[Amps] LDMOS amp off battery?

[Manfred Mornhinweg]

Steve,

> Is anyone running a 50V LDMOS amp off a 48V battery system?

I have considered it, but not done yet. I generate my own power, with a 
turbine in a creek, and in summer I can generate only about 400 to 700W, 
so I absolutely need batteries to run a legal limit amp.

But there are two choices: A local battery bank just for an amp, or 
using the main battery bank I have in place for the whole house - in 
that case the amp needs just its normal AC supply, and my DC-AC inverter 
takes care of the rest. That solution is cheaper to implement in my 
situation, but incurs in higher losses.

> I've been rolling this idea around for a while for portable use, but the
> problem is a "48V" battery system on equalise is more than a little bit
> more than 50V - more like 58V !
> 
> Any ideas?

First idea: Don't equalize the batteries while you are operating! During 
operation keep the charger regulated to 50V. The system voltage will 
then vary between about 48 and 50V as you operate, which should be OK. 
The batteries will lose charge, but will not go into deep discharge. 
After the operating session, raise the charge voltage to whatever is 
necessary for a complete charge, including equalization once every 
several months. Even if the voltage remains applied to the LDMOSFET, 
it's no problem while it's not being driven, since its maximum drain 
voltage rating is well over 100V.

And another idea: Use a battery bank of whatever voltage you like, 
either lower or higher but not 48V, run the batteries at their proper 
voltage, and use a switching regulator to produce a stable, clean 50V. 
Depending on the battery voltage that can be a buck or a boost circuit. 
It gives you the advantage of a stable, constant supply voltage, and if 
the battery voltage is reasonably close to 50V, then the size and weight 
and cost of the regulator is small.

Manfred

========================
Visit my hobby homepage!
http://ludens.cl
========================