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Re: [Amps] LDMOS amp off battery?

Subject: Re: [Amps] LDMOS amp off battery?
From: Manfred Mornhinweg <>
Date: Mon, 23 Oct 2017 17:49:02 +0000
List-post: <>

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.


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