I have a FL-760 radio. Before I fly I charge the battery for at least 6 hours (it's virtually brand new). Connected, it shows around 12.7 volts initially. When I transmit the voltage drops sometimes to around 11.4 volts. According to other pilots and ground crew my transmissions are initially clear but then fade to garble or screech. Reception is fine. Any thoughts?

On Monday, October 23, 2023 at 7:28:59 AM UTC-6, LoftusRoadLad wrote:
> I have a FL-760 radio. Before I fly I charge the battery for at least 6 hours (it's virtually brand new). Connected, it shows around 12.7 volts initially. When I transmit the voltage drops sometimes to around 11.4 volts. According to other pilots and ground crew my transmissions are initially clear but then fade to garble or screech. Reception is fine. Any thoughts?

Battery is junk. Replace.

On Monday, October 23, 2023 at 9:28:59 AM UTC-4, LoftusRoadLad wrote:
> I have a FL-760 radio. Before I fly I charge the battery for at least 6 hours (it's virtually brand new). Connected, it shows around 12.7 volts initially. When I transmit the voltage drops sometimes to around 11.4 volts. According to other pilots and ground crew my transmissions are initially clear but then fade to garble or screech. Reception is fine. Any thoughts?
What battery chemistry? Lead acid should be mid to high twelve volts charged, NiMH and others would likely be higher.
Low volts affect transmission.
How much use before transmission and degradation?

On Monday, October 23, 2023 at 9:28:59 AM UTC-4, LoftusRoadLad wrote:
> I have a FL-760 radio. Before I fly I charge the battery for at least 6 hours (it's virtually brand new). Connected, it shows around 12.7 volts initially. When I transmit the voltage drops sometimes to around 11.4 volts. According to other pilots and ground crew my transmissions are initially clear but then fade to garble or screech. Reception is fine. Any thoughts?

Consider replacing your battery with a Life battery. They are now very reasonable in cost and available from Amazon. Their charged voltage is about 13..8 volts and capacities are about 10ah.
UH

On Monday, October 23, 2023 at 1:20:41 PM UTC-4, Hank Nixon wrote:
> On Monday, October 23, 2023 at 9:28:59 AM UTC-4, LoftusRoadLad wrote:
> > I have a FL-760 radio. Before I fly I charge the battery for at least 6 hours (it's virtually brand new). Connected, it shows around 12.7 volts initially. When I transmit the voltage drops sometimes to around 11.4 volts. According to other pilots and ground crew my transmissions are initially clear but then fade to garble or screech. Reception is fine. Any thoughts?
> Consider replacing your battery with a Life battery. They are now very reasonable in cost and available from Amazon. Their charged voltage is about 13.8 volts and capacities are about 10ah.
> UH
You also might consider increasing the size of wire from your battery to the radio, which helps as well, particularly when you are transmitting.

Dan

On Monday, October 23, 2023 at 10:31:09 AM UTC-7, Dan Daly wrote:
> On Monday, October 23, 2023 at 1:20:41 PM UTC-4, Hank Nixon wrote:
> > On Monday, October 23, 2023 at 9:28:59 AM UTC-4, LoftusRoadLad wrote:
> > > I have a FL-760 radio. Before I fly I charge the battery for at least 6 hours (it's virtually brand new). Connected, it shows around 12.7 volts initially. When I transmit the voltage drops sometimes to around 11.4 volts.. According to other pilots and ground crew my transmissions are initially clear but then fade to garble or screech. Reception is fine. Any thoughts?
> > Consider replacing your battery with a Life battery. They are now very reasonable in cost and available from Amazon. Their charged voltage is about 13.8 volts and capacities are about 10ah.
> > UH
> You also might consider increasing the size of wire from your battery to the radio, which helps as well, particularly when you are transmitting.
>
> Dan
I had a customer that had that problem with a MicroAir 760. He was running it thru a 1 amp circuit breaker. Radios need at lease 4 amp breakers.
Also check that your ground is good.

Richard

If you are using a 12Volt Sealed Lead Acid (SLA) battery then the issues are that the fully charged voltage is only 12.7V and the output voltage steadily falls as the battery discharges. You might find that even a new SLA battery gives only 12.0V after 40% discharge. Some radios start struggling to transmit with under 11.5V.

I'd start by measuring the battery discharge rates with an ammeter whilst the radio is in receive mode and then transmit mode. If these are high, then look at what other equipment or faults is drawing current.

The most common size of glider battery seems to be 151 x 65 x 95mm. Lead Acid in this size is usually 7AmpHour. A similar size Lithium Iron Phosphate battery is available as 12 AmpHour, and is significantly lighter. Lithium batteries start at around 13.7V fully charged, drop quickly to around 13V where they remain for the majority of the time discharging before suddenly giving up useful output. These characteristics are ideal for gliding but there is a perceived safety risk due to the chemistry, especially if the battery is damaged. You need to check if lithium batteries are permitted by your country's sailplane regulator.
 
If you do run a lead acid battery, then you have to be very careful about 'voltage drop', which is the inefficient dissipation of power resulting in low voltage at the radio. Some tips have already been given but here's my thoughts:

- All cable has resistance. Minimise cable lengths and reduce the gauge (ie increase diameter). The cable from the battery to the main switch is usually the longest length of wire in the circuit and thus can be a major cause of voltage drop. It should be not less than 18 AWG diameter.
- The radio draws a high current so all components in radio circuit have bigger voltage drop. The radio should have its own dedicated sub-circuit ie dedicated CB/fuse. Most radio manufacturers say use minimum 18AWG tinned stranded copper to the radio.
- Minimise joints and connectors as these are a possible cause of high resistance ie voltage drop.
- If using screw connector blocks, use ferrules to avoid loose strands and ensure max contact with screw terminals.
- If a cable joint in the radio circuit is required, use crimps rather than solder.
- Circuit breakers have a high resistance, especially low Amp rated CBs. The smaller the CB rating the higher the voltage drop. Fuses have lower voltage drop.
- Check the condition of the master switch. A switch has internal resistance and thus voltage drop. This is usually very small but can be degraded by dust or moisture penetration, age or not up to the required DC amp specification.

On 24/10/2023 08:29, Bumpff Slam wrote:
> If you are using a 12Volt Sealed Lead Acid (SLA) battery then the issues are that the fully charged voltage is only 12.7V and the output voltage steadily falls as the battery discharges. You might find that even a new SLA battery gives only 12.0V after 40% discharge. Some radios start struggling to transmit with under 11.5V.
>
> I'd start by measuring the battery discharge rates with an ammeter whilst the radio is in receive mode and then transmit mode. If these are high, then look at what other equipment or faults is drawing current.
>
> The most common size of glider battery seems to be 151 x 65 x 95mm. Lead Acid in this size is usually 7AmpHour. A similar size Lithium Iron Phosphate battery is available as 12 AmpHour, and is significantly lighter. Lithium batteries start at around 13.7V fully charged, drop quickly to around 13V where they remain for the majority of the time discharging before suddenly giving up useful output. These characteristics are ideal for gliding but there is a perceived safety risk due to the chemistry, especially if the battery is damaged. You need to check if lithium batteries are permitted by your country's sailplane regulator.
>
> If you do run a lead acid battery, then you have to be very careful about 'voltage drop', which is the inefficient dissipation of power resulting in low voltage at the radio. Some tips have already been given but here's my thoughts:
>
> - All cable has resistance. Minimise cable lengths and reduce the gauge (ie increase diameter). The cable from the battery to the main switch is usually the longest length of wire in the circuit and thus can be a major cause of voltage drop. It should be not less than 18 AWG diameter.
> - The radio draws a high current so all components in radio circuit have bigger voltage drop. The radio should have its own dedicated sub-circuit ie dedicated CB/fuse. Most radio manufacturers say use minimum 18AWG tinned stranded copper to the radio.
> - Minimise joints and connectors as these are a possible cause of high resistance ie voltage drop.
> - If using screw connector blocks, use ferrules to avoid loose strands and ensure max contact with screw terminals.
> - If a cable joint in the radio circuit is required, use crimps rather than solder.
> - Circuit breakers have a high resistance, especially low Amp rated CBs. The smaller the CB rating the higher the voltage drop. Fuses have lower voltage drop.
> - Check the condition of the master switch. A switch has internal resistance and thus voltage drop. This is usually very small but can be degraded by dust or moisture penetration, age or not up to the required DC amp specification.
>
All true, but
On Monday, October 23, 2023 at 7:28:59 AM UTC-6, LoftusRoadLad wrote:
> I have a FL-760 radio. Before I fly I charge the battery for at least
6 hours (it's virtually brand new). Connected, it shows around 12.7
volts initially. When I transmit the voltage drops sometimes to around
11.4 volts. According to other pilots and ground crew my transmissions
are initially clear but then fade to garble or screech. Reception is
fine. Any thoughts?

Where are you measuring the voltage? At the Battery or at the Radio?

If you are measuring 11.4v at the battery, then the battery (or just
maybe, it's charger) must be suspect.

What chemistry is the battery?

On Monday, October 23, 2023 at 6:28:59 AM UTC-7, LoftusRoadLad wrote:
> I have a FL-760 radio. Before I fly I charge the battery for at least 6 hours (it's virtually brand new). Connected, it shows around 12.7 volts initially. When I transmit the voltage drops sometimes to around 11.4 volts. According to other pilots and ground crew my transmissions are initially clear but then fade to garble or screech. Reception is fine. Any thoughts?
Is this a change in behavior? Or is this a newly installed radio?
Eric

On 10/23/2023 1:20 PM, Hank Nixon wrote:
> On Monday, October 23, 2023 at 9:28:59 AM UTC-4, LoftusRoadLad wrote:
>> I have a FL-760 radio. Before I fly I charge the battery for at least 6 hours (it's virtually brand new). Connected, it shows around 12.7 volts initially. When I transmit the voltage drops sometimes to around 11.4 volts. According to other pilots and ground crew my transmissions are initially clear but then fade to garble or screech. Reception is fine. Any thoughts?
>
> Consider replacing your battery with a Life battery. They are now very reasonable in cost and available from Amazon. Their charged voltage is about 13.8 volts and capacities are about 10ah.
> UH

How old is the battery? Sealed lead-acid (SLA) batteries lose much of
their capacity after only 2 or 3 years. At least the cheaper ones.
Especially if deeply discharged in each use.

If/when it is time to replace this battery, listen to UH. LiFePO4
(LiFe, LFP) batteries are now no more expensive than SLAs (if you buy
cheaper brands), and are vastly superior. The cheapest ones (about $25)
are 6 AH (in the typical "brick" form factor, about 150x65x95 mm), which
may be plenty for your purpose, since they are OK to "fully" discharge.
The built-in protection will shut it down to prevent excessive
discharge. For a somewhat higher price you can get higher capacities
(8-10 AH) in the same physical size. Or 12-16 AH in the larger format
(about 150x95x95 mm) if you can fit that into your glider. Or use two
in parallel - if they are the same type and age, ideally same brand and
model, then it is OK to simply wire them in parallel, a switch is not
necessary.

On Monday, October 23, 2023 at 9:28:59 AM UTC-4, LoftusRoadLad wrote:
> I have a FL-760 radio. Before I fly I charge the battery for at least 6 hours (it's virtually brand new). Connected, it shows around 12.7 volts initially. When I transmit the voltage drops sometimes to around 11.4 volts. According to other pilots and ground crew my transmissions are initially clear but then fade to garble or screech. Reception is fine. Any thoughts?

Ok, so I hear it's a 9AH LifePo battery. Radio is good for about 2 hours.

My questions to OP....
What all is in the glider?
Transponder?
Radio (yes)
Flarm?
Electric vario?
Strobe?

The 2 hours, is that just "on time" or transmit time? If running a full panel but little transmit time, it's likely a failing battery, small wires, poor connections.

On Thursday, October 26, 2023 at 10:53:11 PM UTC-4, Charlie M. (UH, Pi & 002 owner/pilot) wrote:
> On Monday, October 23, 2023 at 9:28:59 AM UTC-4, LoftusRoadLad wrote:
> > I have a FL-760 radio. Before I fly I charge the battery for at least 6 hours (it's virtually brand new). Connected, it shows around 12.7 volts initially. When I transmit the voltage drops sometimes to around 11.4 volts. According to other pilots and ground crew my transmissions are initially clear but then fade to garble or screech. Reception is fine. Any thoughts?
> Ok, so I hear it's a 9AH LifePo battery. Radio is good for about 2 hours.
>
> My questions to OP....
> What all is in the glider?
> Transponder?
> Radio (yes)
> Flarm?
> Electric vario?
> Strobe?
>
> The 2 hours, is that just "on time" or transmit time? If running a full panel but little transmit time, it's likely a failing battery, small wires, poor connections.

Could be a ground loop.