… ) I can’t see any way these two battery-banks could affect each-others performance with this setup, if somebody can prove otherwise please let me know.

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