ChuckC

My Feedback: (24)

We're still researching JR's voltage drop issue. I decided to draw it out since it's much easier to understand that way and I think this will help. Interesting to note, though that the 3-poled Hitec 625 MG servos draw so much current when rapidly moved. This actually makes sence though, since it takes more EMF to get them off zero than would a coreless or 5 pole motor-especially when they're asked to oscillate rapidly back and forth. But still, at absolute max 3 amp draw, with the given batteries, why should the voltage drop enough to both red line the receiver and drop out the turbine ECU?

mr_matt

My Feedback: (10)

Have you got a 6v NiMH and a 4.8 V NiCad hooked to the same buss? I assume the little rectangle to the left that everything is hooked to is the receiver bus?

patf

My Feedback: (4)

that really is a problem, not sure if it is affecting your numbers or not, but the 6v pack is essentially trying to charge the 4.8 pack through the receiver along with all the other stuff going on.

ChuckC

My Feedback: (24)

Could be the goolash of batteries is an issue, but to recap:

1) Neither battery independently can supply enough amperage to prevent the voltmeter from going red (just uplugged each)
2) The 6 volt is regulated mith a minihobby regulator
3) Yes, the series of rectangles represents the receiver plugs/buss.
4) I didn't realize it when I was looking at the wiring at first, but the 4.8 volt battery is actually Y-ed in with the meter.
5) The 2nd, in-line ammeter was used to measure amps in line between the batteries (total draw) and each individual servo. Come to think of it, we must have only either measured 3 amps off one battery adn had the other battery disconnected or only measured the draw off one battery with the other still connected...JR do you remember???

I kind of find it strange that neither battery can't provide 1-2 times it's rated capacity for a very short period of time-one battery is brand new (I think the 4.8).

Tom Antlfinger

My Feedback: (24)

Running a 4 cell pack and a 5 cell pack really should not cause the problem.....even with a dead flat 4.8 pack and a fully charged 6.0 pack, the internal resistance of the 4.8 pack will block most current flow.....thats why our chargers have to run at least 8 volts on a 4 cell pack and 9 volts on a 5 cell pack initially to get any electrons moving....I run dual 5-cell batteries on most of my planes and often forget to charge one of them.....one may be at 6.4 fully charged off the charger and the other one at 4.8-5.0, almost discharged completely....no problem.....

Something else weird in Chuck's setup, either both batteies have at least one bad cell, or something is drawing current big time......

I just had to change out one of the elevator 8411s on my Bandit......still worked , but got hot just sitting at idle...could smell it.....measured current.....good side 8411......60ma at idle......bad side 8411......235ma at idle.......still haven't figured that one out......

Tom

ChuckC

My Feedback: (24)

If JR and I measured the amperage accross only one battery, then the real buss amperage on his set up could actually momentarily see 6 amps, that is if each servo were to draw or original figure of .3 to .7 amps.

Our next step is to try different servos and battery packs-the packs may be the issue.

A regular SCR 1400 4.8 volt battery pack SHOULD be able to power this thing, right? I have an SR batteries pack of that type brand new, so it should do the trick-theoretically. Time to also start eliminating components I guess.

mr_matt

My Feedback: (10)

It would be nice to watch the ECU supply voltage (right next to the ECU) with a storage scope. A pulse much sharter than what you can measure with a DVM could be doing it.

What ECU is it again?

ChuckC

My Feedback: (24)

It's a RAM 750 plus.

Figures-I dumped a couple (about 6) lab grade oscilliscopes for next to nothing (what am I going to do with these???) along with about 25 to 30 DVM's and a pick-up load of other misc. electronics. But, you know, better to be on this side than the pack rat side-that my dad was on...

Yeah, we need to be sure we're watching the total buss voltage available to the ecu, which would be simple enough with the in-line ammeter-if it responds fast enough. The other voltmeter responds fast enough, but I don't know about the Hanger 9 ammeter.

jetpilot

My Feedback: (48)

I crashed my Kingcat Recently from what I concurred was battery failure.
I just installed a smoke pump in a centerline tank. I installed the pump and battery all in the small compartment up front. The exposed board wore down the power lead, going in and out, during the setup. I replaced the lead that was worn and inadvertantly replaced 2 wires with 3. This plugged into the reciever, acted as another power source along with the 4 cell 4000MAH 7.4volt duralite. The smoke pump had a very low MAH 4 cell pack. Both batteries were freshly charged. Needless to say the airplane crashed from what i believed was the smaller battery killing the larger and trying to power my high current draw servos.
Scott

Tom Antlfinger

My Feedback: (24)

Well, I stand corrected on one of my assumptions after a test.....Using fully charged SR 5 cell and SR 4 cell, 2200 packs, which actually cycle to 2800maH..... I hooked them both into a 950S RX....I inserted a Hangar 9 Volt/Ammeter in the line to the 5 cell pack.....

Findings:

1. There is significant current flow from the 5 cell to the 4 cell of 1.57 amps...both packs fully charged........

2. I then substituted a 4 Cell/600maH pack, also fully charged.....also about 1.5 amps from the 5 to the 4 cell pack, indicated by the (-) reading on the ammeter

3. I then hooked up (4) 8411s and cycled them all as fast as I could, but with no load on the servos.....Current went up an addional 1.2 amps, about 300-400ma/servo.....at no time did the voltage drop significantly....started out with battery only at 6.47 on the 5 cell pack, and 5.19 on the 4 cell.....during the test with both batts on the bus, voltage never dropped below 6.30 volts....

So, there can be a significant additional current draw, but only about 1.5 amps max with fully charged packs.....that is still not enough to explain Chuck's problem, as the bus voltage in my setup never drops low enough to be of concern....although I have not looked at it on a scope.....

Not sure it caused Scott's problem either, as he started out with both packs fully charged and the loss occured fairly early into the flight if I remember correctly.....still should have had allot of juice left on a 4000maH Duralite, even if it was cross-charging the small nicad.....

Without seeing exactly how he had it mis-wired, it remains a mystery to me.....


Tom

jetpilot

My Feedback: (48)

Duralites might be the difference.
A 4 cell Duralite 7.4 volt 4000mah would not start my BMT. The Duralite would get spiked too hard all the way down to 3v and not let the BMT start. Im sure that the little battery along with all the 11 servos was too much in the turn with elevators and ailerons input applied.
Or it could of been a conspiracy!!!
Scott

bcovish

My Feedback: (8)

I have a question. One person says I'm wrong and another says I'm right

I'm running two 1800 6V packs, each pack has it's own switch and voltage regulator (Mini Hobbies) and then each plugged into the receiver.

I'm not a genious when it comes to things like this, so if I need to do something else, please keep it simple.

Thanks

Tom Antlfinger

My Feedback: (24)

Bob:

That's what allot of Giant Scale guys in our club run, some with one RX, and others with 2 RX ....I'm not sure what regulators they are running though.....somewhere someone posted a while back that Tony Tehan did not recommend paralleling 2 regulators like that into one common RX bus......I never personally heard Tony say that myself.....so it may just be an incorrect recommendation, for all I know.....

At Lake Wales last year, I did ask him about using his regulator for Lithiums......he said don't do it......he said the input was designed for 6.5-6.8v maximum input, typical of a 5 cell pack coming off a charger with a surface charge, and not for the 8.4v that Liths come off the charger.....he said if you started drawing allot of current, it could overheat, so for Liths I use either the Duralite or Powerflite regulators or the new Regulators Andy Lo has that are good for up to 15v on the input side.....

Tom

mr_matt

My Feedback: (10)

I use that same set up Bob, but not with those regulators. I use Jim Oddino's. THey are OK to hook up in parallel. I do not know about the MiniHobby units. I know that the original Duralite regulators had a not specifically telling you NOT to hook them up in parallel. I would ask Antonio.

Tom Antlfinger

My Feedback: (24)

By the way Bob, that's what is in my KingCat for the RX and Servos, but I am using a couple of Andy Lo's new regulators which output at 5.5v with input up to 15v, and I am using a Duralite for cranking the P-160.....I have a Powerflite 7.4/4800maH pack coming which I will stick in, if and when I get it.....been backordered....

In my Bandit, I have (2) 1800 5 cell packs, AA size, not sub-C.....these go into one of Andy Lo's Battery Backers which has 2 inputs but only one output to the battery slot on the RX....the nice thing about it is that it has an internal 0.9v drop, so you don't have to use regulators, and overall, it is smaller than 2 regulators, which is a definite consideration when wiring up an old Comp Bandit.....it balances the draw on the batteries, so they discharge with essentially identical curves...

Tom

bcovish

My Feedback: (8)

Tony is the one who said it was OK to use it that, but told another person here in Austin not to use it that way. Will call Tony tomorrow and check with him again.

Thanks guys,

jetflyer

My Feedback: (5)

Just like to say thanks again for all the suggestions and for Chuck making a diagram of my system. Been busy with work, but I am going to try and get a video on my setup and actual readings that I am seeing.

So far though, as long as I have both battery packs on, the bus voltage does not drop into the red zone on the Hobbico voltage watch. It stays well into the safe to fly zone.

JR Gautreaux

Mace

My Feedback: (21)

I saw a mention of (Andy Lo's Battery Backers) in your post and would like to know where I might find one for my bandit as well.

Thank You,

Mace

Gary Jefferson

My Feedback: (167)

Bob, I am running the same setup that you have which is two JR 1800ma 6 cell packs. Each pack has its own JR switch (w/built-in charge jack-the expensive ones) and a Mini Hobby regulator. So that is two batteries, two switches, and two regulators. One is plugged into the battery port of my receiver and the other is plugged into an auxilliary port.

I have been running this setup for the last three seasons in three different jets and it works great. When slow charging I charge both packs at the same time on my ACE charger and when fast charging I charge one pack at a time. I can't remember why for sure but it seems like the second charger will shut off when trying to fast charge both at the same time. Gary

bcovish

My Feedback: (8)

Thanks Gary

That's my setup exactly. Although when I charge, I charge directly to the battery. Disconnect them before the switch.

seanreit

My Feedback: (60)

Let me clear this up as I'm the guy that spoke to Tony!!

First conversation I had with him he told me not to do it. So I started preaching that gospel.

I have a lot of respect for Tony, but after getting a bunch of (let's call it) Feedback here, I decided to grill Tony.

So I went up to him at one of the meets and said "Tony, let's get real, why are you saying not to put to regulators on the same receiver".

His response (and this is no BS):

"I don't want anyone out there to think that they are getting more capacity than the two batteries they have connected". It was then that I came to the same conclusion you all are coming to right now by reading this. And for anyone that possibly thinks that I'm making that statement up, I walked right over to Todd Whitkoff and told him what I had just heard.

Guys, there is absolutely no technical reason not to put the two minihobbies onto the same bus. Obviously, if it was a flawed setup, so many people here would have found the problem in it. I know several people that have run and are running this setup.

FYI, I posted a very similar post to this one very soon after I "learned" what I was dealing with.

Hope this clears up this issue again.

Sean Reitmeyer