Hi, I've seen this done before on low current designs. Sometimes when you replace the batteries in this type of design the circuit voltage does not have time to drop completely away due to the charge saved on bulk capacitors. When the new batteries are added the circuit comes up in a peculiar state. This is particularly true of uP power on reset circuits. There are more elegant ways to take care of this problem but I suppose a single resistor would be the cheapest (if one ignored battery life).
Regards, Kevin Harris Manager, Approval Services Digital Security Controls -----Original Message----- From: Maxwell, Chris [mailto:[email protected]] Sent: Monday, September 25, 2000 11:31 AM To: 'EMC-PSTC Internet Forum' Subject: Battery Safety All, We have inherited a design from a company which we purchased. The product is a handheld and can be operated from a pair of Alkaline batteries. Inside the unit, there is a 91 KOhm resistor across the + and - terminals of the batteries. Since the people who designed the instrument are long gone, some of my collegues have asked me if this resistor could be a safety feature. I can't think of any way this resistor would help the safety of the instrument. I did read through the safety test report; and I found no reference to this resistor being required. All it does is provide a constant drain on the battery (reducing battery life). It has been suggested to me that some designers put resistors across batteries to reduce the electrical noise in a product. To me a capacitor would be better for this because it wouldn't drain the battery while it was filtering. Even so, isn't a battery the ultimate capacitor? I'm just drawing a blank why anyone would do this. I'd love to recommend that we pull this resistor out because it's a pain to solder and it affects battery life. However, I don't want to sacrifice the safety of the product. Anybody want to take a guess at this one? Thanks. Chris Maxwell, Design Engineer GN Nettest Optical Division 6 Rhoads Drive, Building 4 Utica, NY 13502 PH: 315-797-4449 FAX: 315-797-8024 EMAIL: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
