AC/DC ADAPTER and Battery

Thread Starter

superway

Joined Oct 19, 2009
125
Hello,
I would like to ask a question.

I have AC/DC adapter Class 2 Transformer 12Vdc 1000mA, and a battery 12V 4.5Ah. Can I connect them in parallel to apply 12vdc to my DUT or UUT? If there is no AC outlet near by, so I can use battery to power up my DUT, If the AC outlet isr near by, so I can power up both adapter and battery. I am not sure shoud it work or not?
If not working that way, I can install 2 circuit breakers to control battery and AC/DC adapter.
Please help

Thanks
 

wayneh

Joined Sep 9, 2010
17,496
Are you hoping to charge the battery with the transformer? Does your load require a regulated voltage?

The simple way to OR power supplies together is to just put a diode on each one to prevent reverse current. But diodes reduce voltage and waste a bit of power as a result.

The wall wart likely has a bridge rectifier internally and would not require an additional diode - you'd just need one on the battery. That would prevent charging.
 

Thread Starter

superway

Joined Oct 19, 2009
125
Are you hoping to charge the battery with the transformer? Does your load require a regulated voltage?

The simple way to OR power supplies together is to just put a diode on each one to prevent reverse current. But diodes reduce voltage and waste a bit of power as a result.

The wall wart likely has a bridge rectifier internally and would not require an additional diode - you'd just need one on the battery. That would prevent charging.
My Device Under test is drawn about 450mA when turning on. I don't think the wall wart is a good device for recharge battery, and it has very small wire( Awg#22) on output side, I rule out the charging. So can put a 1N4001 in series with postive cable on battery?
Thanks
 

Brownout

Joined Jan 10, 2012
2,390
An unregulated 12v wall wart can output nearly 17v. Make sure your device can tolerate the maximum output from your transformer. Otherwise, use a voltage regulator.
 

Thread Starter

superway

Joined Oct 19, 2009
125
When I used wall wart to power up 1 unit, the inrush current goes up to 1.1Adc about 3 sec., then drops down to 200mA. If I applied 2 units at the same time, the inrush current will be double while my wall wart is rated only 1000mA. Can it handle over current in 3 seconds?
Thanks
 

Thread Starter

superway

Joined Oct 19, 2009
125
3 seconds is a pretty long time. I assume you don't have any specs for you adapter, and so there is no way to know.
Yes, 3 seconds is a pretty long time to load about 2 amps, but after that the current drops down to 400mA. It is not good practice, but I just want to turn 2 units on for demo.

Thanks
 

Brownout

Joined Jan 10, 2012
2,390
Yes, 3 seconds is a pretty long time to load about 2 amps, but after that the current drops down to 400mA. It is not good practice, but I just want to turn 2 units on for demo.

Thanks
Its a bad idea, but if you already made up your mind you don't need my advice. Take care.
 

#12

Joined Nov 30, 2010
18,224
I don't think the adapter will survive 100% overload (for 3 seconds) more than a few times. Try it. If it smokes, you will know you were wrong and end up buying the right adapter.
 
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