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 How to Choose a GPU

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 BatteryMINDer Built-In
            Advantages of a built-in
       battery maintenance charger
                  and maintainer

Frequently Asked Questions

GPU Questions

Download your manual here.

Q: Which GPU is right for my aircraft?

See our complete guidelines here. Ideal for most certified aircraft, our 24 / 28-volt GPUs come in 27, 50, and 70 amp versions. The 27 amp models are adequate for most piston singles and twins for powering cockpit electronics and airframe systems. For more complex aircraft, and for powering high current systems like hydraulic motors and environmental systems, the 50 and 70-amp models are more appropriate. For commercial aircraft maintenance facilities, we recommend the 70-amp unit. For experimental or amateur-built aircraft which usually have 12 / 14-volt airframes, we offer 35 amp GPUs with several different connector options.

Q: Does the GPU have a battery?
No, the GPU is a power supply and power conditioner that converts AC power to DC for the airframe. It must be connected to an AC outlet to function, preferably a dedicated circuit.

Q: What causes the GPU to stop working (overload, protection or shutdown)?
A: Connecting a GPU, any GPU, to some aircraft may automatically energize certain airframe systems (like motors for air conditioning or hydraulics) that could cause an overload condition. A sustained overload will cause the GPU to self-protect and shut down. To restore GPU operation, disconnect it from the aircraft and cycle the power switch to reset its internal protection. To prevent the overload condition, identify and pull the circuit breakers that control those devices, then reconnect the GPU.

Q: Does the type of aircraft battery make any difference when using a GPU?
While a fully charged battery of any chemistry may be safely used in-circuit with a GPU, a discharged battery should always be removed from the aircraft for bench charging. An overload may be encountered if a partially discharged battery is used in-circuit with the GPU’s output. In this case, the GPU’s response to the battery may exceed either its maximum charging rate and voltage, or the GPU’s capability, causing an overload protective shutdown. It is the aircraft owner’s responsibility to follow the battery manufacturer’s instructions for charging and capacity testing the battery for airworthiness before reinstalling and/or using it in-circuit with a GPU.

Q: Is your GPU compatible with aircraft equipped with glass cockpits?
A: Yes. Our GPU precisely replicates the in-flight electrical environment, supplying a steady, noise-free 28-volts DC to the aircraft’s main electrical bus, all the way up to its rated output. It is compatible with all types of aircraft electronics and instruments, including those where flat screen displays and computers replace conventional instruments and gyros.

Q: Can I use your GPU to start my aircraft engine?
A: Generally no. Our GPU models are designed to power the avionics and airframe electrical systems in general aviation piston aircraft, and light turbine aircraft. The 70-amp GPU is adequate to provide start assist only for piston engines up to 600 CID. Our GPUs are not designed to assist, motor, or start any turbine aircraft engine. A more complete discussion of this is in the GPU manual, available to download.

Q: Can the GPU be used to “top-off” my aircraft battery’s charge?
A: Yes. In most aircraft, the ship’s battery can be added to the external power circuit so that it is inline with the GPU’s 28-volt output. This will effectively charge the battery, just as it would in flight. However, the GPU is not an automatic battery charger. It has no way to monitor the battery’s state-of-charge, or compensate for non-standard ambient temperatures. Therefore, it should not be used for long term charging or to charge a severely discharged battery, one with a static voltage of less than 22. Severely discharged batteries should be removed from the aircraft for proper servicing and tested for 85% of their rated capacity. Download the GPU manual for a more complete discussion.

Q: Is a standard 15-amp grounded wall outlet sufficient to power the GPU?
A: Yes, for the 27 and 35-amp GPU. For the 70-amp GPU an AC input limited to 15-amps will not allow it to produce its full output. It will be limited to about 50 amps. We recommend a 20-amp dedicated circuit for our 50 and 70-amp GPUs to realize their full potential. Most situations require an extension cord. Use a 12-guage HD cord of the shortest length possible to deliver maximum input power to the GPU.

Q: What sort of electrical protection is designed into your GPU?
A: Our internal switching-mode power modules feature overload and short circuit protection. Additionally, our dual digital power meter circuit also monitors the GPU’s output and will warn of any overload condition by flashing the display and sounding an audible alarm whenever the rated output is exceeded. If a significant overload condition persists, the GPU will automatically shutdown to protect the aircraft and itself – OL will be displayed on the meter. GPU operation is restored by disconnecting it from the aircraft and from the AC input.

Q: Do the GPUs with internal BatteryMINDer work outside North America?

A: The GPU itself may be used with almost any voltage, but the internal BatteryMINDer is only compatible with a 100-127V AC power source. In countries with other voltage standards, a compatible BatteryMINDer must be purchased and used separately.

Q: Is the GPU BatteryMINDer compatible with Concorde batteries? 
A:  Yes, BatteryMINDer chargers inside our Ground Power Units do not require any special configuration to properly charge Concorde batteries.

Q: Why does Audio Authority sell aviation products?

A: Audio Authority was the original designer and manufacturer of ground power products sold by Enhanced Flight Group, LLC. After Enhanced Flight ceased operations in 2009, demand was still strong for these products, so they are now available directly from Audio Authority and also from our distributors, Sporty's Pilot Shop and Aircraft Spruce. 

BatteryMINDer and Harness Questions

Q: Do you have instructions for installing a BatteryMINDer quick-connect in my airframe?
A: The instructions that come with our BM-AIK Airframe Interface Kit are generic and will guide the installation on most any aircraft (see this video tutorial as well). However, we also have a growing collection of downloadable installation examples with specific suggestions and photographs showing how our kit has been installed on many popular aircraft. Check the list to see if your aircraft is covered. If it is not, we would be interested in working with you to design an installation and get your photographs to create an example document for others in the future. Contact us for details.

Q: Can I leave the BatteryMINDer connected for long periods of time?
A: Yes, the BatteryMINDer is designed to remain connected to your aircraft whenever it is not flying for continuous maintenance and desulfation. It will not overcharge or damage your battery.

Q: My mechanic or aircraft manufacturer claims installing the BM-AIK2A is a major alteration and would require an STC. Is that true?
A: No, the FAA is the sole governing authority on modifications of certified aircraft. The BM-AIK kits have been reviewed by FAA and industry personnel, who agree that its installation does not rise to the level of a major alteration to the aircraft. Only a major alteration, as defined by federal aviation regulations, requires an STC, or FSDO field approval, and filing an FAA form 337 to document the change. It is not the decision of the airframe manufacturer, or type certificate holder. Because it is NOT a major alteration, it is a MINOR alteration, which is within the authority of the installing mechanic to sign off with a simple maintenance log entry.  If a mechanic is hesitant about his legal authority to do this, consider looking for one who understands their FAA designated authority.

Q: Can I build my own quick-connect battery harness for full-time maintenance charging?
A: For experimental aircraft, the answer is yes. For certified aircraft, there are basically two requirements to be legal. The materials from which the harness is fabricated must be aviation grade, conforming to some recognized quality standard, such as military specifications. The installation on a certified aircraft also requires approval. So long as the installation remains within the FAA’s definition of a minor alteration, any licensed mechanic has the authority to fabricate, install, and approve the installation for return-to-service with a airframe maintenance logbook entry. Our Model BM-AIK2A provides a convenient kit of aviation parts from which your mechanic can easily fabricate, install and approve a charger connection. Watch the video tutorial and see this supplemental tip to assemble the fuse holder.

Q: My aircraft has two batteries. Can I use one BatteryMINDer to maintain both of them?
A: Technically, yes. However, there are some limitations. Both batteries must be of similar age and condition. However, when connected to more than one battery, the charger cannot determine the individual condition of each battery so the built-in diagnostics of the charger are compromised. See the BatteryMINDer manual for specific details, requirements, and limitations of charging multiple batteries. Generally, better results are obtained by having each battery served by its own charger and that is what we recommend.

Q: Is there any difference between the BatteryMINDer that you offer inside your GPU and one that is sold separately?
A: No, it is electrically and functionally the same. We partner with VDC Electronics, manufacturer of the BatteryMINDer to offer this option as a convenience. It is identical to the aviation-specific Models 24041-AA-S2 or S5. We simply install their circuitry into our metal case and adapt the battery connection to the SB50 aviation connector. The BatteryMINDer’s ambient temperature sensor is integrated into our output cable.

Q: Is the GPU BatteryMINDer compatible with Concorde batteries? 
A:  Yes, BatteryMINDer chargers inside our Ground Power Units do not require any special configuration to properly charge Concorde batteries.

Q: Does the BatteryMINDer work with NiCad or Lithium batteries?
A: No, the BatteryMINDer must only be used with lead-acid batteries.

Q: Is your BatteryMINDer quick-connect compatible with all chargers? 
A: No. The BM-AIK2A wire guages and fuse are designed for chargers that output 8A or less. The BatteryMINDers we sell are all compatible with it, but VDC offers Model 28252 should not be used with the BM-AIK2A because it's maxiumum output is 25A

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