Looking 4 a DC-DC converter

[Dave-s]

Input voltage 34-24v output 12v 3A.
I saw a few converters on eBay, but the input voltage range is not suitable. They are either 48v or 24v input.
My battery's top voltage is 33.6v, and I think this is too high for the 24v converters, and the pack low voltage cuttoff (24v) is too low for the 48v converters.

Advice please ...

 

[fechter]

This one should work:
http://www.allelectronics.com/make-a-store/item/PS-1233/12VDC-3.33A-SWITCHING-POWER-SUPPLY/-/1.html

See this thread on page 2 for a description: http://endless-sphere.com/forums/viewtopic.php?f=16&t=2264&p=55538#p55538

 

[Dave-s]

Thanks.
The question is how is their efficiency at these low input voltages?
Here's one for $10+$12 S/H: http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6256&Product_Name=12V_5A_Power_Supply
The DC-DCs on eBay are listed for $20 inc. shipping, and those have efficiency of > 90%.

Are these AC-DC really as good as DC-DCs?

 

[Dave-s]

And one for $12:
http://cgi.ebay.com/AC-Adapter-Power-Supply-for-LCD-monitor-TV-Cord-12V-5A_W0QQitemZ260377413127QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3c9fb40607&_trksid=p3286.c0.m14&_trkparms=66%3A2|65%3A15|39%3A1|240%3A1307|301%3A1|293%3A1|294%3A50

 

[frodus]

I've got one of those Vicor (only the 48V version), That was actually the one I was going to link to

they're nice because they're already wired up ready to go.

Upper end is 32V, but max is 36... you should be fine. Just fuse the input AND output. They're great converters.

 

[Dave-s]

Cant find the 24v Vicors on eBay.
According to the tests I saw on a different thread, using a AC-DC switching power supply as a DC-DC is much less efficient 79% compared to > 90%.
It's amazing how cheap you can get an AC-DC 12v5A P.S on eBay for. I cannot understand how parts+labor+shipping can be as low as $12.

 

[fechter]

I don't think the efficiency is a big issue as it is way better than a linear regulator. The power drain of your 12v load is very small compared to the motor in most cases.

The problem with AC power supplies is the lowest voltage they can operate at varies widely from model to model, so unless it has been tested, you won't know what the minimum input voltage is. Many of them won't work below 60v. The one from Allelectronics was tested.

 

[Dave-s]

But will the one from Allelectronics work down to 24v?

 

[fechter]

But will the one from Allelectronics work down to 24v?

Yes, It works down to 20v but the current may be a bit less than the rating.