Yaesu: Yaesu FT-991 Off-State Current Draw

[rfrose]

Equipment Used​

• Regulated 13.8 V DC power supply (Siglent SPD3303X-E certified)
• Calibrated digital ammeter (series measurement), accuracy ±1.2% or better in the auto range. (Mastech MS8340A)
• Short, low-resistance test leads.
  Stable ambient temperature (72 deg. F.)
  
  

Test Configuration​

• Transceiver connected to the 13.8 V supply through the ammeter in series with the positive lead
• Negative lead returned directly to the supply
• No accessories connected (no tuner, no USB, no external devices)

Radio allowed to sit powered but OFF for several days before measurement to allow any internal circuits to stabilize.​

Measurement Procedure​

1. Verified supply voltage at the radio power connector was 13.8 V ±0.05 V under no-load conditions.
2. Inserted the ammeter in series with the positive DC lead.
3. Confirmed normal receive current with the radio ON to verify correct meter polarity and wiring.
4. Powered the radio OFF using the front-panel power switch.
5. Allowed the radio to remain in the OFF state for several minutes.
6. Recorded steady-state current draw once readings stabilized.

Repeated the measurement multiple times to confirm consistency.

Results​

• Measured off-state current draw:
  14.4 mA ±0.1%

The reading was stable and repeatable, with no observable decay toward zero over time.

Notes and Interpretation​

• This indicates the FT-991 does draw a small but continuous standby current when the front-panel power switch is OFF.
• The power switch does not fully disconnect the radio from the DC supply; internal circuits remain powered.
• This standby current is significant for:
  • Battery-powered installations
  • Mobile installations
  • Long-term storage without a master power disconnect

At 14.4 mA, the radio will draw approximately:

• 0.35 Ah per day
• ~10.5 Ah per month

 

[MTS2000des]

This is the case with just about every modern transceiver that uses a "soft power off" design. Obviously some circuitry must be kept alive. All LMR radios on my bench I support for work (Motorola APX4500, 6500, 7500 and 8500) draw about the same 10-15ma of current in "deep sleep". Any mobile installation of any such radio where a vehicle will be long term stored (more than a week) without being run, an installer should put a cut off device or circuit breaker inline. This is what we do on all our installations to prevent battery drain from radios, lights, etc.