UPS makin weird noise

[andy]

i modified my UPS so itll last longer. i moved it from its existing case into a small computer case and added some fans (since it gerts hot enough runnin from just 1 battery).

the only changes to the UPS was a 70A relay to switch on the external battery when the power had failed, and to switch the fans on. it all works etc but the problem is, every 7-8 seconds it makes a noise for a second. it sounds like a large transformer under load. it gets fairly loud (compared to normal) then gets quite again. is this normal or should i be worried?

 

[toasty]

how are you charging the new bigger battery(s) if you are getting this noise when on mains AC, I suspect the bigger batteries (with correspondin lower internal impedence) are drawing more current from the charging circuit and perhaps overloading it?

I'm assuming we're referring to a cheap SOHO offline ups, and not an online device?

Cheers
-Dan

 

[andy]

how are you charging the new bigger battery(s) if you are getting this noise when on mains AC, I suspect the bigger batteries (with correspondin lower internal impedence) are drawing more current from the charging circuit and perhaps overloading it?

I'm assuming we're referring to a cheap SOHO offline ups, and not an online device?

Cheers
-Dan

the newer battery has its own charger. the relay is there to disconnect the external battery when there is no mains so it can be charged seperate from the internal battery. the UPS is a trust 800