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Re: [Amps] LDMOS amp off battery?

To: Manfred Mornhinweg <>,
Subject: Re: [Amps] LDMOS amp off battery?
From: Steve Wright <>
Date: Tue, 24 Oct 2017 09:34:46 +1300
List-post: <>
Hi Manfred,

I should have thought that you would have a unique perspective to add on
this topic!  When I travel the world on my yacht I shall come and see
you!  Maybe we could take a trip at sea and work DX and satellites /MM
all day?

On 24/10/17 06:49, Manfred Mornhinweg wrote:
> 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.

Yes, the house inverter is the easy way - just plug the amp in!  My
first paragraph lets the cat out of the bag - and space is a little tight!

> First idea: Don't equalize the batteries while you are operating!
> During operation keep the charger regulated to 50V. 

Yes, or switch in a couple of fat diodes in series to knock off a volt
or two.

The real question is, do I even need to do this?  Is 58V on the amp a
deal breaker?

> [...] 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.

So maybe the combination will survive..  Obviously drive levels will
vary..  Maybe I will have to add input ALC so it limits at 800 watts -
to avoid overdrive during high volts, and to avoid distortion at low volts.

> 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.

I thought about this too..  The yacht PV system charging (step up) from
24V (existing) to 50V, at levels well short of a kilowatt, and run a
smaller auxiliary 50V battery just for the amp.  This is a very simple
system, and is trivially separated from the yacht systems should things
get 'tight' - a very welcome thing to be able to do in an emergency.


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