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Old 22nd April 2013, 04:07 PM   #11
FoMoCo is offline FoMoCo  United States
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Originally Posted by MarianB View Post
@FoMoCo i think you might be right, but i am not worried by that for 2 reasons: 1-I will never let the UPS's battery backup the PC more than 5 to 10 mins max, as soon as the line drops i instantly hit the shutdownd command on the PC, so in fact it only has to cope with less than 5 mins... and the 2'nd reason is that as i sayd i plan to modify completly my UPS, i will design a new converter using a ferrite core and make sure to get as high eff as possible from it, it is much work i know but i am not worried by that.
If you only need 5 minutes, why modify anything?
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Old 22nd April 2013, 05:02 PM   #12
MarianB is offline MarianB  Romania
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because of what i have sayd earlyer, the efficiancy it's ridicoulus, actually a bit under 50%, that is unacceptable, i am sure it can do way better, also i can desighn the charging circuit exactly the way i want to.
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Old 22nd April 2013, 05:18 PM   #13
Mooly is offline Mooly  United Kingdom
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Your numbers sound about right. A 40Ah batteryrunning for 80 mins is 0.5Ah per minute capacity used.

I'm not 100% sure how well car batteries tolerate 24/7 float charging. If your designing your own charger then I would perhaps arrange it to cut out after say 18 hours if it applies around 13.8 volts and to cut in every 7 days or so or whenever a mains interruption occurs.
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Old 22nd April 2013, 05:34 PM   #14
MarianB is offline MarianB  Romania
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Wouldn't it be easyer to just set up a monitoring circuit that cut's off the charger after reaching about 14,4V on the battery? this way i can ensure that the battery would not have to handle permanent charging, just recharging when needed, i could also provide some histeresis on the on/off charger thresholds if needed.

LE: @kenpeter, i keep my battery outside so it is well ventilated, also far from the UPS and any spark source, i am using heavy duty cables and conectors to get the power to the UPS.
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Old 22nd April 2013, 05:44 PM   #15
Mooly is offline Mooly  United Kingdom
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That doesn't work in practice.

14.4 volts or even higher voltage can be reached very quickly but the battery is still drawing substantial current that tapers down as the battery charges.
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Old 22nd April 2013, 06:02 PM   #16
MarianB is offline MarianB  Romania
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Then the monitoring circuit can be set up to "read" the current drawn by the battery as it is charging and when it reaches a set vallue it cut's off the charger, or some combination of both current and voltage, whatever you think it is best cus i do not want to complicate stuff timing it...
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Old 22nd April 2013, 06:44 PM   #17
Mooly is offline Mooly  United Kingdom
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Exactly... keep it simple

Measuring the current is problematic because it varies greatly with temperature and the condition of the battery as it ages.

Applying a known voltage for a certain minimum time has to be the simplest solution.
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Old 22nd April 2013, 06:51 PM   #18
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There's yet another reason why car batteries / starter batteries (flooded type) won't make you happy.
They need the vibrations from the road to stay healthy !
If kept stationary the electrolyte will separate over time, sulfuric acid being denser than water it will accumulate on the bottom and pure water on top. Plate corrosion is going to happen even with trickle charge.
Some float chargers apply a very high charge current (and voltage) once per day to deliberately cause gassing, the bubbles stirring the mixture. But I haven't seen any data on that yet.
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Old 22nd April 2013, 06:51 PM   #19
MarianB is offline MarianB  Romania
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@Mooly, but as i understand if the battery draws no or little current it means it is charged... am i wrong?

If allowing your suggested solution then how do i go about the timing circuit? i think it would be too complicated to be worth it...

@payloadde, good point and yet another reason to drop the ideea but still this battery has done it's job good enough despite the UPS's low efficiency, looking at batteryes prices all i can afford of the deep cycle stuff is arround 10-12Ah capacity...
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Old 22nd April 2013, 07:09 PM   #20
Mooly is offline Mooly  United Kingdom
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Originally Posted by payloadde View Post
There's yet another reason why car batteries / starter batteries (flooded type) won't make you happy.
They need the vibrations from the road to stay healthy !
If kept stationary the electrolyte will separate over time, sulfuric acid being denser than water it will accumulate on the bottom and pure water on top. Plate corrosion is going to happen even with trickle charge.
Some float chargers apply a very high charge current (and voltage) once per day to deliberately cause gassing, the bubbles stirring the mixture. But I haven't seen any data on that yet.
Interesting thought. I've never heard of that and it sounds plausible although batteries I have seen all have movement of the electrolyte when fully charged and even slight gassing occurs.

Interesting non the less...

Quote:
Originally Posted by MarianB View Post
@Mooly, but as i understand if the battery draws no or little current it means it is charged... am i wrong?

If allowing your suggested solution then how do i go about the timing circuit? i think it would be too complicated to be worth it...

@payloadde, good point and yet another reason to drop the ideea but still this battery has done it's job good enough despite the UPS's low efficiency, looking at batteryes prices all i can afford of the deep cycle stuff is arround 10-12Ah capacity...
The timing circuit you would have to design. Something like a CMOS oscillator and divider chip (4040 and 4060 chips from memory) perhaps with diode gating on the appropriate outputs to get something like the charge time required. Or a simple mechanical timer if it outside, the sort with pegs in to set the on and off times.

The only correct way to really determine the state of charge is to measure the specific gravity of the electrolyte but that's not practical.
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