AMP concerns , how should I test ? - RC Groups
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Nov 10, 2017, 06:29 AM
Ldm
Ldm
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Discussion

AMP concerns , how should I test ?


Hi Fellow RCG members
Question please on a system set up .
I am running a twin motor plane .
1) two 60 size -470 KV eflight motors
2) two Castle 90 Talon ESCs
3) two 6 cell -4500 to 5000 ( on avg ) packs 45 c
I will be running the packs in Parallel,
I want to run the ESCs in parallel and the attached photo of the after marlet adapter makes the ESC connection very easy but ,,,, its only rated for 60 amps max .
Question
Do I need to test each motor for amp draw on the props ?
Test the system as one putting a watt meter in the connections ?
I am not 100% sure on the props at this time but assume I need to select the props to figure the amps ? I may go with three blade and or two . I hope I dont burn the system in the test because I assume that is the only way to determine real amp draw ?
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Nov 10, 2017, 07:56 AM
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scirocco's Avatar
With a given motor and voltage, yes, prop size will determine max current.

To avoid nasty surprises during testing and wasting money on infeasible props, you can estimate the expected maximum current beforehand with an online motor calculator like Ecalc. Ecalc will not be exact, but it will get you close enough to pretty much remove the risk of burning up components in testing - think verification rather than experimentation.

For 2 blade APC-E props the bottom end of the Eflite recommended prop sizes, ie 15x8 should draw about 65A. For 3 blades, 14x9 should stay within burst limits at about 75A. In static testing 10-15 secs should be plenty to verify that current is as expected and that the battery is holding acceptable voltage. At a max of say 75A from a 4500mAh battery, load is only 75/4.5=17C, so you should expect to see a solid 3.7V/cell or better under load with a fully charged battery.

Rather than paralleling the batteries and pulling 2 motors worth of current through a single connector, why not just run each ESC off its own battery?

I don't think you really gain any additional redundancy against asymmetric power with the batteries paralleled as each ESC or motor is still subject to failure. But I do think you increase the risk of total power loss running all power and a lot of it through a single link. Also, if you have a complicated layout physically, choose to lengthen the ESC to motor wires, rather than the battery to ESC wires.

Anyway, whichever way you go, just test a single motor at a time - that will tell you all you need to know about how much current the prop you choose will draw.
Nov 10, 2017, 09:00 AM
Registered User
Especially if you are running big motors like this you need a wattmeter to measure the power consumption statically. I would not use those connectors for this kind of amperage. I would at least use XT60 connectors - and separate ones for each ESC.
Nov 10, 2017, 04:12 PM
Ldm
Ldm
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Scirocco , Volt ,
thanks for the reply .I was originally going to run both packs separately but if you read this months MAN mag the guy that reviewed the plane use a parable set up . He actually made a lot of sense in that why fly electric with two separate motors when you can get perfect better performance if they both draw from the battery's equally .
Think about like this , even if you match the packs , 100% new and charge ect they never ever discharge exactly the same. You can even get different resistance in the line per motor.
Now I can still go separate power and that sounds safer as far as not over loading the system. As far as a motor out vs two motors out , both spell disaster .
Wire length , I wanted the ESCs on the wing for cooling so both have capacatators inline and I checked with Castle for my max length , I am good.
I could make my own X connector for the ESCs with the same gage wire ect and not worry about the connector seen in the pic , but I am not sure why they say this connector is rated max at 60 amps .
Deans has never failed me on 12 cells in a series but many find the deans challenging to solder , that is not me. I have never run a parable system , thought it was a novel idea based on the explanation.
I am leaning towards each system on its own battery as originally planned and my layout could not be more strategic in execution and field assembly . I just wanted to see if some of the exerts ( like you guys ) would provide some advise and I thank you for your valuable imputed
Nov 10, 2017, 05:23 PM
Registered User
I am not saying to not connect the packs together but to use separate connections and higher current ones than the Deans type.
Nov 10, 2017, 08:29 PM
Ldm
Ldm
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So you like the parallel idea you just dont like the Deans and you think the Xt60 can take the amps ?
Nov 10, 2017, 10:23 PM
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Doug Bartley's Avatar
Neither the Deans or XT60 are suitable for running this combo, which may run 75a per motor IMHO
. I use XT60 or anything under 50a. I use the HXT 6mm connectors available from HK for anything over that. You can make a parallel connection from 12ga wire with 6mm ends and be sure they will handle the current. I made up a parallel 10 gauge system for my Dash 8 to run two motors up to 80a each, all with 6mm. Individually they can handle 150a. fwiw Doug B
Nov 11, 2017, 10:58 AM
Ldm
Ldm
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Then why do 6 cell packs 4500 / 40 to 60 c come with the XT60 as stock ?
Also I have run deans on 6 cell and 8 cell zero issues 3 years straight.
Just trying to determine rules vs personal preference.
Nov 12, 2017, 12:28 AM
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Wintr's Avatar
If your flights will average about 6 minutes, you are only drawing about 12C from your battery, which is fairly typical; even if peak current is higher, the connectors are usually limited by average, because of heating. An XT60 or Dean's will handle that just fine, since that is less than 55A on average. If you draw max power most of a flight, as in 3D, then the flights are shorter, since C rates will be higher; in that case, using two batteries, one to each ESC, or going up in connector size (like XT90, APC, or the bullets mentioned above) would be prudent.
Nov 12, 2017, 04:52 AM
Ldm
Ldm
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THanks Wintr
For safety and wanting to use a parallel set up , I will most likely move into a larger set up.
You are 100% correct on your post , many think the XT60 are the end all over deans and they are actually only rated to 65 amps ( 5 amps over deans ) .
I know have pushed deans to 100amps with no issue but not constant .
I will probably end up with the XT 90 only because i cant envision successfully making a short lead with a bullet connector.
I am trying to keep my ESCs lines to the battery withen suggested length so I need my connections to be very short. I am looking at a simple parallel connection for the battery’s and one to both ESCs ( so in essence an X connection. The battery connection for parallel are stock sold for Xt60 and deans, I have not seen short connections for bullets and or xt90 in Parallel .
As far as parallel Esc connections I think I will have to make my own.
I need the ESCs to be on the wing , motor cowls for cooling , so all of those connections with the added capacitors are correct its going to the battery’s for final connection in the fuse that poses my concerns.
Thanks for the advice


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