BATTERY CHARGERS

[Highflight]

I SAW AN ARTICLE ON BATTERY CHARGERS. IS IT PERMISSABLE TO UTILIZE THE 2 AMP TRICKLE CHARGER OF A SEARS AUTO CHARGEWR ON A 12 V MOONEY BATTERY?

[stevesm20b]

Yes!

[rbridges]

as long as it has automatic shut-off

[231flyer]

Yes, but be careful not to leave on for more than 4 hrs at a time.  You are better off using a automotive float charger as rbridges suggests. Please see my post below on battery life:

Under "normal" operating conditions you should expect your Gill G35 to last 3-4 years in service.  The biggest variable to battery life is condition when asked to deliver cranking power and subsquent charge condition following startup. If your battery is fully charged before a start it will deliver a strong start (usually lasting less than 20 seconds) and need very little topping off by the ship's charging system (2-4 Amps) after startup.  If the battery is not fully charged, it will have to work harder to deliver the cranking power required.  After startup the battery will be relatively more depleted and will suck more Amps from the ship's charging system (could be 10 Amps if sufficiently discharged).  Large current draws tend to further heat up an already heated battery (normal chemical reaction when discharging or charging) and can result in warped plates and boiled off electrolyte.  A few cycles of this and you are assured premature battery death.  Its best to keep your battery "top off" charged with a float charger (max 2 amp rating if you are using an automotive type rather than one of the more expensive aircraft types which sense battery temperatures and can automatically vary the max current).  Flooded lead-acid batteries (G35 type) tend to be very hardy if maintained carefully.  In addition the electrolyte levels need to be monitored closely.  Each cell (6 in the G35) needs to be filled to the bottom of the filler split ring with distilled water on a regular basis.  In Texas my G35 will need a bit of water every 3-4 weeks. If the electrolyte level is too low the top of the plates will be exposed to air and will oxidize rapidly. Extreme temperatures do have an adverse effect on battery condition but can be minimized by pre-heating at temps below 40 degrees or parking the airplane in the shade in temps above 100 degrees. I use a battery minder and top-off charge my battery the night before a flight.

231flyer Full Member  Joined: Nov 04, 2011   Posts: 74 Location: Southlake TX United States

Re: Battery life Posted Apr 16, 2012 4:22 PM Rob: Your current charger should work fine if it can maintain currents at or below 2 Amps.  Just don't leave it plugged in for days on end. The cheaper float-types shut-off circuits have been known to malfunction ($4 Harbor Freight comes to mind). The float circuitry is very simple and highly dependent on the quality of electronics used. Its best to charge right before a flight so as to avoid any surprises.

[PTK]

I have the "Batteryminder Plug and run" aviation specific and leave it on all the time while in the hangar. Has served my battery extremely well and my alternator is thanking me I hope! Which brings me to a question I've always been wondering about. I know a full battery is good for the battery and for starting the engine, but once the engine is up and running does the alternator really care whether it is charging the battery or not? In other words is a full battery good for the alternator too because it doen't have to work as hard since the battery is full? Or it makes no difference to the alternator since its running anyway anytime the motor is running?

[Lionudakis]

I don't think the alternator life is effected much from actually pushing electrons or not. If the engine is running, the bearings are spinning, and the slip rings are rubbing, those are the physical parts that wear. If the battery is low and the alternator is working harder, heat is generated in the diodes and that takes a toll on them. I believe that is pure luck on how long those last.

[PTK]

[xftrplt]

...is a full battery good for the alternator too because it doen't have to work as hard since the battery is full? Or it makes no difference to the alternator since its running anyway anytime the motor is running?

Yes.  No.

The more power (amperage) an alternator produces, the greater the stress on its drivetrain, internal bearings, and the more heat it makes.  I suspect, as we've added fancier nav displays, engine monitors, etc., our alternators work harder, unless they've been upgraded.

Having a fully charged battery will demand less of the alternator(s), which can't be a bad thing--not to mention the safety aspect of having the nominal 30 minutes of electrical power in the event of the alternator failing. 

 

[PTK]

Quote: xftrplt

is a full battery good for the alternator too because it doen't have to work as hard since the battery is full? Or it makes no difference to the alternator since its running anyway anytime the motor is running?

Yes.  No.

The more power (amperage) an alternator produces, the greater the stress on its drivetrain, internal bearings, and the more heat it makes.  I suspect, as we've added fancier nav displays, engine monitors, etc., our alternators work harder, unless they've been upgraded.

Having a fully charged battery will demand less of the alternator(s), which can't be a bad thing--not to mention the safety aspect of having the nominal 30 minutes of electrical power in the event of the alternator failing. 

 

[1964-M20E]

Another method would be to use a timer on your charger and have it run for an hour each day minimal battery heating and will keep the battery fresh and this will work with any low amperage charger i.e. 2 to 4 amps.  This is of course if you are in a hanger where this is possible.  As for the power draw from the alternator you will probably not get that high in the range of the alt to make any real difference.  You could convert more of your lights interior and exterior to LEDs to reduce the power draw from the alternator and during emergency operations if necessary.

[xftrplt]

In other words to have max available amps is pointless since if the alt goes the amps are useless and you are really left only with the battery anyway?

Pete,

This time:  No and yes. 

The larger alternator is running at a smaller percentage of its rated output, thus not "working as hard," and less likely to fail (all other things being equal).  But, if it were to fail, all you've got are the amp-hours stored in your battery. 

[using a battery that won't hold a charge will lead to premature alternator failure, as it puts a continuous load on the alternator.  You might consider adding-up up your amperage draw at cruise and comparing that to your alternator's rated output.  (Though I haven't done this myself.)]

[PTK]

Dick, thanks. I'm sorry I'm a little confused or maybe I'm misunderstanding. Earlier you said the more amps the alternator produces the more stress on its drive train, bearings and more heat etc. Then you say the larger amps one actually works less percentage of time enabling it to last longer maybe. So its a good thing to have a higher amp one? Are you assuming on a fixed 30 amp needed current I used as an example? I've never done an amp tally either. I'm assuming with new state of the art electronics the amp draw should be less than it was before. I know with everything on except the landing light the needle on my ammeter barely budges from its zero center. With the landing light on its movement is noticeable.

[xftrplt]

I guess I'm not stating it well.  

For a given size alternator, the more amps, the more heat and wear.  (Think of regenerative braking.)  There's no free lunch in nature. 

For a given amp load, the larger the alternator, the lower its percent of rated power.  Sure, it produces the same heat for the same load, but it's engineered to higher specs to tolerate and/or shed the heat. 

[PTK]

Ok, so it is "better" to have a larger amp capacity alternator for a given amp draw. The alternator is more heavy duty plus, it will work less, right? A more rugged alternator working less can only be a good thing! This is not exactly why I thought of going to a greater amp value but it's ok by me! I was looking to have more amperage available to be able to run a portable ac unit for the summer season.

[jetdriven]

Many of these alternators are different amperage but the same deisgn.  IN the case of thr 201, you have the option of a Kelly reman 60A (prestolite, 1970 Ford), or a Plane Power 70A (nippondenso).  One of these recently ran 240K miles on my Eclipse.

How much is the amp draw anyway?  Im thinking 10 amps or less in cruise.  The landing gear motor of course has a high draw for a few seconds.

[xftrplt]

 

 

Maybe a bit higher, Byron.

A 530 pulls just under 4 amps @ 13.75VDC for GPS/Nav with Comm in receive mode and 10 amps when transmitting.

An Aspen PFD is 2.4 amps. 

Pitot heat is, I believe, ~ 10 amps.

Prop heat > 15 amps

 

 

[231flyer]

Battery draw is not a significant load for most alternators so its effect on alternator life is minimal.  Alternators are designed for a certain load factor which dictates the size and number of windings.  An alternator run at max capacity will run hotter than one at half capacity.  Heat will eventually breakdown the insulation in the windings (a type of varnish actually) and also affect the bearings and other electrical parts (diodes, connectors, brushes, etc).  Unfortunately we ask our airplane alternators to run under very harsh conditions.  The engine compartment is usually very hot and alternators are usually the recepient of a fine spray of engine oil.  Engine oil tends to collect acids and other corrosive compounds during normal operation (engine oil lubricates, cools, and scavenges waste combustion products). Unfortunately this oily mist can also cause premature alternator failure by corroding the insulation. The best way to prolong alternator life is to make sure the cooling shroud and duct-work is clear and properly installed. Next make sure the alternator is clean and not getting drenched in engine oil from leaks,sprays,mist, etc.  Finally manage the electrical loads well within the alternator max rating.  

Allsmiles, I am not sure of the type of ammeter in your bird, my 231 has a dumb ammeter that measures the current across a shunt in the battery circuit.  The needle mearly indicates if the battery is charging(+ve) or draining(-ve).  It does not measure the load placed on the alternator.  

My 231 came with a single alternator and vac pump.  Given their critical nature and having suffered from inflight failures of both I have made it a practice to replace them at 500 hrs in service regardless of condition.  Similar to magnetos, I find most manufacturers will design/manufacture to a 1000 hrs MTBF (mean time before failure) lifespan or better.  My Malibu Mirage has dual alternators and vac-pumps (automatic failover), I will run them to failure  and then replace/repair as necessary. 

[PTK]

Quote: 231flyer

Allsmiles, I am not sure of the type of ammeter in your bird, my 231 has a dumb ammeter that measures the current across a shunt in the battery circuit.  The needle mearly indicates if the battery is charging(+ve) or draining(-ve).  It does not measure the load placed on the alternator.  

My 231 came with a single alternator and vac pump.  Given their critical nature and having suffered from inflight failures of both I have made it a practice to replace them at 500 hrs in service regardless of condition.  Similar to magnetos, I find most manufacturers will design/manufacture to a 1000 hrs MTBF (mean time before failure) lifespan or better.  My Malibu Mirage has dual alternators and vac-pumps (automatic failover), I will run them to failure  and then replace/repair as necessary. 

 

[1964-M20E]

Quote: allsmiles

Is there a way to actually measure amp load at any given moment? Isn't this useful info to have? Or I guess knowing the actual value is of no consequence as long it's well within the alternator capability, right? It seems we have voltage info (I have 3 instruments to get volts from) and battery charge status but nowhere do we see a display of amp load! 

 

[Awful_Charlie]

If you have a seperate alternator switch, you can get a quick indication of the draw by taking it offline for a few seconds (or even minutes if you are confident about your battery) - remember that everything you take out of the battery is going to need to be put back though

I expect you could also do this with the circuit breakers, but you need to understand your system well enough that you don't fry the rectifier or regulator - maybe a job to do on the ground with everything running and your A&P in the RHS

[231flyer]

Alternator load is a very useful measure and newer a/c tend to come installed (my Malibu Mirage has an ammeter for each alternator).  In order to get an accurate reading you would install an appropriate shunt (70A for a 70A rated alternator) and then measure the current across the shunt in the alternator circuit.  Its a simple operation and could be done on a one-time basis with a multimeter or permanently.  

I would not recommend taking your alternator offline inflight if you have a single alternator system in your bird.  Although the battery can probably handle the load momentarily, it can drop charge precipitously if you overload the battery capacity (the Gill G35 is a modest 17 Ahr battery).  The alternator field coil requires alteast 2 amps to excite the circuit and cause the alternator to produce charge. If the battery dies while load testing, the alternator may fail to come back online. This is the reason mechanics will recommend you actually charge a dead battery rather than jump start and go. If unable to charge and a jump start is the only option, you should always plan extra ground run time so the battery can recharge some standby power to keep the alternator going. Its a common misconception that our alternators are totally independent. 

[jetdriven]

You can pull and reset the ALT FIELD circuit breaker with the engine running.  In fact, the POH says to reset this breaker if the alternator goes offline. 

[231flyer]

The alternator field coil needs external power to excite the circuit.  If the battery is dead, resetting the field CB will have no effect in bringing back the alternator online.  Try this, disconnect your battery and get a jump start (safer than starting and then disconnecting the battery).  Now take the alternator offline by pulling the alt field CB. Although the engine is running, restting the ALT Field CB will not bring the alternator back online. The field circuit needs some source of external power. The POH advises to reset the field CB assuming the battery in online and has some reserve capacity.