Re: power suppliers

Hi Guys,

William raises a good point that most people forget: these kind of batteries 
need to be charged at 13.8V to avoid damage and since we are talking about 
UPS type functions, after a deep discharge, need a high current for the 
first couple of hours!


-----Original Message-----
From: [email protected] [mailto:[email protected]] On 
Behalf Of William Stucke
Sent: 22 May 2014 12:07 AM
To: IOZ
Subject: Re: [IOZ] power suppliers

Hi Daniel,

An interesting post, but 1 amp is only sufficient to charge a pretty small 
battery. However, if you're talking about float charging, then  1 amp is 
plenty for a very large 1000 Ah battery (based on 0.001xC, where C=battery 
capacity in Ah). Do not exceed 0.20xC as the initial charge current - thus a 
1 amp supply shouldn't be used on a battery of less than 5 Ah capacity. The 
correct float charge voltage at 20 degrees C is 2.26 - 2.31 V per cell, 
dropping to 2.24 - 2.29 V per cell at 30 degrees C.

The recommended cycle charge voltages are 2.43 - 2.53 V and 2.37 - 2.47 V 
per cell, respectively.

A fully charged Lead-Acid battery produces 2.15 V per cell, thus a "12 V" 
battery - like your Marine battery example - would have an open circuit 
voltage of 13.56 V when fully charged. It may have a  slightly higher value 
immediately after taking it off the charger. The discharged voltage is 1.94 
V per cell, so the battery voltage would be 11.64 V. Again, this will 
usually recover somewhat when the load is removed. Your charging voltage of 
12.6 V is thus a little low, although quite safe. Hint: if your car battery 
shows less than 12 V on your multimeter, it's either flat or dead.

Typical good quality sealed Lead-Acid batteries lose about 3% of their 
capacity per month at room temperature. At 20 degrees, it will have 60 - 70% 
of its capacity after one year. A single charge per year of an unused 
battery is sufficient to keep it in good condition. Always charge it when 
you first get it - you have no idea how long it's been on a shelf somewhere.

A typical "12 V" power supply produces about 18 V on an open circuit. While 
rated at 1 A, they will also usually produce a bit more than that, and have 
very little in the way of protection. Connecting one directly to a flat 
battery is a good way to blow it!

Some more useless information for you ;-)

I can post the complete technical paper if you want - 16 pages and 161 KB. 
It contains a number of charging circuit diagrams, over-discharge 
protection, etc. and explains the concepts very well.

Kind regards,

William Stucke
ICASA Councillor
011-566-3009

-----Original Message-----
From: [email protected] [mailto:[email protected]] On 
Behalf Of Daniel Schroder
Sent: 21 May 2014 06:18 PM
To: IOZ
Subject: Re: [IOZ] power suppliers

Those power supplies are gold in a post eskomolyptic world with battery 
backed essential services, but eskom is confident there no problems. Well 
other than the 57b zar bailout .. This year.

My point is they perfect for car battery / inverters to a 224  volt supply, 
to backup systems.

If your load to the step up inverter/transformer is 12 volt + .6 volts via a 
diode that runs from the power supply. You also have a single marine battery 
supplying 12.4 volts via a diode to the same load. While ac powerered supply 
is active , the battery is latent unless there is no ac then battery takes 
over instantly since no more resistance, or is at a lower voltage.

To keep battery charged a diode and a resister is run from the ac supplied 
12.6v power to the battery using a diode and resistor to keep power flowing 
at a certain voltage, 12.4 v to prevent overcharging and keep battery 
charged, while not interfering with primary power supply.

In summary ac supplied 12.6 v is fed straight into the load of target 
device. With a resistor and another diode 12.4 and below is fed to the 
battery as well. When battery discharges it's kept topped up at 12.4v.
Primary ac dips below 12.4 battery takes over. Immune to brownouts as well.

You will need to do some math to figure out carried load amperage fuses etc 
but it's the gist. The voltages I used are just for reference, you will need 
a voltmeter.

Its a lot more fun than buying a ups which are ironically doing a lot better 
job of what I described above, but useless after half a year.

Just my input
Daniel


On 21 May 2014 4:41 PM, "Saul" <[email protected]> wrote:
>
>
>    Hi All,
>
>    This might sound like a strange post but...
>
>
>    A while back we did a large install of numbers AP, the result is that
>    we now have a few large boxes of power supplies that we don't need.
>
>    OUTPUT 12V 1A
>
>
>    Option 1 is to simply put them in the bin, but that isn't very eco
>    friendly
>
>    Option 2: Ideas anyone?
>
>
>    Is there anyone that would want such a thing?
>
>
>
>
>   Regards,
>
>
>
>
>
>   Saul Stein
>
>   Technical Manager
>
>   Phone:
>
>         +27 (0)21 421 9857
>
>   Fax:
>
>         +27 (0)21 425 4537
>
>   Cell:
>
>         +27 (0)82 908 5553
>
>   Email:
>
>         [1][email protected]
>
>   Web:
>
>         [2]www.enetworks.co.za
>
>                                eNetworks
>
>                                                      where service is
everything
>
>                                                         A Datacentrix
company
>
>
>
>                                   eNetworks
>
>    |
>
>                                  PO Box 2534
>
>    |
>
>                                   Cape Town
>
>    |
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>                                 South Africa
>
>    |
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>                                     8000
>
>                                                    2013 HP GOLD
> Specialist
>
> References
>
>    1. mailto:[email protected]
>    2. http://www.enetworks.co.za/
>
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