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I have noticed with the large amount of optical drives and CD/DVD players I have taken apart that most of the spindle motors (RF-300, RF-310, RF-400, etc.) have the somewhat cryptic marking "D/V 5.9" on them along with the standard part number. This appears to be mainly found on spindle motors, and very rarely on the sled or eject motors. It also appears to be a fairly standard marking, as I have seen it on motors dating back to 1985. It could be the recommended voltage, although Mabuchi's information on the RF-300 says the voltage range is 1.5-6 volts and 3 volts is nominal. Some motors I have seen write "D/V" as if it were a fraction. All but 2 of the motors I have seen this on are made by Mabuchi, and on the ones that are not there is nothing after the "D/V" marking. I have been looking for an authoritative source on this for a while, and it seems there is none.

Any ideas about what it means or why it seems to be found only on spindle motors?

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  • \$\begingroup\$ My guess would be 'drive voltage' -- perhaps it's a maximum rating? I have seen some spindle motors that are D/V 13.0 which seems reasonable for a 12V DC system. \$\endgroup\$ – Krunal Desai Feb 23 '16 at 19:36
  • \$\begingroup\$ Why would it be 5.9 volts for a motor with a 6V maximum rating, especially when the manufacturer recommends 3V? \$\endgroup\$ – 3871968 Feb 23 '16 at 19:48
  • \$\begingroup\$ Additional info: some of the older motors I have seen this on write D/V as if it is a fraction. Could this mean something? \$\endgroup\$ – 3871968 Feb 23 '16 at 19:52
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    \$\begingroup\$ I believe this may have to do with the inertia of the rotor, which would be important in a device such as a disk drive were you must very accurately control the speed. \$\endgroup\$ – beeedy Feb 24 '16 at 20:03
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D/V most likely stands for disk varistor as Vicente Cunha suggested. Not only does the Mabuchi Motor website use the term D/V in this way, 5.9V and 13.0V also match up with two of the standard threshold voltages that TDK produce ring varistors for motors in, and these photos of another brand of CD spindle motor appear to show one of them soldered next to the commutator. (The black ring with solder pads around the outside. Apparently it needs to be on the armature to most effectively suppress noise, hence why companies like TDK offer specially-shaped varistors for this purpose.) So in short, D/V 5.9 probably means that it contains a varistor with a threshold voltage of at least 5.9 volts but possibly more due to manufacturing tolerances.

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  • \$\begingroup\$ Yes, that does appear to be inside the motors I took apart. \$\endgroup\$ – 3871968 Feb 26 '16 at 16:50
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I suspect D/V stands for "Disk Varistor". Where I got this hunch from. Disk varistors can be used as surge current protection. Perhaps the Mabuchi motors you've seen come with internal disk varistors. Prying one of them open should settle this.

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  • \$\begingroup\$ Time to take one apart. I'll try one of the unbranded RF-310s first. \$\endgroup\$ – 3871968 Feb 25 '16 at 19:29
  • \$\begingroup\$ I remember disassembling a spindle motor that had failed (one of the brushes had disintegrated) and I don't remember there being a varistor. \$\endgroup\$ – 3871968 Feb 25 '16 at 19:35
  • \$\begingroup\$ There are no varistors or other components of any kind in an unbranded RF-310 and in a Mabuchi RF-300. \$\endgroup\$ – 3871968 Feb 25 '16 at 20:43
  • \$\begingroup\$ Cold trail then. Another guess I had before this is that they could be specification of which brakes are compatible with the motor, like here - compatible with "Disk brake" or "V brake". But it's obviously not the case. \$\endgroup\$ – Vicente Cunha Feb 25 '16 at 20:47
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    \$\begingroup\$ This seems to suggest that the varistor in question may actually be a disk mounted to the motor shaft near the commutator, rather than an ordinary electronics component: precisionmicrodrives.com/tech-blog/2011/06/06/… \$\endgroup\$ – makomk Feb 25 '16 at 23:25
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I suspect it is the DC operating voltage. 5.9V appears to be a standard voltage for small DC motors. Example: Precision Microdrives 124-001 datasheet:

https://catalog.precisionmicrodrives.com/order-parts/product/124-001-24mm-dc-motor-12mm-type

Although the maximum voltage for this motor is 6V, the voltage for which all of the datasheet values are true is 5.9V.

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  • \$\begingroup\$ First of all, the website you linked to contains blatantly incorrect information (see "used extensively for cooling fans for PC and other computing applications"), so I am not sure I can trust the attached datasheet. Secondly, I have seen many datasheets, specification tables, and Amazon listings from manufacturers other than Mabuchi Motor say the drive voltage is 5.9, but Mabuchi has never listed 5.9V as a voltage for their motors or provided information on this marking. All but 2 of the motors I have seen this on are made by Mabuchi. \$\endgroup\$ – 3871968 Feb 25 '16 at 1:20

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