Fuses on the panel, or not

For a very clean power distribution option, have a look at

http://www.powerwerx.com/powerpole-power-distribution/

Anderson 15A Powerpole connections for all the instruments, with blade fuses on master and all outputs.
Alternatively, there are fused Power Distribution blocks without Powerpoles on the "fuses & circuit protection" page.
Jim

On Friday, October 18, 2013 8:23:28 AM UTC-7, wrote:

I would appreciate a steer to any small mini-blade fuse blocks or low amp mini-fuses.

On Saturday, October 19, 2013 3:34:50 PM UTC-4, JS wrote:
For a very clean power distribution option, have a look at



http://www.powerwerx.com/powerpole-power-distribution/

Aside from the expense what about http://www.powerwerx.com/powerpole-p...orizontal.html

and also assuming you have space for this near the instruments.

On Wednesday, October 16, 2013 5:26:48 PM UTC-4, Dave Nadler wrote:
Please don't install glass fuses, because they are prone to:

- blowing under vibration (like, rolling during launch)

- even more prone to blowing in gas-powered motorgliders

- corroding and introducing voltage drop at the (non-gas-tight) ends

The voltage drop breakers introduce can be significant and can cause problems.

Use blade types inline (not on the panel!) and avoid these problems...

Hope that helps,

Best Regards, Dave "YO electric"

Can blade fuses be installed in type certified gliders?

On Tuesday, October 15, 2013 8:39:59 AM UTC-7, 7C wrote:
2) Thermal trips need a large overcurrent for a long time before they go.

Low value trips introduce a large voltage drop.



I would add to this that thermal trips will reset after a period of time. If the original short persists they will cycle on and off quite quickly (in my experience a few times a second) and will NOT protect equipment from overheating. I had them on my batteries and got lucky to that the output to the 5V converter shorted on the ground - the 12 to 5v converter overheated, caused a permanent short and ended up well above too hot to touch. I now have a normal fuse and redundancy provided by a second battery.



I would be concerned that any self-resetting circuit would behave the same, perhaps with a longer cycle. If you can't physically isolate then you are stuffed when you are flying... Bet you can't land quickly enough

Uh? Why are you talking about "thermal trips" and automatic resetting? These thingies are called circuit breakers. Yes they they internally thermally trip, but so what. An aviation circuit breaker like the popular Klixon "TC" product lines will not automatically reset. You've got to push 'em back in.. For good reason.

Darryl

On Wednesday, October 16, 2013 12:42:06 PM UTC-7, JohnDeRosa wrote:
A couple of comments about circuit protection some of which has been covered before in other threads;



- Pete Purdie's comment above about undersized wiring is on target. Bigger is better (within reason)! If you saw smoke you probably do not have Tefzel wiring. Get some!

- Fuses are great as they are cheap, fast acting and have ZERO voltage drop across its terminals. Cons are that they are more difficult to replace in flight and somewhat fragile (glass type).

Capitalized ZERO, like you really mean absolutely zero, nothing, zilch, nada? Ah in a word. No. A fuse will *not* have ZERO voltage drop. A fuse relies on resistance in the fuse element causing heating and mechanical failure of the element. A typical fuse for a few amp applciation might have a voltage drop of ~100mV to ~200mV drop at the fuse rated current, and that depending on the fuse type and ratings). If there was zero resistance the fuse would never work. Since there is resistance there will be a voltage drop. Now that voltage drop may be a lot less than a similar spec circuit breaker, especially for low trip current applications. And in both cases is not a simple linear relationship, vendors typically provide voltage drop as a part of the spec sheet of their fuses and breaker products and fuse specs will include both that drop at rated current and a cold resistance value.

On Tuesday, October 15, 2013 1:23:20 AM UTC-7, Jim White wrote:
I agonised over this when I re did my own panel. My conclusions we

1) I would not reset or replace a fuse in flight so did not need them on
the panel.

2) Thermal trips need a large overcurrent for a long time before they go.
Low value trips introduce a large voltage drop.

So, I fitted in line blade fuses for all my equipment and use the panel

space for other things. I did buy a fuse block but decided it was too big

and made the wiring cumbersome.

Jim

I bought and tested Klixon CBs and the standard German panel mounted fuses when I re-did my panel last winter. The CBs had a significant voltage drop - corresponding to about 20 minutes of battery life at the end of a flight if I recall correctly. I was unwilling to give up the extra duration off my battery, so I stayed with fuses.

My panel is curved and my instruments are basically square behind the panel so there were several good triangular-shaped spots that could accommodate up to 5 panel-mounted fuse holders. I have never replaced a fuse in flight, but I could imagine a circumstance where a current spike (maybe from keying the radio) could blow a fuse that I might want to replace. Plus it's easier not to have to take off the canopy to get behind the panel. I've seen fuses mounted in the leg tunnel under the panel, which is an interesting alternative.

I'm a little nervous about putting automotive parts in my glider - for instance, I replaced all my wiring with Tefzel after experimenting with high current through the vinyl shielded Radio Shack variety.

9B

On Sunday, October 20, 2013 2:11:39 PM UTC-4, wrote:
I'm a little nervous about putting automotive parts in my glider

You mean, for example, old-style automotive glass fuses, given
up by the auto industry as too unreliable some decades ago ???

Please do not put ANYTHING from RadioShack in a glider panel...

On Sunday, October 20, 2013 1:07:38 PM UTC-4, Darryl Ramm wrote:
Uh? Why are you talking about "thermal trips" and
automatic resetting?

Hi Darryl - I think he's talking about PTCs, which are
appropriate in some situations but not here...

On Sunday, October 20, 2013 12:23:18 PM UTC-7, Dave Nadler wrote:
On Sunday, October 20, 2013 1:07:38 PM UTC-4, Darryl Ramm wrote:

Uh? Why are you talking about "thermal trips" and

automatic resetting?



Hi Darryl - I think he's talking about PTCs, which are

appropriate in some situations but not here...

Hi Dave - yes, hopefully common sense would prevent their use. And automatic resetting breakers are also forbidden by CFR 14 23.1357. But part 23 may not apply to a JAR-22 derived type certificate on a glider but its a good place to get input on ways to do things and what an A&P/DAR/FSDO would like to see. Folks really ought to think Klixon type breakers if using a breaker on gliders.

Folks might also want to note the requirement in CFR 14 23.1357 for the fuses to be replaceable in flight if critical and the need to carry spares. So you might be able to argue that some non-critical fuses can be placed behind the panel but others will clearly fail that requirement. I'd not want to argue with the FAA for example that the fuel pump or engine controller fuse holders and replacement fuses in a motorglider don't need to be accessible to the pilot.

Also see FAA AC 43.13 Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair. Chapter 11 (Electrical Systems). Lots of good stuff there that should be read by anybody who is considering messing around with any aircraft wiring, not all of it applies to gliders however. And as promoted before on r.a.s. there is lots of advice on aircraft wiring on this web site. http://www.aeroelectric.com/articles.html (mostly intended for home builders of power aircraft)

---

And... if working on any aircraft start with talking with a local A&P (or maybe an EAA homebuilder or similar), if certified they'll need the A&P will need to sign off on what you do (or do it for you), if experiential you want their advice and likely a look over what you are planning to do/have done. There is a lot to gain by actually having somebody look over your shoulder that you can't get off r.a.s.

The most important place for circuit breakers is right at the battery, typically a 5A or 10A breaker mounted on the battery or right next to it that will protect your aircraft/wiring harness from a fire caused by a dead short.. I would use a breaker for that, easy to reset, never missing a replacement fuse etc. and the voltage drop is relatively insignificant for these higher current breakers. That primary circuit protection is in JAR-22 but is unfortunately vague.

What you do downsteam for there is more complex, some avionics/device vendors will spec a slow or some cases fast blow fuse to protect delicate devices, some will say a breaker is OK. Read the documentation. Get advice from somebody experienced with this stuff who can look at exactly what you are doing. Note the FAR and JAR requirements for each "critical"/"saftey of flight" device to have its own separate overload protection, and just good common sense as well.

Darryl

On Sunday, October 20, 2013 12:31:32 PM UTC-5, Darryl Ramm wrote:

Capitalized ZERO, like you really mean absolutely zero, nothing, zilch, nada?
Ah in a word. No. A fuse will *not* have ZERO voltage drop. A typical fuse
for a few amp application might have a voltage drop of ~100mV to ~200mV drop
at the fuse rated current, and that depending on the fuse type and ratings).

Darryl - Mea Culpa. Yep, you got me on that one. Maybe I will do better this time.

Both fuses and breakers have an internal resistance which translates into a voltage drop (which depends on how much current you are drawing). Lets talk about a 1A load for nice round numbers (YMMV).

Littlefuse 3AG fuse specifications (common glass tube);

Rating Internal Voltage Drop Voltage Drop
Resistance at rated Current at 1A
==== ========== ================ ============
1A 0.19 0.19 0.19
2A 0.07 0.14 0.07
3A 0.04 0.13 0.04
4A 0.03 0.12 0.03
5A 0.02 0.11 0.02

Klixon CT series breaker specifications;

Rating Internal Volts Drop Voltage drop
Resistance at rating current at 1A
==== ========== ================ ============
1A 1.10 1.10 1.10
2A 0.35 0.70 0.35
3A 0.13 0.40 0.13
4A 0.09 0.37 0.09
5A 0.07 0.35 0.07

Take aways;

- Fuses have significantly lower voltage drops than breakers by an average of 4x ... but it AIN'T ZERO!
- The higher the current circuit protection device rating, the less voltage drop.
- Covering your panel with low rated fuses or breakers for each and every instrument isn't a good idea.
- Circuit protection devices in series with another device compounds the problem. For example a master fuse sourcing individual device fuses. Each layer drops more voltage.
- As had been said over and over again in this and other RAS threads, and bears repeating, a single large value fuse at the battery is your single best overall safety bet.
- One last thing - Per most manufacturers breakers should not be used as on/off switches. The only one I have found that can be used as an on/off switch is the Tyco W30 and W31 series.

- John