mark.bitterlich(at)navy.m
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 Posted: Sun May 14, 2017 11:26 am Post subject: [Non-DoD Source] Re: Generator failure/ loss of electrical |
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Hans O, I really do NOT want to sell my 50. It has been a true love affair, but I am moving on and it might turn into a simple matter of money.... Yes, you're correct ... when the 50 goes, I don't think I will hang out on the Yak List anymore. There are a LOT of nice folks there, but too many of the other kind. You might have noticed that I do not comment on there very much anymore.
Thanks for writing, and I hope all turns out well with your radio issue!
Mark
________________________________________
From: owner-yak-list-server(at)matronics.com [owner-yak-list-server(at)matronics.com] on behalf of Hans Oortman [pa3arw(at)ziggo.nl]
Sent: Sunday, May 14, 2017 4:34 AM
To: yak-list(at)matronics.com
Subject: [Non-DoD Source] Re: Generator failure/ loss of electrical power
Good story Mark and very true!
BTW: the batteries in my Yak52 were put in there in 2002 when I picked her
up in Lithuania. Until now they have never let me down and have not been
replaced yet. All other things original Russian with the good old dc
generator.
Sad to read y're gone probably sell yr Yak50....so w're possibly gone miss
you here on the net??
Regards,
Hans O.
PH-YAK
Op 14-05-17 01:08, Bitterlich, Mark G CIV NAVAIR, WD
<mark.bitterlich(at)navy.mil> schreef:
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<mark.bitterlich(at)navy.mil>
There are a couple of folks that have already commented on the proper setting
for the generator voltage, and I want everyone reading this to know that I
have high regard and respect for everyone that commented. They have also said
some very nice things about me, for which I am gratified. This is going to be
a long discussion, so be fore-warned. If you donıt like listening to Mark
talk, then just stop right here and discard the message. OK? That should
stop some of the flak from the peanut gallery. Be aware that I rarely write
up explanations like this anymore, so donıt worry this is an exception to the
rule.
So with that said, there is a part of me that does not even want to discuss
this, but what the heck, I hope I donıt lose any friends.
First of all, EVERYBODY is correct in what they said regarding this topic. No
one is wrong. That is kind of a unique situation really, but factually it is
the truth.
First of all, there was a reference to the Yak manuals, and what they say the
proper output voltage of the generator should be set to. Yes, they all
specify over 28 volts DC, and that is for a number of reasons. All of the
equipment in these aircraft, namely engine instruments, voltage inverters for
gyroıs, pitot heat, radios, and on and on ALL of these things were designed
to operate at the specified voltage of 28 volts, or 28.5 VDC. The original
battery in these aircraft was typically a Nickel Cadmium design, and the
charging voltage for this battery also met the design generator output voltage
specified in the publications.
But then these aircraft came to the United States, and people started
immediately pulling out the original NiCad battery (which was pretty much
impossible to maintain) and started replacing it with two 12 volt gel cell
batteries. Some of the really serious aerobatic types installed two very
light weight and minimum capacity batteries, and in my opinion this was a
serious mistake. These batteries combined with the B&C PMG Alternator (the 10
amp version) could combine to cause serious damage to avionics components, and
Iıve watched it happen a few times now, regardless of the warnings I have
given to a few owners. Most of them finally learned, use different batteries
(yes, Gel Cell too), but larger, and with a better alternator like the B&C
SK-35, which is a wonderful design with the LS1A regulator.
Getting back to gel cell batteries. If you read the fine print that usually
comes with these batteries, you will see that they have a MAXIMUM RECOMMENDED
CHARGING CURRENT! Charging current is typically controlled by varying
charging voltage on the fly. One problem the YAK and CJ aircraft do not
have an inherent system for controlling charging current, voltage yes, current
no.
So here we have a conundrum. We are installing gel cell batteries that
typically have smaller inherent capacity than what was originally installed.
This a very important point. Further, they are a different TYPE of battery
than was originally installed, and they are supposed to be charged at a lower
CURRENT than what was originally assumed.
So if you leave your voltage set for 28.5 VDC or whatever the Russian manual
says, then it is going to result in a little bit too high of a charging
current for the gel cell batteries as recommended by the manufactuer. This
will then cause the batteries to gas, and once that happens battery capacity
diminishes. Note: Causing a gel cell to gas is bad business. But then to be
honest, all batteries die eventually. You can extend their life by using
fancy chargers like Battery Minders (I like these a lot by the way), which
will shoot a short blast of HF energy around 3 MHz into the battery to help
recombine sulfates back into acid and off the plates but in the end, they all
go bad.
The important thing is to know that you need to check them. Five years is
indeed a long time for battery life in these aircraft, but it is feasible if
you have spent a lot of effort watching charging current and using chargers
like the Battery Minder brand.
What is important to understand is the way generators work. A generator has a
plus and minus connection that outputs voltage correct? Yes it does. But
when the generator is not turning, the PLUS connection on it is essentially a
dead short to ground. That is a bad bad thing to have your battery connected
to. If you connect a good battery to a dead short to ground, there is going
to be a lot of current flowing, and fuses will blow, relays will burn out and
wires can melt. It is a very very bad thing.
As a generator starts spinning slower and slower . Like when your M-14P
engine is coming back to idle, it is not spinning fast enough to deliver a
voltage higher than what is in your battery. At that point, current starts
flowing BACKWARDS or IN REVERSE to your generator FROM the battery. The
slower the generator spins, the less voltage it will then produce and the more
current will flow back into the generator from the battery.
The DMR-200 Combined Relay device is put in there to control this situation.
Remember my previous post about the MAIN CONTACTOR RELAY. This relay is what
connects the generator to the main electrical bus of the aircraft, and thus
the battery as well. When current starts flowing backwards into the generator
from the battery, there is a special device called THE REVERSE CURRENT RELAY
that senses this. Once that current gets high enough, it will cause the MAIN
CONTACTOR RELAY TO OPEN (!!!!) thus disconnecting the generator from the rest
of the aircraft. TA-DA! Problem solved! And yes, that is when the Generator
light comes on!
But letıs say you have some weak half assed batteries, that you are trying to
get the last bit of life out of, because you are too cheap to buy new ones.
Sorry, sometimes I get carried away, but it is the truth. People have done
this all the time, and I have watched them do it.
Now when your generator slows down, you start getting reverse current, but the
battery is so darn weak, it cannot supply ENOUGH current to cause the reverse
current relay to sense it. Now you start to have a voltage droop in the
aircraft. Voltage goes lower and lower as the weak batteries discharge more
and more. So now instead of a quick disconnect of the generator, you instead
get a lower and lower battery supply voltage to EVERYTHING in the aircraft
that is designed to run off 28 volts. Radios, Transponders, GPSıs, you name
it. They are now all being subjected to a lower voltage than they were
designed to operate with. Sometimes they have had enough and fail. Whoıs
fault is that? Yep yours, the aircraft owner.
So batteries need to be checked. The easiest way is to put a fairly good load
on the batteries and verify that their voltage does not drop too low. If you
are not up for that, then a good idea is to just replace them every few years
and be done with it.
So I took the time to write this. I hope it was useful to you. Feel free to
write me directly if you disagree, or have a technical input that you feel I
missed. I very well could have. This whole thing is like a string of
Dominoes going down, but you need to keep it in mind.
So yes, you can lower the charging voltage to try and limit charging current
to gel cells, but this is also a two edged sword. My input is to leave it
where the manual says it should be set to, use a Battery Minder charger with a
sulfate blaster at 3.4 MHz, and just bite the bullet and replace those
batteries on a regular basis, and donıt use itsy-bitsy batteries dumb move
Kemo Sabi.
Mark Bitterlich
Whoıs YAK-50 is probably going up for sale.
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