Ground Power

[flyboy0681]

I have to connect ground power using this charger. How high on the AMPS can I go for about an hour?

[carusoam]

Let’s go with 50Amps is probably too high...

That would be like running the starter continuously for an hour...

or having your alternator charging at full output....

So technically, you might get away with it... if the cooling is adequate...

Since your hangar doesn’t have 150kt winds blowing through it in a nice organized fashion... pick the lesser numbers.

 

The 10amp number is typical for charging the battery in about an hour...

The 2amp number is typical of charging a battery overnight...

So 10 and two should be OK...

Compare that to how much current you are drawing out of the system...

Got a fancy current meter to go with that?

PP thoughts only, not an electronics guru...

Best regards,

-a-

 

 

[EricJ]

The notes imply that anything above 10 Amps has a duty cycle of five seconds on followed by 145 seconds off.   So continuous duty is likely limited to 10 Amps.

Those aren't very good for GPU duty.

[bradp]

Don’t use that for a GPU. It will cycle.  You need a continuous variable input power supply.  I use a 50lb transformer ham radio power supply that I use for running avionics. 
 

[A64Pilot]

If available a golf cart makes a good GPU, also makes a pretty good tug.

So far as a power supply, the bigger the better. So long as voltage is correct, a battery will only accept the current it can handle, That is why after starting the ammeter will show a high current but taper off as the battery is charged, hold a steady 14V and the battery acceptance eventually goes to zero.

Inexpensive chargers often will supply a voltage that’s higher than 14V. that’s why they can cook a battery if left connected too long.

[flyboy0681]

10 hours ago, bradp said:

Don’t use that for a GPU. It will cycle.  You need a continuous variable input power supply.  I use a 50lb transformer ham radio power supply that I use for running avionics. 
 

I'll run down to Radio Shack and get one today.

[MIm20c]

I would pick up a iota 12v 30 amp power supply if you’re going to be using it often. 

[N201MKTurbo]

Those chargers are not constant current, they are constant voltage. The different settings are just different taps on a transformer. They have SCRs or Triacs on the inputs that can switch the power on /off. When the voltage exceeds the threshold, they turn off, when the voltage gets below the threshold (with hysteresis) it turns back on. It does this so it doesn't over charge the battery. They are simple and effective battery chargers and are fine if you just want power for a database update or something like that.

[Warren]

A simple power supply that can set to a fixed voltage is perfect for this kind of work.  For a 12V system, set it to 13-13.5 V - 30A (20A would probably work reasonably well too) -- for a 24V system use 26-26.5V.  This is the maintenance voltage for the battery that a smart charger would maintain for the long term after charging is complete.  At this voltage, the battery will not receive significant charging and 30A should be lots to support what you need to run with the avionics while you are updating, training,... to avoid draining the battery.

[EricJ]

Here's a practical system from aircraft spruce that is actually a decent GPU, as long as you don't exceed the max current draw (which is reasonably generous).   I built my own and didn't spend a whole lot less than this costs, so it's not a bad deal.

https://www.aircraftspruce.com/catalog/elpages/portPowerCharger.php

[Danb]

8 hours ago, EricJ said:

Here's a practical system from aircraft spruce that is actually a decent GPU, as long as you don't exceed the max current draw (which is reasonably generous).   I built my own and didn't spend a whole lot less than this costs, so it's not a bad deal.

https://www.aircraftspruce.com/catalog/elpages/portPowerCharger.php

That’s what I use also, in addition I have a battery minder set up mainly for the electronic ignition.

[flyboy0681]

All good ideas here, but let me ask this. For a 12 volt system, what are the maximum amps that can be used for running it off GPU for an hour?

[A64Pilot]

33 minutes ago, flyboy0681 said:

All good ideas here, but let me ask this. For a 12 volt system, what are the maximum amps that can be used for running it off GPU for an hour?

Max amps is irrelevant, so long as voltage is correct the system will only draw what it can use. You can’t have too big of a charger, if it’s voltage is correct.

voltage is the “pressure” that pushes current into a  battery. too high a voltage will overcharge a battery, even at low amperage over time. 

Look at it this way, you have say a 70 amp alternator, but don’t use anywhere near 70 amps and can fly around forever and not overcharge the battery, that’s because the voltage is kept down to 14ish volts. If you had a 200 amp alternator it still won’t overcharge.

‘So a 125 amp battery charger will start out at high amps if a battery is low in charge, then as a battery charges the amps will decrease until a very low amperage when at full charge.

‘If your asking about that charger, 10 amps is it’s max continuous output. Your usage made exceed 10 amps, but that’s not a big deal as the battery will supply what’s needed over the 10, it will discharge of course, so charge it after your done.

‘I assume your charger does not automatically turn off, it has a timer off the picture, if so I’d charge the battery until the amp meter falls to about 1 amp then stop.

Edited June 4, 2021 by A64Pilot

[flyboy0681]

Just now, A64Pilot said:

Max amps is irrelevant, so long as voltage is correct the system will only draw what it can use. You can’t have too big of a charger, if it’s voltage is correct.

voltage is the “pressure” that pushes current into a  battery. too high a voltage will overcharge a battery, even at low amperage over time. 

Look at it this way, you have say a 70 amp alternator, but don’t use anywhere near 70 amps and can fly around forever and not overcharge the battery, that’s because the voltage is kept down to 14ish volts. If you had a 200 amp alternator it still won’t overcharge.

‘So a 125 amp battery charger will start out at high amps if a battery is low in charge, then as a battery charges the amps will decrease until a very low amperage when at full charge.

So many differing opinions here. One said that 50 amps was too much.

[A64Pilot]

2 minutes ago, flyboy0681 said:

So many differing opinions here. One said that 50 amps was too much.

No, I don’t believe so, I believe what he was saying was that charger can only provide 50 amps for 5 sec, then it will overheat and turn off.

the 50 amps setting is meant to get a low charge battery to start an engine.

Edited June 4, 2021 by A64Pilot

[A64Pilot]

What I believe your failing to understand is the the amp setting is not what the battery will accept, it’s the max output of the charger setting.

Try this, connect it to a fully charged battery. set it to 50, it won’t supply 50 because the battery won’t accept 50 because it’s fully charged, it wouldn’t accept even 10 after a few minutes

 

[EricJ]

7 minutes ago, flyboy0681 said:

So many differing opinions here. One said that 50 amps was too much.

The current load depends on what you have turned on or not.   Add up the circuit breaker values for everything that you want to have on at once when powered by the GPU and that's your maximum possible load.  The actual load should be much less than that since there is design margin before the breakers pop, but it will at least give you an upper limit.    From that perspective I would suspect that 50 amps is too much, as most of our airplanes don't have that much stuff to run at once, especially in the hangar, where you're not likely to have all the lights, gear, flaps, etc., running at the same time as whatever you're doing in the cockpit.

The one at aircraftspruce is 25 Amps, and I built mine for 30 Amps, and it's been fine.   25 Amps should be fine, but I suspect some people with a lot of glass panels, etc., nay be able to stress that pretty hard.

 

[Tom 4536]

1 hour ago, EricJ said:

The current load depends on what you have turned on or not.   Add up the circuit breaker values for everything that you want to have on at once when powered by the GPU and that's your maximum possible load.  The actual load should be much less than that since there is design margin before the breakers pop, but it will at least give you an upper limit.    From that perspective I would suspect that 50 amps is too much, as most of our airplanes don't have that much stuff to run at once, especially in the hangar, where you're not likely to have all the lights, gear, flaps, etc., running at the same time as whatever you're doing in the cockpit.

The one at aircraftspruce is 25 Amps, and I built mine for 30 Amps, and it's been fine.   25 Amps should be fine, but I suspect some people with a lot of glass panels, etc., nay be able to stress that pretty hard.

 

I have the Aircraft Spruce unit and a full glass panel. When the panel was new I would have the panel on 2-3 hrs at a time with no problem. The GPU has a fan and it does not get hot. The battery voltage was always 13+ volts when I was ready to shut off the panel.

[A64Pilot]

If using a 10 amp battery charger, I would not hook it to the external power plug myself. I’d hook it directly to the battery and use the battery to power my airplane and the charger to keep the battery charged, just as the alternator does inflight.

‘Very often anything but a high dollar power supply doesn’t really produce DC current, it’s AC rectified to pulsating DC, and the battery functions as a huge capacitor and provides DC current.

An alternator for example is not a source of DC current, it produces AC current that is rectified to pulsating DC through a diode bank, the battery functions as the big ole capacitor and provides DC current.

‘Then as was stated an RG-35AXC for example is a 33 AH battery, meaning it will supply 10 amps for 3.3 hours before being discharged fully, fully discharged is often 10.5 V.

So if you pull 10 amps. I’d be comfortable running the airplane for an hour or so, but recharge the battery as soon as your finished, but if you pull 10 amps and the charger can provide 10 amps, then with the charger hooked up, you can run it forever.

Edited June 4, 2021 by A64Pilot

[Will.iam]

My question about the spruce charger is that it’s only a 24v charger so how does it fully charge the battery if you need more than 24v to do it. Sure it will charge the battery to 24v but fully charged 24v battery is usually showing 26v resting after being on the battery minder charger. Isn’t that why the system is a 28v system and not 24v?  Same reference to 12v battery in a 14volt alternator system.  
seems like the spruce charger will keep from allowing the battery to be discharged below 24 or 12 if you are using that system but how does it fully charge the batter?

[EricJ]

8 minutes ago, Will.iam said:

My question about the spruce charger is that it’s only a 24v charger so how does it fully charge the battery if you need more than 24v to do it. Sure it will charge the battery to 24v but fully charged 24v battery is usually showing 26v resting after being on the battery minder charger. Isn’t that why the system is a 28v system and not 24v?  Same reference to 12v battery in a 14volt alternator system.  
seems like the spruce charger will keep from allowing the battery to be discharged below 24 or 12 if you are using that system but how does it fully charge the batter?

It's a charger for "24V" batteries, i.e., what you have if you have a 24V (aka 28V) system.

It is similar for 12V (aka 14V) systems.

[A64Pilot]

OK, many don’t understand and it’s an almost universal misunderstanding among pilots.Even the FAA examiner on my Commercial ride didn’t understand.

‘We have either a 14or a 28 volt system, but we have either a 12V or a 24V battery.

‘think of electricity like water, you have to have water at a higher level in order to get it to flow to another container. So you have to have a higher voltage to get electricity to flow to a battery to charge it, the higher the voltage if amps are unlimited, the faster the battery will charge, but too high a voltage and it will damage a battery, To charge a 12V battery most often a voltage of about 14.3 is about ideal. but battery construction may change it slightly, an Odyssey battery I believe wants 15 V or so.

‘So why do we fly around at 14V? The reason is 14V is a good compromise, it will charge a battery but more slowly than 14.3, but 14 isn’t high enough to really overcharge and damage a battery, so a simple “dumb” voltage regulator set at 14V is good enough, “smart” regulators do exist and their voltage set points are usually adjustable, they will charge at a higher voltage, then cut back to a lower “float or maintainer” voltage once the battery is charged.

A Battery minder does this, it charges at roughly 14.3V until either the current draw drops to a small amount indicating the battery is fully charged and the drops to 13.3V to maintain charge, if you left a battery at 14V permanently t would ruin the battery over time by drying it out, even an AGM. 

A fully charged battery at rest is just under 13V, and it’s considered “dead” at 10.5V

Double the above voltage numbers for a 28V system that has a 24V battery, that as you said shows 26V when fully charged.

‘People never used to worry about this stuff with just old factory instruments,but now we display things to .1 digits, they notice things are different than what they we’re always told.

If the Spruce charger is any good, I assure you it outputs slightly over 28V, it’s labeled a 24V charger in an attempt to not confuse people. Call it a 28V charger and lots of people would think they can’t use it because their battery is only 24V.

Edited June 4, 2021 by A64Pilot

[Will.iam]

15 minutes ago, EricJ said:

It's a charger for "24V" batteries, i.e., what you have if you have a 24V (aka 28V) system.

It is similar for 12V (aka 14V) systems.

Yep but if the charger only goes to 24v and a fully charged 24v battery is greater than 24v how do they claim it will fully change the battery? 
every charger i have shows a higher voltage output then the battery they charge. I. E. 6v charger outputs 7v 

8v charger 9v 12v charger 14v etc. this charger only puts out 12v or 24v so i don't see how it will “fully” charge the battery. 

[A64Pilot]

If it truly only outputs 24V, you are correct it will not fully charge a 24V battery, even a float / maintainer should output roughly 26.6 V or so.

On edit, you are just more observant than most, most have no idea what voltage there chargers produce

Edited June 4, 2021 by A64Pilot

[EricJ]

Just now, Will.iam said:

Yep but if the charger only goes to 24v and a fully charged 24v battery is greater than 24v how do they claim it will fully change the battery? 
every charger i have shows a higher voltage output then the battery they charge. I. E. 6v charger outputs 7v 

8v charger 9v 12v charger 14v etc. this charger only puts out 12v or 24v so i don't see how it will “fully” charge the battery. 

A 12V charger puts out about 14V.   A 24V charger puts out about 28V.

The spec sheet for the "24V" version says it cycles at 2.5V/cell, and a 24V battery has 12 cells, so actually 30V.

"12V" and "24V" are basically just the names for systems based on 12V and 24V batteries.   They typically run at 13.5-14V and 26-28V, respectively.

When you buy a "12V" voltage regulator, it typically regulates to about 14V.