Low battery charge

[rapidshot]

Does it have any influnce on the operations of radio and transponder in the early stages of the flight, if so how, thank you

[Mark 1]

Older radios are more likely to be sensitive to low bus voltage; modern ones with switched-mode(?) power supplies less so.

It depends on the reason for the low SOC on the battery. If it's extended ground use of electrical equipment without the engine running, then the alternator should bring things back to a healthy state very quickly.

A knackered battery or faulty regulator/alternator may give problems.

[Winhern]

If the battery had enough life to start the engine, then it'll likely have enough capacity to power the radios. And a serviceable alternator should be able to power the radios in that case no problem.

[rapidshot]

As you know it has been sometimes an headache to start hot engines,

After several attempts to start the engine , eventually throttle wide open, rotating the prop in opposite direction i could start it and i found myself flying with efis display turned into black and white screen, transponder not operating , all for a while , may be 5 to 10 minutes,then everything turned into normal conditions,

One other time engine started normaly but i could not receive any messages from tower at the holding point which reminds me low current/ voltage, that was a busy international airport , thanks to hand helds by the way

That was the reason why i asked the questions, i am about to come to a decision to change my battery which is new with another brand,

Thanks to all who have shared their opinions,

[Jan Olieslagers]

I must second Winhern's opinion: a battery that is able to start the engine in less than absolutely perfect conditions must be considered OK.

[Big Pistons Forever]

Batteries should not be looked at in isolation. They are half of the electrical system the other half is the alternator (or generator in older planes). You can get a good start from a fully charged battery but if the charging system is not on line you are quickly going to run out of power as its charge is depleted.

That is why checking the ammeter is an important after start, preflight, and in flight check.

If the charging system fails in flight the battery will be supplying all the electrical loads. As it is depleted the voltage will drop. The first thing to go will be the transponder as it needs full voltage, so if you are flying along and ATC suddenly says that they are no longer seeing your transponder return one thing to consider is that this might be the first sign of electrical problems. Of course as soon as the charging system goes off line the ammeter will show a discharge so if you regularly scan the instruments you should pick up the problem early.

As the previous poster me mentioned, if you deplete the battery starting the engine the radios will not work at idle power because the battery doesn't have enough volts but the RPM is too low for the alternator to provide the power. If you get stuck in this position increasing the RPM to 1500 should provide enough juice to get the radio on line. This however is not a great practice.

If I get a start off a weak battery I always stay at idle and watch the ammeter. It should show an initial high rate of charge which after a few minutes should start to reduce. If the charge rate stays very high then you have battery and/or charging issues and you should get an engineer to look at the aircraft .:(

[Winhern]

Hmm. The op reports the problem occurring in the air, when presumably the engine was running well above 1500rpm. The problem also has affected at least two flights with a lot of churn to start a hot engine - if the alternator was knackered then I suspect the battery would be flat by now. I wonder if the master switch operates a mechanical relay which is sticking?

[Mark 1]

Alternators can sometimes lose one phase or set of windings giving symptoms of lower output voltage and failing to keep the battery fully charged, though still enough for the basics.

A check on the system voltage when problems occur may narrow down the options.

[peterh337]

a battery that is able to start the engine in less than absolutely perfect conditions must be considered OK.

It is not so that a battery which starts OK is a good battery.

All that proves is that its internal resistance is low enough and that it holds enough charge for the starting.

The battery capacity could be 1/3 of the new capacity.

I've just replaced a £400 Concorde battery, after 6 years, due to this. It "worked" just fine.

If I get a start off a weak battery I always stay at idle and watch the ammeter. It should show an initial high rate of charge which after a few minutes should start to reduce. If the charge rate stays very high then you have battery and/or charging issues:ok:

[jxk]

It's not mentioned how old the aircraft is or whether it is kept inside or out but one thing to check is that all terminals especially around the battery, master and starter relays are making good contact. If the engine has been removed check that the 'earth' wire has been correctly reinstalled.

[Ringway Flyer]

Worth mentioning that it's good practice to have radios OFF before starting and shutting down. Nasty voltage spikes can upset radios/transponders and cause odd things to happen.

I know that modern equipment should be immune to such things, but better to be cautious?

RF

[peterh337]

I think starting is the bad one, with starter motor transients on the bus.

I have never found an explanation of why shutting down should be a problem, provided the voltage regulator doesn't have some bizzare fault.

[rapidshot]

It's not mentioned how old the aircraft is or whether it is kept inside or out...

it is 2008 model and kept in closed hangar, an evektor with around 300 hours flight time,

[david viewing]

My plane has flown little in the last 6 weeks and not at all in June until yesterday. The 'low volts' light stayed on (flashing at a low rate) during circuits and only extinguished completely after 40 mins flying. (Ammeter normal).

Does anyone know why the light would flash at a consistent rate (about once per second)? I thought 'strobes' but it wasn't that. What voltage do these low voltage lights come in/go out at?

[cockney steve]

possibly a voltage-sensitive Relay,....volts rise, relay connects load, volts drain down , relay drops out......repeat until throttle is opened enough that the output of the alty equals the load on the system.

drive-belt must be tight-enough to transmit load.....the standard Vee-belt is designed to "wedge" into the pulley-groove. If it's too loose, it'll slip until the rubber gets warm amd sticky enough to grip and "clutch-in".

Ever started your car ona frosty morning and heard the deafening squeal,varying every time you blip the throttle, then it magically disappears?

answer as above and also, having just depleted the battery with the starter-motor, the alty is trying to shovel about 50 amps back in...the alty acts as a big brake , absorbing 1-3 horsepower to generate that current...that's why a loose belt protests.

[Winhern]

Quote:
a battery that is able to start the engine in less than absolutely perfect conditions must be considered OK.
It is not so that a battery which starts OK is a good battery.

All that proves is that its internal resistance is low enough and that it holds enough charge for the starting.

The battery capacity could be 1/3 of the new capacity.

What we're trying to say is that if the battery has enough deliverable charge to turn the engine over normally, then PROB99 the electrical system is going to be able to power the radios when they are switched on a few seconds later :)

[Big Pistons Forever]

What we're trying to say is that if the battery has enough deliverable charge to turn the engine over normally, then PROB99 the electrical system is going to be able to power the radios when they are switched on a few seconds later :)

I would suggest a more correct statement is that if the that if the battery has enough deliverable charge to turn the engine over normally, then PROB99 the Battery is going to be able to power the radios when they are switched on a few seconds later. The ammeter must still be watched to see if the electrical system is charging and that may take an increase in RPM to get the alternator on line.

If the battery is not being charged then while it may initially power the radios obviously it will eventually lose enough power that it will no longer run the radios.

Note: For Generator equipped aircraft the gen fail light will be on below about 1100 or 1200 RPM so you generally will not be able to prove the charging system before the runup.

[david viewing]

Slight thread drift, but there's more to this with some cars. S-Type Jag started giving strange electrical problems. Started just fine, but a full house of warning lights, dropping into limp home, etc. "Strange electrical problems = change the battery" it said on the internet.

Hmmm, suspicious as ever, but I swapped the battery for a new branded Varta one on a Defender. The 8 yr old original fit Jag battery started the Defender perfectly. But the new Defender battery on the Jag = christmas tree lights on dash.

Oh I thought it's another harness problem. Off to the dealer. "It's the battery" they said, look at the printout, it drops below some threshold on starting. So I had two dud batteries, both of which could start a diesel Defender perfectly. In desperation I told the dealer to fit a new branded Jag battery, but it had better fix the problem. It did.

The old batteries are still providing good service, one on a Defender and the other a Fordson Major.

Oh and the plane? Ran perfectly yesterday. Battery must have recovered (I've convinced myself).