Battery Charging Unit and PSU

Radio Equipment, Generators, Decontamination gear....
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Dubmatix
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Battery Charging Unit and PSU

Post by Dubmatix » Wed Dec 10, 2008 8:04 pm

Here , for reference are some pictures of my Frako PSU that came with the van. It works, as i have a mains hook up to run all the original electrics....with a couple of mods! :D

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Where it sits
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Dubmatix
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Re: Battery Charging Unit and PSU

Post by Dubmatix » Sun Jul 26, 2009 4:35 pm

Well i have been messing around with this again, the second battery seemed to be charging very slowly so been checking the circuit out.

The adjuster knob under the perspex plate adjusts the Volts per Cell (V/C) or (V/Z) in German. It was set to 2.23V per Cell (6 cells so Vout is 2.23Vx6 =13.38V). Now this is all well and good, but there are a pair of power diodes between the charger and the batteries. The diodes have a volt drop of 0.72 V so the batteries see Frako Vout - Diode Vdrop = 13.38V-0.72V = 12.67V. This meant that my flat 80Ah battery was charging at 300mA!! which would take a LONG time to charge!

Switched to the higher setting to increase Vout and this has had the effect of upping the charge current to 1A. This is better though i have considered using an alternative diode with a lower voltage drop (Vf) of about 0.4V .

This would allow switching to the faster rate when required with a bit more charge current and still have the lower range trickle charge for longer charging. I guess this unit is designed primarily for topping up the battery and supplying bulk current to run the Radios, Eberspacher etc.
Of course the outputs of the Frako are tweakable and the possibility of tweaking up the top range to take the Diode V drop into account may be an option to consider...though there are two pots per channel and i am not sure of what both do!

One other item to note is that one of the blocker diodes has been cooked in the past as there is black charring above it. The replacement in a different type and hopefully it is up to the job! I can't see the part number without removing it!

I'll se how this 4-5 day charge goes (although i know the current will go down as it charges..) and take it from there.

That's all for now!

John

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