Do I really need a TCW back-up battery?

[Dozer]

I cannot take a decision do I need a back-up TCW battery or not.
Please correct me if I am wrong

I am going to install two E-mags which have embedded alternators for ignition.
I will have standby alternator 30A. And it's going to be a Monkworkz' alternator which is "always ON" and doesn't need a battery to work properly.

Even if primary alternator and a battery dies, I will be able to fly with standby alternator.

So why do I need an ISSB?

 

[mountainride]

With out a backup batt you most likely get a brown out when engaging the starter and system voltage drops momentarily. A backup battery would solve this brownout but I used a TCW voltage stabilizer that works perfectly. I would never add another battery. It will most likely be used for keeping avionics alive during start for its entire useful life and then replaced. Voltage Stabilizer in theory works forever.

-Jason

 

[MacCool]

I replaced the PFD and got an IBBS with it, but ended up not using it. I have two PC-680's on the firewall, one is used as an avionics backup. Only one alternator.

 

[Walt]

Worse case scenario is smoke in cabin, flipping off the master is usually step 1, with a BU battery supplying power to PFD/AHRS/GEA24 you still have everything you need.

 

[Carl Froehlich]

SNIP
Even if primary alternator and a battery dies, I will be able to fly with standby alternator.

So why do I need an ISSB?

Your base assumption is the only electrical power failure possible is the loss of the primary alternator. While alternator failure is the most likely fault, it does not present the worst outcome assuming you have a healthy battery (not necessarily a good assumption).

You could have a dozen alternators, but if you have a failure in how you get that power to the panel they do you little good.

I’m not a fan of just adding a plethora of the typical backup batteries as I’ve not seen any that meet my IFR reserve capacity design objectives - and I’ve seen RVs where they were literally dead weight as it becomes easy to overlook their health. I design these out of my planes.

I’ve posted on this many times so I will cut to the chase as I can already envision all the eyes rolling….

My advice, clearly define the mission of your plane. From that create the power distribution design objectives, move on to supporting avionics configuration, then a final system plan. Repeat to refine the final product. I also suggest a critical eye toward maintenance needed to have confidence your setup continues to function as you designed it. This is a quick trip around the loop if you want a day VFR plane.

In this process I assume any single component, wire, switch, ground, junction or avionics can fail and I do not loose the ability to maintain IFR flight. I might be down to one EFIS and one Comm, but with enough electrical power for over two hours of flight.

Carl

 

[Dozer]

With out a backup batt you most likely get a brown out when engaging the starter and system voltage drops momentarily. A backup battery would solve this brownout but I used a TCW voltage stabilizer that works perfectly. I would never add another battery. It will most likely be used for keeping avionics alive during start for its entire useful life and then replaced. Voltage Stabilizer in theory works forever.

-Jason

From my point of view, a IBBS battery is a voltage stabilizer with a battery
The biggest IBBS is 6 Ah and can supply 8 amps continuously and 12 A peak

The biggest stabilizer also runs 8 Amps continuously.

The price is about the same. and anyway 8amps are not enough for all avionics.

 

[Bcone1381]

What values will the voltage fluctuate if the voltage stabilizer is removed and what are the consequences of that fluctuation?

 

[rv6n6r]

I would say that two PMags give you plenty of redundancy - the whole point of the internal generator is to make them independent of an electrical failure.
Which doesn't get you started if you're stranded with a dead battery. But you can supposedly do that by hot-wiring with a 9v battery. I don't carry one of those around but among the various handheld gadgets that we all have, it seems like it would be possible to cobble together enough AAs to also do it. Here's an idea - make up a 6x or 8x AA battery holder > PMag charge connector for your emergency tool kit? Hmm I should do that!

EDIT: I see talk about IFR capacity and power distribution etc. I believe the OP only asked about it as backup for their PMags, so that's all that I'm addressing. I do have a TCW for my EFIS but that's a different issue.

 

[rv8ch]

Your base assumption is the only electrical power failure possible is the loss of the primary alternator. While alternator failure is the most likely fault, it does not present the worst outcome assuming you have a healthy battery (not necessarily a good assumption).

You could have a dozen alternators, but if you have a failure in how you get that power to the panel they do you little good.

I’m not a fan of just adding a plethora of the typical backup batteries as I’ve not seen any that meet my IFR reserve capacity design objectives - and I’ve seen RVs where they were literally dead weight as it becomes easy to overlook their health. I design these out of my planes.

I’ve posted on this many times so I will cut to the chase as I can already envision all the eyes rolling….

My advice, clearly define the mission of your plane. From that create the power distribution design objectives, move on to supporting avionics configuration, then a final system plan. Repeat to refine the final product. I also suggest a critical eye toward maintenance needed to have confidence your setup continues to function as you designed it. This is a quick trip around the loop if you want a day VFR plane.

In this process I assume any single component, wire, switch, ground, junction or avionics can fail and I do not loose the ability to maintain IFR flight. I might be down to one EFIS and one Comm, but with enough electrical power for over two hours of flight.

Carl

Carl nailed it.

 

[avrojockey]

From my point of view, a IBBS battery is a voltage stabilizer with a battery
The biggest IBBS is 6 Ah and can supply 8 amps continuously and 12 A peak

The biggest stabilizer also runs 8 Amps continuously.

The price is about the same. and anyway 8amps are not enough for all avionics.

You might be surprised...I have the small TCW IBBS 3ah and it last an hour with 2 GDUs (full bright), 1 GSU25, 1 GEA, 1 GFC307, GPS175, GAD29, GTX335. I use a handheld com for radio as panel com transmit consumes variable power and battery life becomes a guessing game.

Added bonus...brownout prevention.

I'll probably add the monkworks standby gen...but this is simply for dispatch reliablity to get me home rather than replace alternator on the road

 

[penguin]

There are *a lot* of assumptions behind your question many of which you should review critically as many may well be inaccurate. You don't need an expensive back-up battery, you may feel much more comfortable if one is installed, once you have figured out what you're trying to achieve.

P-mags are not relevant for this discussion. Brown out of your EFIS (your EFIS will reboot during engine cranking) is. Something (battery, power buck, etc) is required to keep the EFIS alive during cranking. Carl has already provided some very relevant thoughts.

I would also look carefully at your power requirements. Are you sure your basic system consumes more than 8A after power shedding post alternator failure? How far, and in what weather conditions, are you assuming you must fly after alternator failure? The certified requirement is for 30 minutes of flight time.

 

[Dozer]

My minimum is 3 hours

Here is a list
# Equipment Brand LRU Current draw, A
1 Display Garmin GDU 460 2.00A
2 Display Garmin GDU 460 2.00A
3 Display Garmin GDU 460 2.00A
4 Autopilot panel Garmin GMC 507 0.20A
5 GPS+NAV+COMM Garmin GTN650Xi 9.62A
6 Oil cooler valve servo TCW CVS-12V-KIT-HD 0.50A
7 Emergency Artex ELT 345 0A
8 Display Garmin G5 0.25A
9 GPS+ADS-B+COMM Garmin GNX 375 7.50A
10 Audio panel Garmin GMA 245 2.31A
11 Air conditioner panel SF Sport Aviation M334 0.50A
12 CO controller CO Guardian 353-101 0.10A
13 Hobb meter Honeywell Hobbs-Digital 0.12A
14 LEDs 6 pcs on instrument panel 0.90A
15 ADAHRS Garmin GSU 25C 0.20A
16 Probe Garmin GTP 59 0.00A
17 Engine Indication System (EIS) GEA 24 0.43A
18 Engine sensor pack Garmin G3X-6CYL 0.50A
19 Compact GPS/Navigation Dat GAD 29C 0.20A
20 GPS WAAS antenna Garmin GA 35 0.00A
21 Electronic Adapter Unit Garmin GAD 27 0.20A
22 STALL indicator Garmin GI 260 0.20A
23 Portable SiriusXM®/ADS-B Receiver GDL 52R 0.29A



1 Roll servo Garmin GSA 28 1.80A
2 Roll Trim motor Ray Allen T3 1.00A
3 Taxi light ZipTip 2.50A
4 Navigating and positioning light ZipTip 1.50A
5 Strobe ZipTip 5.00A
6 Landing light ZipTip 4.00A


1 Taxi light ZipTip 2.5A
2 Navigating and positioning light ZipTip 1.50A
3 Strobe ZipTip 5.00A
4 Landing light ZipTip 4.00A
5 Pitot heat Garmin GAD 26 15.00A

1 Air Conditioner clutch SF Sport Aviation 10.00A
2 Air Conditioner blower SF Sport Aviation 20.00A
3 Tail light AVEO 0.80A
4 YAW servo Garmin GSA 28 1.80A
5 YAW trim motor Ray Allen T3 1.00A
6 Pitch servo Garmin GSA 28 1.80A
7 Pitch trim motor Ray Allen T3 1.00A




1 Upper console lights SF Sport Aviation 5.00A
2 USB outlet Garmin 5.00A


3 USB outlet Garmin 5.00A

 

[penguin]

You're so far out of the real world you need some serious help...