On 07/01/10 11:10, Steve Fosdick wrote:
In a modern unit I would expect both the converters to be switch mode designs and, from what I remember, one of the difficulties of switch mode PSU design is that one generally wants the control electronics powered from the low voltage DC which isn't available until the unit has started up thus necessitating some extra components for a "startup mode". My guess is that in the case of those cheap UPSs they miss out the extra components and use the battery to power the control electronics until the input SMPS has got going in which case if the battery is dead it won't start.
Interesting...
The implication of this is that if I charge the battery outside the unit then I can recover the unit.
Alternatively, if I can provide the necessary DC supply to the control electronics then the UPS may recover itself.
Any hints as to whether this can be done and/or how? I appreciate, by the way, that the whole point of a UPS is that there are high voltages kicking around, so this is a completely theoretical interest and I won't blame anyone if I subsequently kill myself...