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Old 09-19-2010, 03:18 AM   #281 (permalink)
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Ah see... So I wasn't completely high . I swear I hooked it up exactly like Bob said.
So it seems that DxFlyer burned out two Optima RX's hooking the SPC port to the lipo on the neg side of the ESC too.

So Dxflyer, it looks like you power the SPC from the actual serial harness while I was charging the SPC from the balancing tab. I like your way better. Less points of failure.

This is all getting very interesting.

So the Diode keeps a short from damaging the RX? It's like you will get that initial short when you first plug everything up and the diode is kind of a check valve to stop the wrong direction of current initially and then everything goes back to the correct direction...

Mike
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Old 09-19-2010, 11:35 AM   #282 (permalink)
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Damn ground loops. Good catch DXflyer.... I had not thought of that loop.... Ground loops are just a bad thing! Yes you are getting a ground leakage through the SPC port when hooking up pack 1 positive side (your diagram) first. It does not make sense that when you then hook up pack 2 negative side (your diagram) it blows the RX But I believe you that it does. Again ground loops are a bad thing! I don't think all this would happen if you plugged in pack 2 (negative) first. But who wants to try and remember that every time out at the field!

I see another fix however. Just do not hook up the ground line at all to the SPC port. First, it now wont cause any ground loops (which is a good thing) and 2nd, nothing will power up at all until everything is hooked up!

I used a meter to confirm inside the RX the servo buss and the SPC ground are in fact tied together. I also checked several ESC I have and input ground and BEC ground are also tied together.

Finally either way you go diode or remove the SPC ground wire, you still have to remember to hook positive to the SPC port from the negative side pack balance port! If you accidentally hook the positive side pack balance port, with the diode or removal of the SPC ground wire, you now will provide the full 12S to the SPC port!

Bob
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Old 09-19-2010, 12:07 PM   #283 (permalink)
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So what is going to be the best way to do this?

No ground to spc? Power spc from the serial harness on the positive lead from the neg side lipo?

Plug the lipo's in individually instead of all at once?
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Old 09-19-2010, 01:59 PM   #284 (permalink)
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Okay. I had several flights at the field and it works great. Again I use the diode way. Also, I prefer not to use the balance plug. Eventually I will try just the one wire that Bob mentioned next week if I don't get lazy. I hope this helps people from blowing their rx.
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Old 09-19-2010, 04:09 PM   #285 (permalink)
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Dxflyer.
Awesome. So you did it exactly like the diagram? Do both lipo's get plugged in at the same time?
Or does that matter? What diode did you use on the positive lead of the SPC cable?
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Old 09-19-2010, 04:15 PM   #286 (permalink)
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FYI more discussion going on here about the diode vs no SPC ground.
http://www.rcgroups.com/forums/showt...96037&page=640

The bottom line looks like the diode is a good way BUT because of it's little bit of resistance in the current flow direction it may throw off the telemetry voltage reading a little. Just adjust your low voltage alarm accordingly.

Maarset or anyone, even with this fix, you still MUST always use the negative side pack balance port to the SPC. If you plug in the positive side pack balancer port you will still get POOF....

Bob
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Old 09-19-2010, 04:32 PM   #287 (permalink)
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Maarset / DXflyer, I just also realized something that for maarset could still be a potential problem. Dxflyer you are not trying to use the balance port on a pack for SPC power. Your drawing shows coming off the main power connectors. maarset still has to be careful using the balance port because it is a 3rd connection.

Using your drawing if he was to plug in pack 1 (positive side pack) to the ESC and then plug in the SPC balance port to pack 2 (negative side pack) the ground loop would also power up the ESC and thus all current would now be going through the balance tap ground. Not too good.

maarset you have to use a plug in order if your going to use the balance port.
Plug in the balance tap to SPC first so RX has signal. Plug in the low negative side pack 2nd and then plug in the high positive side pack to power up the ESC. In fact if you do this in this order 100% you do not even need the diode although I would add it to stop positive side spikes as you know the spark you get when plugging in the ESC.

Bob
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Old 09-19-2010, 07:08 PM   #288 (permalink)
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Quote:
Originally Posted by maarset View Post
Dxflyer.
Awesome. So you did it exactly like the diagram? Do both lipo's get plugged in at the same time?
Or does that matter? What diode did you use on the positive lead of the SPC cable?
I did exactly like the diagram. I plug one lipo at a time. I plug the lipo to the side connected to the spc/ground and then the second lipo. I dont think it matters but to be safe I plug it this way first. I had about 10 flights today and no hiccups . Maarset I would recommend not using the balance plug because of many reasons. One being what Bob said. I know its convenient but this could add another failure point. You have to worry about the order too.

The diode way does reduce the voltage a little bit but I just adjust the transmitter to compensate. This telemetry really makes flying a little less to worry about, before with the time we just guess. I toasted some lipos that way by going way below the 20% mark.

The diode I use is nte5801just because I had it lying around. This might be overkill and you can get away with a smaller diode but it works. If someone else has a different diode that works please let us know.
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Old 09-19-2010, 10:54 PM   #289 (permalink)
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Thanks everyone for the great detective work on the serial pack monitoring issue.

It is hard to avoid the conclusion that we are jumping through hoops to get around a design problem in the receiver.

I don't like adding failure points like a diode in the wire to the SPC but it is good to know it works.

Given that voltage monitoring via the SPC port was a major sales feature it is disappointing that there appears to have been inadequate testing of such a common pack configuration.

It would be good to hear from Mike what ( if anything ) Hitec plan to do about this as I can see at lot of people blowing receivers in the months ahead ...
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Old 09-19-2010, 11:40 PM   #290 (permalink)
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I am not sure I would call this a design problem. Sure it would have been nice to have a blocking diode in the RX for reverse polarity protection but in the end using balance ports and other ways to connect, you have to be aware of what your doing and loops. As I said way earlier I have known many that have blown up charge balancers doing the same kind of thing like putting a 2 pack series setup and plugging in the balance connectors in the wrong order! The diode could be eliminated simply by making sure you plug in the packs in the correct order.

Bob
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Old 09-19-2010, 11:58 PM   #291 (permalink)
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I take your point, but if I've followed everything correctly, there is really no 100% safe way to connect a serial pair to the SPC port without the diode.

If Hitec are going to offer the SPC option and encourage people to connect packs to it then it really needs to be reasonably foolproof and but for the missing diode it could have been.

Sadly as the port is limited to 8S maximum, anyone using 10s or 12s is going to try to connect one of the packs with potentially expensive consequences.

If this can't be fixed, at least there should be a warning in the manual.
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Old 09-20-2010, 12:27 AM   #292 (permalink)
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I definitely agree about putting the warning in the manual when using spc and series connection. I hope that hitec up the maximum voltage of the receiver SPC to at least 14S on the next generation receiver. I dont think that would be too hard as they will just have to regulate the higher voltage to lower to power the receiver but still show the measure spc voltage prior to regulating the voltage.

Hitec is probably working on an add on module for the telemetry sensor station that will also measure voltage, amperage draw, min max voltage, watts, etc.. They have already rpm, fuel sensor and such; I think its just a matter of time.

But for now I am happy with the diode until they do something next. If I am really paranoid about the diode I can just use 2 diodes and 2 positive wires going to the spc but I dont think I need that. I am sure that my thumbs will crash the heli first before that diode goes out.

If I have time in the next month I will work on the redundancy system and let everyone know how that works out.
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Old 09-20-2010, 01:22 AM   #293 (permalink)
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Well I for one appreciate your help Dxflyer. You to Bob for drumming up all the chatter on this. I'm going to power my SPC port from the serial cable I use to hook the two lipos up. It will be off the negative side of course.

So the diode band goes towards the rx correct?

I'd be very interested in a redundancy system if you come up with something.
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Old 09-20-2010, 02:33 AM   #294 (permalink)
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there is no design oversight, the SPC works fine if you plug a pack directly into it up to 8S, which is what it was designed to handle.

I'm guessing that, eventually the telemetry station will have voltage sensing apparatus that will be used for greater than 35v, and that would be the appropriate and well-engineered solution to the question of telemetry on 9s+ setups... whenever they release it.

Last edited by DannyZRC; 09-20-2010 at 12:58 PM..
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Old 09-20-2010, 03:44 AM   #295 (permalink)
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Do you have a link to the telemetry station with the voltage sensing apparatus?
I actually had a Optima 7 burn out in flight with a 8S pack in the SPC port so I'm really wondering if a 8S lipo is a good idea plugged into the SPC port. Hitec has my RX to see what happened.

Quote:
Originally Posted by DannyZRC View Post
there is no design oversight, the SPC works fine if you plug a pack directly into it up to 8S, which is what it was designed to handle.

I'm guessing that the telemetry station and it's voltage sensing apparatus can be used for greater than 35v, and that would be the appropriate and well-engineered solution to the question of telemetry on 9s+ setups.

;P
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Old 09-20-2010, 11:09 AM   #296 (permalink)
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This what you have in the Optima Rx as the power source.



The switch mode voltage regulator IC will be damaged if a reverse polarity voltage is applied.

Two Lipo packs will NOT have the exact same voltage. When you connect a Lipo up to the ESC the capacitor across the ESC input will for a very brief moment be a short circuit that is why you get a fat spark. If the Rx is across the Lipo pack that has a slightly lower voltage to the other Lipo pack then the Rx will be subjected to a reverse polarity voltage for a very brief moment, which will damage the voltage regulator IC.

Having a diode in series with the Rx as per Dxflyer is the correct solution. If a silicon diode is used then there will be about 0.6V drop so adjust trigger alarm voltage accordingly.

Here is a data sheet to a similar voltage regulator IC as used in the Optima Rx’s. I am unable to find the data sheet for the voltage regulator IC that the Optima Rx’s use.

http://www.linear.com/pc/productDeta...eaturesSection

Last edited by Finless; 09-20-2010 at 11:54 AM.. Reason: reduced image size
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Old 09-20-2010, 12:01 PM   #297 (permalink)
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Cool thanks for the info. I was also concerned and asked over on RCG about the big SPARK that occurs when plugging in a ESC when the caps charge up. With this thing not having a reverse protection I could see exactly what you are saying.

Any idea on the optimal diode to use? Amp rating? etc?

Bob
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Old 09-20-2010, 12:58 PM   #298 (permalink)
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Quote:
Originally Posted by maarset View Post
Do you have a link to the telemetry station with the voltage sensing apparatus?
I actually had a Optima 7 burn out in flight with a 8S pack in the SPC port so I'm really wondering if a 8S lipo is a good idea plugged into the SPC port. Hitec has my RX to see what happened.
too much radio jumble rattling around in my head. I assumed the A9 had separate voltage sensing apparatus since the DX8 does.

my bad :*(

I adjusted the wording on my post

it's also disconcerting that you experienced trouble with an 8S setup. hopefully a fluke.
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Old 09-20-2010, 01:47 PM   #299 (permalink)
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Yah I hope that was a fluke. But to play it safe, I started trying to just use one of the packs to supply the SPC.

I hope hitec comes out with some battery orientated telemetry sensors. A sensor that measures MAH usage would be the ultimate.
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Old 09-20-2010, 09:28 PM   #300 (permalink)
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Quote:
Originally Posted by DannyZRC View Post
there is no design oversight, the SPC works fine if you plug a pack directly into it up to 8S, which is what it was designed to
How many people actually run a single 8S pack?

Most people I know run 2x4S so even within the design limit you run the same risk of damaging the RX with a reverse polarity voltage. This is why I would say the absence of a diode to prevent this is at least a design weakness, even if you prefer not to characterize it as a fault.

The very least we need is a warning about using serial packs with the SPC port in the manual.

Adding a voltage sensor with a higher range to the sensor station would also be a great addition.
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