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Old 06-02-2014, 07:21 PM   #1 (permalink)
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Default Can you brown out on a 2s lipo?

Ok guys, i am trying to figure out the cause of a recent crash on my E7. My first crash on this airframe after a year and a half on one setup. I got a "low voltage of 3.3 rail" message as the first error message before some "sensor out of range" type messages. My setup is a 2s 2000mah 20c lipo Y'd into a silver V-bar. Sbus receiver, futabe HV servos. I dont see anything wrong with my wiring to my other electronics, which leads me to believe that i might have just experienced a sag in a lipo that might be wearing out. thoughts?

So what do you think? plausible? Or do i need to keep looking
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Old 06-02-2014, 07:55 PM   #2 (permalink)
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That sounds like your problem. How old is the RX battery? Mine is a 3800mah battery about 1-1/2 old. I noticed that I can't run the same number of cycles per charge as when new.
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Old 06-02-2014, 09:11 PM   #3 (permalink)
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Quote:
Originally Posted by B.Ewing View Post
Ok guys, i am trying to figure out the cause of a recent crash on my E7. My first crash on this airframe after a year and a half on one setup. I got a "low voltage of 3.3 rail" message as the first error message before some "sensor out of range" type messages. My setup is a 2s 2000mah 20c lipo Y'd into a silver V-bar. Sbus receiver, futabe HV servos. I dont see anything wrong with my wiring to my other electronics, which leads me to believe that i might have just experienced a sag in a lipo that might be wearing out. thoughts?

So what do you think? plausible? Or do i need to keep looking
Lipos do go bad but it could be a servo too. Test it on the bench by setting pitch pump to 100 and slam the collective and see if you can reproduce the failure.
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Old 06-03-2014, 10:57 AM   #4 (permalink)
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most likely your battery
a 20c pack even with brushless servos (they can pull alot of juice) should be fine

you shouldnt have to Y cable it
unless your using a stepdown to the s-bus receiver, in which case that might be your issue
it should get power from the sbus cable (mine does)
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Old 06-03-2014, 11:20 AM   #5 (permalink)
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Yes, you can brown out with a 2S lipo.

An old pack or defective pack or a bad cell can do you in.

Do you check the pack voltage under load before each flight?

Do you have two leads going from the Lipo to the electronics? One lead is only good for 5 amps, so even if you have a new lipo of very high capacity, you can only get 5 amps continuous out of it with only one servo type lead.
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Old 06-03-2014, 08:05 PM   #6 (permalink)
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Quote:
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Lipos do go bad but it could be a servo too. Test it on the bench by setting pitch pump to 100 and slam the collective and see if you can reproduce the failure.
wayne, does that test require that i have the servos hooked up? Right now the heli is disassembled so i didnt know if servo arms alone would be adequate to test them.

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Yes, you can brown out with a 2S lipo.

An old pack or defective pack or a bad cell can do you in.

Do you check the pack voltage under load before each flight?

Do you have two leads going from the Lipo to the electronics? One lead is only good for 5 amps, so even if you have a new lipo of very high capacity, you can only get 5 amps continuous out of it with only one servo type lead.
Ok, dumb question, how do you check pack voltage under load? i always just make sure its charged.. i do have 2 leads
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Old 06-03-2014, 10:19 PM   #7 (permalink)
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Quote:
Originally Posted by B.Ewing View Post
wayne, does that test require that i have the servos hooked up? Right now the heli is disassembled so i didnt know if servo arms alone would be adequate to test them.

Ok, dumb question, how do you check pack voltage under load? i always just make sure its charged.. i do have 2 leads
Blair, you do not need the servo arms connected to do the test. They don't even need to be on the heli. With the pitch pump set at 100 its will place a good bit of load anyway.

If you get low voltage during the test it will be recorded in the log and thats the best place to look but voltage min is also on the main screen of the vbar pc interface. The idea is to place a large load and see if you get the brown outs, if you do try a different receiver battery and test again.
If you get low voltage readings with a new receiver pack you you may have a bad servo, test by removing one at a time, or replacing one at a time. Just a process of elimination until you find a problem. Its also possble you have a bad connection or a cut wire rubbing on the carbon frames.
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Old 06-03-2014, 11:15 PM   #8 (permalink)
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Futaba and Duralite both used to make voltage meters that allow you to apply a load to the battery.

I have the Duralite one-you can apply a one or two amp load for a few seconds-this gives a much better indication of battery performance than a meter with no load (which might actually show full voltage).
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Old 06-04-2014, 01:07 AM   #9 (permalink)
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Quote:
Originally Posted by B.Ewing View Post
Ok guys, i am trying to figure out the cause of a recent crash on my E7. My first crash on this airframe after a year and a half on one setup. I got a "low voltage of 3.3 rail" message as the first error message before some "sensor out of range" type messages. My setup is a 2s 2000mah 20c lipo Y'd into a silver V-bar. Sbus receiver, futabe HV servos. I dont see anything wrong with my wiring to my other electronics, which leads me to believe that i might have just experienced a sag in a lipo that might be wearing out. thoughts?

So what do you think? plausible? Or do i need to keep looking
I have had the same experience and 2 x 4700uf 10v capacitors in parallel has fixed the problem.
If your battery was faulty you would have more low voltage warnings in the log.

RX voltage is being monitored continuously. Should it drop below certain thresholds, log entries are being made:

< 4.5 V -> Information only

< 4.0 V -> Warning

< 3.5 V -> Error

< 2.5 V -> Error

< 1.8 V -> Error

These entries are to be taken seriously, you should think about beefing up your power supply. The thresholds help detecting problems early.

The last two thresholds, 2.5 and 1.8 V are being reported if they are crossed for the shortest time, the first three have a short time lag and are being reported after a undercut of a few milliseconds.

Andy
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Old 11-20-2014, 07:39 AM   #10 (permalink)
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Quote:
Originally Posted by flyer2160 View Post
I have had the same experience and 2 x 4700uf 10v capacitors in parallel has fixed the problem.
If your battery was faulty you would have more low voltage warnings in the log.

RX voltage is being monitored continuously. Should it drop below certain thresholds, log entries are being made:

< 4.5 V -> Information only

< 4.0 V -> Warning

< 3.5 V -> Error

< 2.5 V -> Error

< 1.8 V -> Error

These entries are to be taken seriously, you should think about beefing up your power supply. The thresholds help detecting problems early.

The last two thresholds, 2.5 and 1.8 V are being reported if they are crossed for the shortest time, the first three have a short time lag and are being reported after a undercut of a few milliseconds.

Andy
Can you plug a 6800 16v Capacitor into an open spot in the futaba sbus rx? No slots left in my miniv.
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Old 11-20-2014, 07:27 PM   #11 (permalink)
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Can you plug a 6800 16v Capacitor into an open spot in the futaba sbus rx? No slots left in my miniv.
Yes, that is what the vstabi.info site recommends (http://www.vstabi.info/en/node/1422):
Quote:
In our test example it was enough to add one capacitor with 6800 uF for all servos (3 swash, one tail). In some forums they discussed other solutions using special diodes but we could not get a visible effect on the scope with this method.
Sorry, misread your question - I think it is recommended to plug into the vbar power bus. If no slots left most are using a servo y-harness. You could always do a bench test with high pitch pump values and go crazy, if it doesn't brownout or give warnings in the log, it is probably good.
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