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12v rail for work bench needs battery what kind of controller I need?

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jpoopdog

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Basically to power various lights and e4c im setting up something similar to a 12v outlet around my workbench, I also want to power a 24v fridge. Problem is that the 6-8A Spike when it first turns on is too much even though the psu is 15A and I've gotten it to 13A ok. I'll have a battery hooked up in parallel either for everything or just the fridge, do I need any kind of particular controller? Or would diodes be ok? The sole function is to prevent the current protector from tripping. The fridge otherwise uses very little power and is constantly on low using like 2-3A. It runs through a converter to have 24v as it lessens the Spike , it runs nicer at 24v than 12v.

The whole problem here is that if it ever was to turn off it couldn't turn itself back on again, such as if there was ever a momentary blackout or the plug comes out I sometimes step on it and do t realise I've disconnected it. The current psu is not ideal for the job. It's a pc atx and its not something I can build onto the desk descretely, plus it's Rusty and doesn't look too safe.


I also often like to mess with high voltage stuff and need to use a battery to avoid shocking my bench top supply, and other miscellaneous uses. The battery I have in mind is only 6Ah and again is just for momentary surges but should be available always. How should I have this set up? Im only after a cheap or simple controller I think an mppt might be what I need. Or could I just always have it in parallel with some diodes or something to prevent current going back when it's off. I think I can adjust the voltage up to 13v with a trimpot.
 

spec

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Hi JPD,

Not too sure what your set up is, but I think that some high value, low ESR, capacitors across the 12V supply line will fix your problem. Just keep adding more and more capacitors until the problem goes away.:)

spec
 

MikeMl

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It takes huge, expensive capacitors to come close to what a small SLA can do to solve your start-up inrush problem.
 

Les Jones

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I suggest that you connect the 12V SLA battery to your 12 volt line via a high current schottky diode and have the SLA battery connected to a low current float charger. You will probably have to adjust the 12 volt supply to give about 13.4 volts so the SLA can be at it's float charge voltage of 13.8 volts without supplying current into your nominal 12 volt rail. Alternatively you could use two silicon diodes in series to give a 1.4 volts drop provided the fridge would tolerate a slight drop in voltage at switch on. By the way what is an "e4c" ?

Les.
 

dr pepper

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To do it properly you'd use a multi stage charge controller ic in conjunction with the pc power supply.
The ic would bulk charge the battery, then maintain a float charge until the load pulls the o/p down and then it would switch back to bulk charge, a multi stage because of its design is current limiting so would protect to a degree itself and the supply.
Get yourself a server power supply, you see them cheap on ebay, just make sure it comes with a fan if required.
 

spec

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Here is another approach. The capacitor is only nominal and could probably be a much lower value, say 1mF (1,000uF). The circuit limits the fridge current to 10A. The current limit can be changed by altering the value of R15 according to the formula, Ik= 0.6V/R15. The best approach would be to make R15 as large as possible, consistent with the fridge starting satisfactorily.

2016_11_01_ETO_12V_FRIDGE_CURRENT_LIMIT.png
 
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spec

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It takes huge, expensive capacitors to come close to what a small SLA can do to solve your start-up inrush problem.
This is true. I didn't realise how big the capacitor would need to be (5F). But all the same, a hefty capacitor across the 12V line would be a good move.

spec
 
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