Pat wrote:

Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

This sounds perfectly normal. I presume it is a switching power supply,
and needs capacitors to buffer the switching pulses. So, the capacitor
draws a large current at turn-on. You may need a high current relay
to handle the turn-on surge without damage. Yes, your unit apparently
needs a small load to continue regulating properly. Definitely
put a fuse in the 48 V input to it.

Jon