• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

SLA Battery (Filament Supply) DC Reference limits?

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Ludwig Haus

Disabled Account
2015-06-14 5:44 am
It varies
Hi,

I'd like to ask if anyone has information regarding how safe it is to reference a SLA battery (filament supply) to a 250V supply?. I've ran them before referenced to 100V or so, but this new design is more than double that and I cant find any info out there.

Any replies much appreciated.

L.H/S
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
The safety risk is simply that the battery is at whatever voltage you are floating it on. In practice that means the battery should be in an insulated area of the unit and inaccessible to prying fingers. There is also the real possibility of slight electrolyte seepage from the terminals and possibly vents (it can happen even on SLA's) and that could make the whole battery case conductive.

So I would say for total safety that the battery must live on a plastic tray and that the no part of the battery case must contact anything conductive. There must also be no possibility of anyone being able to access the battery unaware that it is all at high potential.
 
L.H/S what are you actually proposing?

Is the 250V supply a secondary side DC supply referenced to safety ground?

How are you going to maintain the battery at nominal full SOC and moderate temperature, and avoid a deep discharge?

I assume you are aiming at using a small 2-7Ah 6V monobloc. They present a risk from electrolyte leakage and explosion if not managed properly.

Ciao, Tim
 

Ludwig Haus

Disabled Account
2015-06-14 5:44 am
It varies
L.H/S what are you actually proposing?

Is the 250V supply a secondary side DC supply referenced to safety ground?

How are you going to maintain the battery at nominal full SOC and moderate temperature, and avoid a deep discharge?

I assume you are aiming at using a small 2-7Ah 6V monobloc. They present a risk from electrolyte leakage and explosion if not managed properly.

Ciao, Tim

Thanks for the replies.

250V supply is B supply of the amplifier and is referenced to safety ground, yes. 12V 6Ah SLA to power 250mA 5V filament with series rheostat and choke between the -225V node in the schematic and the filament return of the tube.

I had something similar but at 100V for a couple years and it worked ok, but not wanting to push things without knowing the risks (and I dont know).

Otherwise, I can always look to a CCS based regulator which can be safely referenced to the B supply..

Thanks,

L.H/S
 

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