Here is the new Multicell monitor from SLK Electronics in the USA

 see: www.slkelectronics.com

 where you can order the unit and other bits as well. at very sensible prices.   Sid has emailed me today to say a MM7  has been posted.   ( I think he has been ill, hence  the two week silence from me)

There is a PDF manual on the website which explains how two units can be connected for larger, or multiple pack monitoring can be arranged.  As I only have 2 X 3 cells (=6) I can connect the balance  plugs via a special Y adapter (available from UH) . Therefore I only require the one unit for the B25 at the moment.

With regard to the Graupner DPM, when I get a chance, I will send it back under warranty to Gliders in Newark for a replacement. I am not confident about using it though.   

I have one B25 wing virtually finished, and the other one is started.  Tail servos are all in and set up. There are two micro servos on the rudders and one 12kg all-metal servo with 3mm linkage to the brass elevator horn. 

A RESULT AT LAST!!!

 I spoke again to Peter at Gliders Distribution. They handle Graupner products. We talked at length about the discharge module I had no luck with. 

Finally the truth is dawning!   The Graupner Discharge Protection module (DPM) does not pass reciever signal return to the ESC contol circuit.

So I hot wired the ESC with 4.8 volts(on the throttle cable ) and it now does actually work,  but I feel it is not really a viable solution as there may be unforseen problems  

BUT

Graupner now have a NEW version of their DPM     It is the business!  All in a neat case an sprouting no less than TWO jumpers and choice of TWO lipo cutoff levels (2.5 or3 Volts. 

The jumpers allow for BEC pass through AND, the all important bit, opto power supply for ESC's that need it.

The unit will monitor up to SEVEN CELLS from TWO batteries - thats 56 VOLTS   for goodness sake!

I spotted this new product on Graupner's website and called Gliders to order one. Peter called after a few days to say it was now in stock. The credit card was out faster than John Wayne could draw. A measly £20 quid and a couple more days and it was in my hands

 Neat Huh!

I

I set up the full, and closed, throttle endpoints. I have two 5000ma 11.2V packs wired in series to the two motors. The ESC's are programmed for Low volt cutoff (2.4Volt) and the Graupner DPM is programmed to cut at 3 volts. This way, it is the DPM that will always cut the throttle pulse to BOTH motors (via the Y lead)

I set the system up to run. The DPM signals, by LED's, the total number of cells in both batteries and now passes the throttle signal to the two Esc's The final plug on the main battery pack was plugged in.The motors went through their Audible tone responses, and gave the final 'Tada' I moved the throttle trim up and both motors fired up together almost to a beat.

As this is a bit of a 'lash-up' I am not able to do extended high power runs yet. So I had to be content with pulling just one of the Lipo balance plugs out of the Graupner DPM (that would be three cells gone seriously bad rather quickly, if you see what I mean)

Both motors immediately shut down together, despite their main battery connectors still being intact.

'RESULT!'

. This is ,of course the whole point of tmy setup. So no 'Death rolls' can occur

There is one common battery supply. Both BEC's are disabled.

below is a small part of the schematic wiring diagram supplied in the Graupner manual for the DPM

see here

I now need to complete the second wing on the B25 before I can do a full power run on both motors and test the DPM all the way down to a 'real' 'Low Cell' scenario

This time it will work

Hi Chris

The Graupner unit allows for BEC option which can be set on or off.

I would always use a separate RX battery. The Graupner unit allows the throttle signal through with no problems even with opto coupled ESC's.

It is a very flexible unit and is a 'no brainer' at the price 

I look forward to hearing that it will actually work as required, with both ESCs and 2 x batteries, in a real world test as it were ! Meaning, as you put it, in the scenario where the unit monitors both packs, and all individual cells, and pulses /stops BOTH motors exactly in synch several times over in testing. The graupner graphic of course only refers to a single ESC and thats where things get interesting...Y lead 2 x escs together and lets see. I know you have done a simple "pull out one balance plug" test....but, heres hoping

Good luck, and well done , please keep updating us

 Power test BOTH motors 

I have now  bench run my set up till the LIPO's were exhausted.  This was a single pack comprising two X 3S, 5000ma delivering @22V to my two

TURNIGY 50-65A 400kv Outrunners  with two TURNIGY Plush 80A  Speed Controllers

 The setup was calibrated using the ESC programming card, selecting soft start, and the cut off set to 'LOW' (2.5V).  The throttle end points are set using the transmitter. 

I am using the Futaba 2.4GHZ equipment. The throttle trim is electronic, and you have to ensure it is closed down before attempting to start the motors. (otherwise the ESC's won't sing the 'all ready ' tones).

The trim is advanced till the idle is initiated. The close matching of the Turnigy  ESC / motor combination, means  that they start pretty well together.  NICE

The Graupner DPM was set to 'No BEC' and cut off at 3Volts.

I then spent a chilly while with two  13 X 10 props whirling away  for what seemed like ages. I also had a wattmeter in circuit. I couldn't go to quite full power for long (Too blooming freezing in the workshop!!)

The wattmeter showed I had run over 4000ma out the pack, when I detected the first signs of termination. The motors lost a little power, both together, The symptom was a bit like my old lawnmower when its nearly out of petrol!

The LED's on the Graupner DPM  flickered quite a bit as the throttle signal was cut back on both motors. This causes the pack voltage to recover a little. All the time both motors were reacting in an identical manner. Eventually they stuttered and slowed, both in complete unison. 

At this point the LIPO's were well and truly exhausted. I disconnected the pack and checked them with a CELLMETER. You could see which cell had got to 3Volts. (Pack 3, cell 2 if you want to know) 

My packs are well balanced, The other cells were very close to the minimum. I put them on the chargers and they charged back up quite happily in 75mins.

I have a very good feeling about this. In flight, I will try to land with some juice left, but its very comforting to know that I will be safe from a one motor failure situation.

Graupner have a real winner with the latest LIPO protection unit. It also has unrivalled capacity for very large setups, where individfual cells will be more at risk. I shall be fitting one of these to my TopGun Spit asap.

I have a VISIO drawn PDF of the wiring arrangement, together with notes if anyone want to see it 

Well done Peter and yes please post the PDF

Martyn 

Ditto ( and the visio file please ) although I think I can visualise it all. I will PM you so you have my email addy

Ahhh, you havent entered your details for PMs on your profile page

You cold try a zip version of the file that might attach to a regular posting or convert the fie to a  jpeg?

Hi Guys

lets see how this looks

I just downloaded it for a looksee

Its a bit fuzzy on the text

I thought my profile gave an email address?  Cos I had a coupla PM a while back.  

Yes it does now

I notice on the diagram they suggest an isolator switch in the pos line of the batteries. I presume that if you wanted to use two sepaerate batteries ( one for each motor )  the  issue is that maybe the internal circuitry of the DPM would effectively connect the two batteries in parallel via the balance leads which are obviously the monitoring method ? 

'They' dont suggest anything.

This is my preferred 'elf an safety requirement .  I do not like fiddling about with a 'live' model, especially as I have to 'flip' the model over onto its wheels after connecting up the packs.

The VOLTAGE LEVELS are what is monitored by the Graupner DPM, through the balance taps (in exactly the same way as a decent balance charger would monitor each cell in a pack)

CURRENT only flows out of the main  Lipo barrery terminals . The Graupner unit is not bothered whether you connect the main battery terminals in series or parallel.

You could also ,for example, have two 3 cell 5000ma packs connecting their balance taps by a special Y lead (they sell em at UH) to one side of GDPM and the same on the other. The battery terminals could then be configured in a series/parallel combination to provide one big 10,000ma 22Volt pack for the Mitchell.

You should only operate with one common battery pack for all motors on a multi-engine model. (Sez Castle Creations)  

Drawing available on request   

Peter - the B-25 looked superb flying by at the Horizon event this week, (see the front page article)  we were very impressed.

Perhaps you get a party hat & whistle.

I didn't with mine

I recon to use 4 X  3S  X 4000ma  packs on two 'Y' leads nto the cell monitoring connections on the Graupner DPM. Twenty five quid each at UH.

An old mate of mine, John Greenfield of the LMA gave me a 'heads up' over the 12kg servos I'm using.

At 'stall' on 6Volts they draw @ 2 amps each. I have 5 in the system. Thinks I'll use a couple of A123 cells-which should handle the peak currents.

Also need a power distributor as I wouldnt want to put that kind of load through the reciever connectors. 

Hi Peter,

Can you tell me what you use as an isolator switch? I am looking at using 2 x 6s packs in series in my latest project and like you, will have to turn the model over as well as attaching the wing after connecting the pack....much rather not do this while "live"!

Cheers

 Steve

Its a little large. I cut off the key and cut a slot in the shaft. I also cut the studs off to a single nut.

I already got one in my Topgun Spit.  You need two plated lugs and a serious soldering iron with a large surface area bit. The lugs can also be 'crimped'- with an £80.00 crimper!  

You can turn the 'key stub' quite easily with a screwdriver. I made a hole in the 'fus' smaller than the key shaft. This has the added benefit of retaining the switch bit. (It also prevents my annoying mates from nicking it!)

There are a few flavours out there starting at @ £6.00 (ebay)

Theoretical ratings are 100AMPS at 12Volts. I am running 36volts on the Spit at around 40-50Amps.

Greg Covey who runs 'Amped' at RCU in the States swears by them.

I personally think some sort of device should be compulsory. on the grounds of 'Elf & Safety'

. On smaller models, something like a Deans plug with a  thick copper bar soldered across it would work, if you can find a way to secure a socket in the fuselage side wall.

Crikey thats a car battery isolator switch !

As a geek friend of mine said,

'with these kind of batteries and current draw, this is mini electric fork lift truck technology' !!!

He agrees with me that some sort of mechanical, externally accessible, isolator device/switch should be employed.

Imagine if a fault developed in an ESC and your unrestrained model ran into someones child- or anyone else for that matter.

An aircraft with its batteries connected is just as potentially dangerous as a running 'glow motor. You could ,in a lapse of concentration,, accidentally catch your hand on the throttle stick.

I personally think an electric motor that is 'live' but not turning is more dangerous as there is no noise to make you aware of the dangers .

I used to be technical design manager for an industrial electronic company. We had transistor controlled high voltage systems using ESC technology on a much larger scale. My colleague in the service department wanted re-assurance that all products would have a manual isolator switch in case the electronic control circuit jammed on.

Nothing new about this then.