Discussion in 'General Electronics Chat' started by 1-3-2-4, Feb 22, 2013.

1. ### 1-3-2-4 Thread Starter Senior Member

Dec 26, 2008
198
1
Besides radio shack does anyone know of a place that would have a 15v dc power adapter with a 1A output?

The one that RS sells is almost \$30 which seems a tad way over priced.

2. ### SPQR Member

Nov 4, 2011
379
49
Amazon!
It knows all, sees all and sells all!!!

3. ### gerty AAC Fanatic!

Aug 30, 2007
1,237
343
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4. ### 1-3-2-4 Thread Starter Senior Member

Dec 26, 2008
198
1
Maybe you can help me figure this out.. So I have a linksys 12V 1A power adapter.. it's unregulated and with no load I get 17.6 VDC when I put about a 1A load it goes to around 12.6 or so..

If I was going to put it on a load that was only 650 mA it's output voltage would be around 14.2-15?

first place I looked at was Amazon but was looking for some offered on prime.

Sep 7, 2009
2,498
510
6. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
510
You are better off just getting one that is regulated so the voltage doesn't vary so much.

7. ### SPQR Member

Nov 4, 2011
379
49
This is a fantastic question that I've always been confused about, and so reading a little, I've found the "KVL loop" explanation HERE.

Let's see if I do this right:

12.6 = 17.6 - (1 * X)
so X = 5

Vload = 17.6 - (.65 * 5)

Now let's wait to see if experts agree that (1) I've used the right formula and (2) I've used the right assumptions regarding Ro.

This is important enough for me that I might do another thread depending on their responses.
I wonder if this formula applies to switching power supplies.

Another great question!

8. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
510
The loading effect is typically not completely linear with load as there are several effects taking place.

9. ### 1-3-2-4 Thread Starter Senior Member

Dec 26, 2008
198
1
Well it will be regulated by the way of a LM317 any extra will be heat.. not sure how hot, but I'm building a SLA battery charger output voltage should be around 13.4 vdc @ 650 mA

10. ### 1-3-2-4 Thread Starter Senior Member

Dec 26, 2008
198
1
I have a question.. So I switched to a regulated supply that's 18.6V for the output anyways on the project I'm doing.. maybe it's because I ran the battery down to 11.5 V last night but it's been on charge for about 3 hours now and the LED is still lit, I assume it's charging rate is 650 mA but my battery voltage on the 12V 18 Ah battery is showing 13.05 volts.

How long does it normally take to fully charge it?

11. ### MrChips Moderator

Oct 2, 2009
17,776
5,547
An 18Ah battery could easily take 18h @ 1A.
Hence at 0.65A, expect at least 28 hours which is a lot more than 3 hours.

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12. ### 1-3-2-4 Thread Starter Senior Member

Dec 26, 2008
198
1

Thanks it seems to be working better with the correct input voltage now