Need help on charging the battery??

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Reaper30
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Need help on charging the battery??

Post by Reaper30 »

I recently purchased a 2002 DA 40-180/steam gauge 530w/430 in great condition! It's been a blast so far. However, after reading a number of threads about the best device and different ways to keep the battery charged and preventative maintenance on the battery, it seems there are some differences on the procedures. I know that this aircraft has a three prong EPU connector to connect a charger/power supply. Some say you can charge the battery through the three prong connector, others say you can only charge the battery by connecting the charger to the battery via connectors. What I am trying find out, since I want both a power supply and a battery charger in one (without out buying two different devices), is how can I use the three prong connector to conduct both operations of keeping the battery charged (trickle type charge) and use it as a power supply? Is there a device (Battery Minder or other reasonably priced unit) that uses the EPU connector to charge the battery and provide power to run avionics? And what procedures (disconnect battery, pull breakers, master on etc...) would I do to be able to use the EPU connector as a battery charger?

Sorry to be long winded but it seems that I would need two different devices: one to charge the battery and the other to utilize as a power supply! I hope this isn't the case!!!

Thanks for any information! Great forum too!!
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Re: Need help on charging the battery??

Post by CFIDave »

I own a combination 28VDC aircraft APU and battery charger that will provide both functions you're asking for:
- charge your battery
- provide ground power for running avionics
AND do both of these through the external power plug built into the DA40.

Here's the unit I bought from Aircraft Spruce:
Part number 11-08146 APU BAT CHGR CESSNA PLUG 28V
https://www.aircraftspruce.com/categori ... harge.html

You do have to remember to throw a switch on the unit to switch between these two modes of operation. And when charging the DA40 battery through the plane's external power plug you need to pull the 70A BATT circuit breaker to disconnect the plane's electrical system downstream of the battery.

But the unit has worked well for me.
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Chris B
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Re: Need help on charging the battery??

Post by Chris B »

The device Dave linked looks very nice. But if cost is your main concern, then it is cheaper to buy a Battery Minder (Link) and Schauer charger (Link) which can be used as a ground power supply. This is the route that I've taken.

The AGM battery in the DA40 is ridiculously expensive, so IMO it is cost-effective to coddle it for maximum life. The best way to extend the life of lead-acid batteries is to a) avoid complete discharge (very hard on lead-acid), and b) keep them 100% charged ("float") when not in use. So I run the Battery Minder harness up near the oil dipstick with a service loop that reaches through the access port, and leave it attached whenever I can. It is light enough (3 lbs?) to carry in the plane.

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Re: Need help on charging the battery??

Post by rwtucker »

So far, I have had pretty good luck using a maintainer/desulphator (http://batteryminders.com/store.php?spa ... e&&app=air). They have a 24 volt model optimized for aircraft lead-acid batteries (which are slightly different than most non-aero types). I think I paid about $125. The only downside is that it's circuitry senses battery condition before applying current. This means that it won't trip the relay on the EPU system so you have to connect it directly. I have had the original battery since the DA40 was built in December 2007. It still cranks full speed even though I ran it down to zip one time by leaving a map light on for a week or so (as Chris said, very hard on lead-acid batteries). If I were starting over, I might look for another brand of maintainer/desulphator that would apply current first so you could have the convenience of the EPU. As is, I connect the maintainer/desulphator a few times a year and let it work for a week or two when I'm not flying it. It takes me about a week to do my annual so it always gets a good run then.
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Re: Need help on charging the battery??

Post by Reaper30 »

Dave,

After pulling the 70 Amp Batt breaker, do you have to flip the Master (Bat) switch on to complete the circuit? Also, if the circuit breaker is pulled, does the Hobbs meter run?

Thx for the responses!

Bob
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Re: Need help on charging the battery??

Post by CFIDave »

Yes, you have to turn the Battery switch ON to complete the circuit. This activates the Battery relay which connects the main battery to the Battery bus (which in turn is connected to the External Power Connector via the Ext Power relay).

But the Hobbs/Hourmeter doesn't run while the battery is being charged. This is because (on a Lycoming engine DA40) electrical current to the Hobbs relay flows only when the oil pressure switch is activated -- see wiring diagram DA4-9231-20-02 in the DA40 Aircraft Maintenance Manual.
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Re: Need help on charging the battery??

Post by Rick »

CFIDave wrote:... electrical current to the Hobbs relay flows only when the oil pressure switch is activated ...
or when the battery voltage drops below some low threshhold while the battery is going dead! :shock:
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Re: Need help on charging the battery??

Post by rwtucker »

Rick, Your point hit me the one time I left a map light on a week or so and drained the battery. I put something like 100 hours on my Hobbs. So . . . the inference is that the oil pressure relay is NC and closes at a higher voltage than is required to keep the Hobbs ticking? Makes sense. An old Hobbs I have in a drawer takes 6-48 volts input. A typical mechanical DC relay in that setting might require 22v to close and drop at 19v. (I don't know if the relay is mechanical.) Too bad. A small wiring change would eliminate that scenario.
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Re: Need help on charging the battery??

Post by Rick »

rwtucker wrote:Rick, Your point hit me the one time I left a map light on a week or so and drained the battery. I put something like 100 hours on my Hobbs. So . . . the inference is that the oil pressure relay is NC and closes at a higher voltage than is required to keep the Hobbs ticking? Makes sense. An old Hobbs I have in a drawer takes 6-48 volts input. A typical mechanical DC relay in that setting might require 22v to close and drop at 19v. (I don't know if the relay is mechanical.) Too bad. A small wiring change would eliminate that scenario.
Yeah, this is a 'known' problem with the Diamonds - the factory will admit to it if you ask them. I believe nobody thought about the effects of leaving the map light on, and your analysis is exactly correct. When the voltage drops below about 20 volts, the Hobbs kicks on and runs until the battery drops below like 6 volts. It's a 'feature'!

Another good reason to 'upgrade' to the LED map light(s) (at least the pilot side light)...
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Re: Need help on charging the battery??

Post by Rich »

rwtucker wrote:Rick, Your point hit me the one time I left a map light on a week or so and drained the battery. I put something like 100 hours on my Hobbs. So . . . the inference is that the oil pressure relay is NC and closes at a higher voltage than is required to keep the Hobbs ticking? Makes sense. An old Hobbs I have in a drawer takes 6-48 volts input. A typical mechanical DC relay in that setting might require 22v to close and drop at 19v. (I don't know if the relay is mechanical.) Too bad. A small wiring change would eliminate that scenario.
This has been bugging me (theoretically, since I haven't been bitten - yet). Digging through the wiring diagrams and the IPC still has me scratching my head. As far as I can determine:

1. There is no oil pressure "relay". It's just a NC pressure switch. This has double duty and would be tricky to change. In addition to dropping out the hobbs relay (thereby starting the hobbs) on pressure detection, it activates the "Low Oil Pressure" annunciator when the pressure drops off and it closes. I don't think this is a DT switch.
2. There is no workable cross-reference between the wiring diagrams and the IPC. I think the relay is a VF4-45H11. It is a SPDT relay, so in theory, wiring this differently could conceivably remedy the problem.
3. The very confusing thing is it would appear this relay draws 66.7 mA when powered. This would seem to be way too much, as you'd lose 1 Ah from the battery every 15 hours the plane was parked. That makes no sense, so I'm doubting I have the right relay.
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