Was considering installing a second battery instead of a TCW backup battery given the use of the ULPower engine with dual electric fuel pumps and an electric engine controller. I was thinking about isolating the battery behind a solenoid and having a switch for “Aux Battery”. I would use this battery for the backup on the EFIS as well so no voltage drop with engine start, then engage the battery in flight to allow for charging. If one battery is the PC680 and the other is an EarthX, would this be a problem? Thanks in advance.
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Dual Battery
- Thread starter R7237
- Start date
Larry DeCamp
Well Known Member
Relevant question
Can the LiFe and AGM battery share the master firewall ground point for cabin loads and engine ?
Can the LiFe and AGM battery share the master firewall ground point for cabin loads and engine ?
I would think it dosent matter, but know the EarthX likes 13.4V and not sure what that means if it is put in parallel with the PC680 to be charged by an alternator. Maybe the answer is 2 EarthX and not a “mixed” system, but figured someone on here might know the right answer.
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Your aircraft has only one airframe gound. It doesn't really matter where the battery connects to that ground. Battery chemistry has no relevance to the electron path to the load.
Carl Froehlich
Well Known Member
While the different battery chemistry is an issue, I note that your plan to manually put batteries on line and off is problematic. Some thoughts:
- As you are running an electrically dependent engine, I recommend using the unique requirements of that setup as the basis for your power distribution design. I suspect two things will fall out of this process; you will find dual batteries a hard requirement, and a byproduct will be this creates the redundant panel power you want.
- After you do the above I also suspect you will find that two identical batteries better meet the need, provide backup modes for reliability, and simplify operation and maintainance.
- Panel brown out tends to not be an issue if you maintain the batteries (a hard requirement for an electrically dependent engine). That said, I know the Dynon SkyView handles voltage sag during engine start very well. I do not have the same faith with the Garmin GTN-650, so I start the engine with that side of the panel off, leaving only one SkyView display up during start.
- Manual procedures to keep a battery charged in an electrically dependent airplane is, in my opinion, asking for trouble.
Carl
From the earthX website:
Can I hook an EarthX battery in parallel or series with a lead acid battery?
No. The voltages are not the same and you will over charge the lead acid battery and drain the lithium.
It is best to follow the manufacturer's recommendations.
However, since the alternator charging voltage is over 14 volts, it seems that both
batteries would see that 14+ voltage and not the voltage of the other battery.
The two batteries should be electrically isolated when not being charged by the alternator.
Talk to EarthX first.
Can I hook an EarthX battery in parallel or series with a lead acid battery?
No. The voltages are not the same and you will over charge the lead acid battery and drain the lithium.
It is best to follow the manufacturer's recommendations.
However, since the alternator charging voltage is over 14 volts, it seems that both
batteries would see that 14+ voltage and not the voltage of the other battery.
The two batteries should be electrically isolated when not being charged by the alternator.
Talk to EarthX first.
Definately follow the mfg guidelines for the positive side of the battery. However, please exercise caution if you plan to isolate the ground side, as that is generally a BAD idea. Do your research.
As Carl mentions, mixing different chemistries in the same system, except for isolated backup only, is generally a bad idea for several reasons. However, that was not the OP's question.
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Electrically dependent engine
These comments have been very helpful. Yes, the engine is completely electrically dependent from the dual electric fuel pumps as well as the ECU. Alternator is a permanent magnet engine mounted. My thought is that the second battery provides two purposes. In the case of an alternator failure, I have more time to respond, and a second battery hopefully gives me options as well as a nice backup battery source. Looks like I will need two EarthX, with one running critical components and connected to the alternator field with the master. Is it not a good idea to connect the other one with an AUX battery switch?
These comments have been very helpful. Yes, the engine is completely electrically dependent from the dual electric fuel pumps as well as the ECU. Alternator is a permanent magnet engine mounted. My thought is that the second battery provides two purposes. In the case of an alternator failure, I have more time to respond, and a second battery hopefully gives me options as well as a nice backup battery source. Looks like I will need two EarthX, with one running critical components and connected to the alternator field with the master. Is it not a good idea to connect the other one with an AUX battery switch?
Carl Froehlich
Well Known Member
What is the alternator’s output rating?
My short answer is no. The longer answer requires much more information on your design thoughts and capability objectives.
Carl
Redundant electrical system
I have two Surefly electronic ignition on my IO-360, two alternators and
two LiFePo batteries. The second alternator has a standby regulator with a
0,5 V lower voltage setting.
The electronic ignitions get their power from each of the batteries.
A single failure does not warrant any action, I get an alarm.
The alternators and the batteries can be separated with one switch.
You realy need to think it through all possible failure modes.
I have two Surefly electronic ignition on my IO-360, two alternators and
two LiFePo batteries. The second alternator has a standby regulator with a
0,5 V lower voltage setting.
The electronic ignitions get their power from each of the batteries.
A single failure does not warrant any action, I get an alarm.
The alternators and the batteries can be separated with one switch.
You realy need to think it through all possible failure modes.
Alternator is 50 amp.
Electrical system is wired using a VPX Sport.
Main fuel pump and ECU wired off the main bus thru fuses.
LED lighting and a heated Pitot.
Backup “boost” pump wires thru the VPX.
EFIS is AFS 5500 and a TT AP.
Single COM and NAV radio.
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In my CH601, I used a DakotaLitium 10AH LIfePo4 as an auxiliary battery. It is charged using a DC DC step up step down buck boost device. This allows to set the charging voltage precisely and also to set the maximum charging current as well as cut off minimum voltage (so the charger runs only when the alternator runs). It is important that this is isolated from the main bus so that this is not attempting to charge or get charged by the main bus directly. Total separation with switches / relays is an option or for always live standby, Schottky diodes. See the device: https://www.aliexpress.com/item/32844080988.html?spm=a2g0s.9042311.0.0.120f4c4dcQyAID
I am now considering installing this on my RV6 to provide an alternate feed to the VHF, EFIS and engine instruments.
I am now considering installing this on my RV6 to provide an alternate feed to the VHF, EFIS and engine instruments.
There are models that will work down to 5V. It would do in my opinion the same thing as the branded IPS power stabilizer device, except this would be for $10 instead of hundreds. To watch for. The operating temperature range is often not specified.... I ordered some where I did not pay attention to this and I hesitate to use them.
I have three of these (5 amp rated) gang'ed together to make a 24V supply for my 430. Howevever, I don't believe that I would trust them at my battery connection where a failure would knock out my whole elec system.
