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Forum Index : Electronics : Lead-acid boost/float current
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| davef Guru  Joined: 14/05/2006 Location: New ZealandPosts: 499 |
On my 24Volt battery (8*6V 220AH) I typically get between 2.0 and 2.5Amps during boost and float. Could anyone suggest what typical boost/float currents would be for new batteries with a capacity of 440AH? Thank you, davef |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Dave Your boost and float current is voltage dependent at 27.5 float 2 - 3 amps sounds about right at boost it should go to about twice the float current at around 30 volts On my battery bank I have just re-hydrated it is 2.5 amps at 27.5 and if I go to boost it goes to 5.5 amps that is on a 750 AH bank, these batteries are 15 years old and where heavily sulfated so I was going for 32 volt and desulphators to get the sulfate reconstituted, so it may be a bit different to your new set. You should follow the makers boost and float voltage recommendations with a weekly equalization charge to 32 volts for a couple of hours to break down residual sulphation, or fit desulphators that do the job at float voltages and use less water and energy and are generally easier on the batteries. A lot of the so called experts say they do not work but I have found they are really good at extending battery life and saving on boiled out electrolyte due to high voltage equalization. All the best Bob Foolin Around |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Bob, I have a Tracer solar controller to do the battery management. Equalisation is factory-set at 29.6Volts. In any case I couldn't go above 30.4V or my power inverter will shut-down. I have built and use a 12V desulphator on another battery system. I tried to modify it for 24V operation and only succeeded in blowing up several FETs. What prompted by question is that 2.5Amps at 27.5Volts for a number of hours a day is "wasted energy". Perhaps that is the price for keeping batteries in good condition. Thank you for supplying some figures that seem to indicate my batteries are behaving normally. Cheers, Dave |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Dave It is a bit of a waste of power but in my experience over the years it is common to loose 10% of input to various inefficiencies across the RE system. The 32 volt equalization is a theoretical voltage where all the sulphation is desolved and if that is done it is supposed to stop the slow deterioration of lead acid batteries over a number of years, in practice I have found that using desulphators achieves this end without boiling hell out of the batteries, your comment on blowing the desulphator on 24 volts is unfortunate but you can use two 12 volt units across the bank with even better results that a single 24 volt unit. An actual meter reading on a 500 AH 24 volt bank I am re hydrating at 29 volts. 
An actual meter reading on a floating at 27.5 volts, also re hydrating. 
In the battery rescue thread I have also included the circuits of a 12 and 24 volt desulphator, they come highly recommended, I am getting the bits together to build a few 12 volt versions as I found that they work better than going across the 24 volts, on a new battery set i think the 24 volt one would be OK but in my case my battery bank needed a bit more to bring it back up as it had dehydrated over the last 15 years and the reclaiming has been a bit of a drag but is working. All the best Bob Foolin Around |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
I have started desulphating by "cycling" the one unit I have around the 8 * 6Volt batteries. I have read some of that thread but will start at the beginning and read the whole 34 pages. The unit I built is based on a Cap-doubler version I found on a desulphator forum. Thanks again. Dave |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Dave How about sharing the desulphator circuit with us as it is always interesting to try different ways to desulphate batteries. My friend built one from a CDI ignition module driving a small Ferrite transformer 12 volt to 240 volt, driven by a 555 IC unfortunately I never got the circuit off him. All the best Bob Foolin Around |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Voltage doubler desulphator Not as many pages as the battery rescue thread :) I use a microprocessor to drive the output stages. Also, note the modification of a series diode in the drain of the FETs. Evidently, to eliminate a turn-on current surge. If you want pictures and/or ATMEL ATmega88 code just say so. Dave |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Dave Thanks for the link to the desulphaters very interesting reading, I think a combination of the original circuit and the output of that one would be a winner, thanks for the offer of the micro driver module but I think that's a bit beyond the old buggers capability the 555 circuit is about as complicated as I can can understand. I did my time on valves and high voltage and these little IC things are stretching my capability to nearly breaking point. I have most bits to have a go at this one and even a box of 100UH inductors so I will have a go and see if I can get any magic smoke. All the best Bob The battery rescue thread has gone on for a few years now, maybe I should start a new one when I Finnish these batteries I am doing now. Foolin Around |
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