How many AMPS are needed to drive electronics + Motor


#1

I'm pulling .29A with everything sitting idle.

I've connected just one of the ESC through to one of the motors. The moment I activate the motor the entire BB reboots.

My power supply is just a 1A supply which I assume is the problem.

Any quick guide on how many Amps are needed to drive everything?

-Brian


#2

I am going to simply run a battery pack along side the unit for now. But I am still curious about how many Amps the system will pull


#3

there are not yet so many numbers about how much amps the system draws.

this is very dependent on the motor and prop type.

I have all the parts to do a test, but i havent had the time to make a thrust measuring jigg.

I also have diffrent props to see if we can improve the efficiency of the system.

the motors have a certain torque area that they are most efficient in. an overload in torque can cause amp-draws that are very high but not the same increase in thrust.

and user on the homebuildtrovs forum have made a test that shows this very good.

http://www.homebuiltrovs.com/rovforum/viewtopic.php?f=3&t=900&p=4562

i'm going to do the same test with the motors in the kit + a DT700 motor


#4

Hey Brian,

I can't give you an exact number, but you should expect something on the order of 3A nominally on average during normal operation. This seems to be causing some people problems since many alkaline Cs have trouble sourcing that much current and therefore tend to brown out (possibly enough to shut down the BB) when being pushed. We're working on a way to adjust the throttle gain so that when you command the motors, it doesn't rail to full speed, but in the mean time you might experiment with moving the motor slowly using the slide bars in the "diagnostic" tab in OpenROV Cockpit. There also may be an issue with one of the fuses on the Cape which we're looking into, but more on that later.

Also, if you want to get rechargeable batteries, these work great! You can fit 3 into the same tube that 4 alkaline fit into, and if you re-wire the two packs to be in parralell (since they each deliver 11.something volts) you'll have pleaty of current supply to run the ROV without any brownouts. It's kind of an expensive initial buy (~$60 plus shipping) but not having to continually buy primary cells makes it worth it in the long run.

Please let us know if you find out any more about what's going on and we'll do the same for you.

Thank you!

Eric


#5

I am also considering a rechargeable option, and regarding the rechargable cells linked above:

http://www.batteryspace.com/LiMnNi-Rechargeable-26650-Cell-3.7V-4000-mAh-4.0A-rated-14.8Wh.aspx

I'm sure they would work great, but when using such cells (lithium based rechargeables) one should have a protection circuit as well protecting the cells from over-charge/discharge and over-current.


#6

Hello all,

I realize the temptation to incorporate the latest in lithium batt tech and I'm sure there are pros and cons to every batt type, but I cant help but wonder if the old NiCad is the way to go here....qty 10 at 1.2 per cell (longer tubes). Im interested in finding out how the current capacity (watthrs) over time and burst delivery measures up against the alkaline setup. Its not good for any electronics to brown out and I can not help but wonder how we can succesfully test and report anything regarding current draw and performance until we get ahold of the variables (motor model, prop, run time @ throttle setting, batt type etc) ie standardize the test environment. Could we define a standard ROV mission for propulsion and battery test purposes? Eric? Would it be fair to say that Im going to plunk it in the water for 30 minutes and during that time the first 10 minutes Im using the equivelent of heavy thruster bursts of 75% throttle on three thrusters for a 20 second period once every minute (which actually uses more juice than the 200 second total one might think with simple math due to the bursts).....well Im losing my thought process through complication here....I still have 20 minutes to define...arggg. Back to my main thought - NiCads have stable delivery right up to the end of thier capacity (at which time the brown out would be bad for the electronics) but until such time the batteries should work well, they are less fussy about charging, dont mind deep discharge and the temperature (thermal runaway) tendancy shouldnt be a problem if they are kept cool.

Regarding brown outs with the alkalines - A very important part of that test report should include how long and how much work the batteries did before brownout occured...its aweful tempting to run the ROV with your $15 worth of Alkalines in the bathtub for a very fun long while and then suddenly be dissapointed when you realize you need to throw another $15 at it to make it do it again. Its all fine until the dreaded brownout occurs....it will happen with every batt type, some will work better than others (for different reasons), and I think the focus would best be placed on establishing a standard criteria for test, start there and report community findings based on that criteria (everyone using the same / similar work / load / times). Im anticipating doing the NiCad test once I get my ROV...unless someone beats me to it. I wish I knew what kind of batt was in that old philishave elect razor I had for 25 yrs....impressive it was!


#7

Just did a quick test on my bench supply running all the motors in air.

Starting all 3 motors at the same time (forward and up), with the lights off, peaked about 4.5amps @ 12v. Then stabilised at around 3 amps.

I would expect this to peak higher in water with more load on the props.


#8

Long story short- I agree. We've been looking at NiMH batteries which in our observations can source more then 4amps continuously and have the capacity to run the ROV for on the order of 30 mins - an hour (depending on use). Like NiCads, they are easy to charge, reasonably affordable, and fit inside the battery tubes the same way Alkalines do. Even with just 8 (which produces around 10v) everything seems to run just fine. The biggest issue with them really is that they are heaver then alkaline and thus cause the ROV to be heavy in the water (the ROV was designed to be buoyant with Alkaline chemistry). We've also been looking into Lithium batteries that are the same diameter as C cells but are long enough for 3 to fit where 4 normal Cs would go. These are lighter weight, have greater capacity, and deliver more current, but also have a higher voltage so both packs need to be run in paralleled (requiring different wiring then for regular Cs) and they require a balanced charger. As we complete our experimentation, we'll prepare a more formal report, but here is the raw data I took down on my computer during some initial tests with Alkaline and NiMH Cs regarding current draw. Even with preliminary data, I can say that Alkaline's are probably not the best way to go because of their high internal resistance and great cost to replace regularly.

E

3:38PM
idle state
Bench power supply
13.9v at supply, 13.6 on Cockpit display (infiniate current source)
10 sec intervals
0 .32
10 .40
20 .38
30 .38
40 .43 * Booted
50 .42
60 .41
(Stable at .41 without camera)

With camera .488
Peaked at .510

Lights up (idle motors)
.80 (100%)
.65 (50%)


Using Chrome

motors(in air)
1 motor 2.09
2 motor 2.83
3 motor 4.50


lights on idle

Vertical thurster3:36 PM 2/13/2013

100 - 0.81
105 - 1.12
110 - 1.65
115 - 2.23
120 - 3.16
125 - 4.10
130 - 5.05
135 - 6.25
140 - 7.5
145 - 8.7


Connection dies after around 4:55 elaped time
Connection dies at 5:04 elapesd time

With Alk batts

in air
1 motor 1.2A
2 motor 1.9A
3 motor 2.4A


in water
vertical thruster
105 0.90
110 0.93
115 0.94

Current at cut-out
2.8 A (single ESC at 140)

P and S
8.5v, 1.61A - 110 and 70 * Drawing 1.48A (@7.56v) * Died after 3:20min
7.8v, 1.94A - 115 and 65 * Died after 1 min
7.1v, 2.27A - 120 and 60 * Died

NiMH Tests
Idle 9.1v .500A
Lights 100% 8.8v 1.00A
(lights off)

105 0.85A (?V)
110 1.06A (?V)
115 1.3A, 8.5V
120 1.7A, 8.3V
125 2.1A, 8.1v
130 2.6A, 7.8v
135 3.0A, 7.7v
140 3.4A, (?V) *Died

NiMH test2
10.76v and .38A
lights 100% - 10.32v .89A

105 0.87A, 10.3v
110 1.15A, 10.2v
115 1.54A, 10.1v
120 1.97A, 9.81v
125 2.45A, 9.56v
130 3.05A, 9.36v
135 3.66A, 9.03v
140 4.25A, 8.85v
145 4.91A, 8.82v
150 5.40A, 8.60v