Since maybe the 1950s lab grade time
equipment has used 24 volts DC as a power
The HP 5087A 24 Volt Backup power supply was used to power the 5060A
flying clock Cesium standards. The HP 100 series of instruments
all use 24 VDC power sources.
This particular unit came from eBay with a foam filled bag in
the battery space, like it has never been used.
Meter switch Output or Battery :0 - 40 Volt meter, -5, 0, +5 Amp meter
Fuse Failure lamps: AC, AC, OUT, Battery
Battery Charge lamp & Switch
Interrupt lamp & reset switch
AC Power Lamp
J1 - AC power connector 3 pins (cable connector =
- Black (hot) = pin A
- White (neutral) = pin B
- Ground = pin C
The power cable might be called a CX-3277
F1, F2 - Fuses
J2 - Alarm output 6 pin MS _______________
J3 - External Battery 4 sockets (cable connector = 97-3106B14S-2P
+ M85049/41-6A clamp)
J4 - Clock Out 4 sockets (cable connector = 97-3106A-10SL-3S)
(this is only a 24 volt
J5 - Oscillator Out 5 sockets 97-_____?? (this is only a 24 volt
J6, J7, J8, J9 - 24 Volt Outputs 4 Sockets (cable connector =
97-3106B14S-2P + M85049/41-6A clamp)
For those applications where a MS grade connector is not needed I'll be
using Power Pole
connectors in a 24 volt
Power Supply near Transformer
This PCB has a single multiturn pot and a fuse.
Power Supply with + Violet wire to battery
The PCB has two multiturn pots and a fuse.
The battery compartment has a clamping mechanism that will take up to
about 13.5 x 7.25" of batteries. This would hold 4 each 12 Volt
18 AH Gel cells like the TY-12-18. The quick connect connectors
are about 0.266" type, not the more common 0.187" type like on the
batteries, so if two batteries are used they need to be more like 40 Ah
types. The wire colors are +Violet and -Red (seems strange).
I'm using a couple of the very common 7AH 12 Volt Sealed Lead Acid
(SLA) batteries instead of the much larger batteries that the 1290 was
designed to hold. My concern is not long term power outage so
much as outages that last for a few seconds. These batteries are
not near as big so I'm looking at using a 1 foot long 2x4 as a rear
spacer so that the battery clamp can operate.
The quick fit terminals will need to be changed to the smaller 0.187"
type and a battery to battery jumper wire made up.
Looking from front of unit Ra to R3 left to right:
R1 regulated output bus on back panel when on AC 24.5
R2 battery charge v 26.46
R3 battery float v 25.43
The thing draws 21 VA when idle no batteries. Mostly due to the xformer.
Info thanks to Paul WB8TSL