Current measurement on positive or negative side?

I think the sensor is designed for AC power supplies only and your trying to use it with a DC motor.

no it measures ac or dc, im sure it would work both ways, test it both ways

jonisonvespaa:
no it measures ac or dc, im sure it would work both ways, test it both ways

Thanks for point that out. Once I read the text instead of just looking at the pictures I see it. :blush:

I don't think that the position of the current sensor matters as long as it is in series with the motor. I might place it between ground and the rest of the motor circuit.

Look up Kirchhoff's current law, Current will be the same whatever side you put the sensor, assuming it doesn't branch off at some point. Make sure you put it in series!

Thank You, I thought so, but it's nice to be sure. I'll probably need to read up on my electrical basics :slight_smile:

bloody hell 130a dc be careful with that, i used to work on lifts with very big dc generators scary stuff.

I realize it is counter intuitive But I'd place the sensor in the high side of the motor... because of the possibility of a failure in the power connections to the sensor or the sensor proper. If low side sensing fails then you have full supply voltage on the ground leads.. If high side sensing fails you have no power to the motor, much easier to troubleshoot and much safer to work around. This is one of the reasons why switching grounds is not wise unless it is an absolute last resort -- do-able but inadvisable. Supplies may be switched but it is Always a last resort to switch or sense ground in any high voltage control circuit.
The Allegro ACS series current sensors have a 2KV isolation barrier between sense and sensed conductors so there should be no issues of that nature in using the sensor in the high side of the motor power circuit.

Bob

There is little risk of personal injury, as the system is only 24 volts. But I see your points about troubleshooting and also it makes sense to not have permanent power on ground leads. I will have to find the best compromise between physical layout, possible interference and safety. Thank you.

of my motor (130 amp dc)

as the system is only 24 volts

Does I understand this well? You have a motor that "eat" 130 amps @ 24V :fearful: :fearful:

HugoPT:
Does I understand this well? You have a motor that "eat" 130 amps @ 24V :fearful: :fearful:

If I were to wager a guess I'd say "hydraulic power pack" like jonisonvespaa described. Common on snow plow trucks or dump trailers.

130 amps 24v

what sort of motor is that? im guessing some sort of automotive starter or alternator maby?

Since the sensor is not actually carrying any current, it's not going to have any affect on safety either way in my opinion. It's a hall sensor, meaning it magnetically measures the current in the wire, so circuit isolation is very high.

Is this for some kind of RC car?

afremont:
Since the sensor is not actually carrying any current, it's not going to have any affect on safety either way in my opinion. It's a hall sensor, meaning it magnetically measures the current in the wire, so circuit isolation is very high.

Is this for some kind of RC car?

current does flow through the sensor, on pins 4 and 5 - ip+ and ip-

:blush: Oops, I saw the hall effect verbiage and assumed it to be an inductive pickup. I see that it is actually in series with the circuit, sorry about that. I think I'd look for an inductive pickup sensor if it were me.

The motor is 133 amp 24 volt series wound dc. I don´t know what they where intended for (maybe forklift), but i managed to get hold of 6 of them, maybe 10 years old, but unused. I´m converting a lawn tractor to electric with a motor for drive, and a motor for grass cutters. Arduino is at the heart of the operation. I promise to make a ”bragging” post when the project is finished :slight_smile:

Recently I bought 15 LEM HAL 300 current transformers as surplus from Ebay (the price was Very Right) and one of these devices would be perfect for your application. The device has a 30? mm (approx) hole in it to pass through the main motor current carrying wire. Due to the inherent losses involved in getting the Allegro device soldered in a suitable PCB (4 Oz Cu?) and connections to the controller and battery, a through hole or pass through device is really called for. The HAL 300's can be found for about $50.00... Mine for considerably less (New on Mfr's shipping material). But I see no easy way to get one to you.
The device can be placed anywhere in the motor power leads, hot or ground as it is totally isolated.The LEM device is spec'd from DC to 50 KHz and has an output similar to the Allegro device however it requires a +/- 12 - 15V split supply to bias the Hall effect circuitry. There are available 12 to 15 V isolated switchers that will supply those voltages. Or in short.. I personally don't think that the Allegro device is ideal for your application. My intent here is NOT to sell current transformers but to point out a more suitable device. I intend to make DC transformers by winding a multi-turn primary so I can use them for more reasonable currents... +/- 30 A = 10T primary. Unfortunately.. I had to buy 15 (at less than the single unit surplus price, much less). It just occurred to me that the motor current is likely going to be considerably less than 130 A since your load will be just the mower and batteries, I should think more like 10 - 20 A which is easier to deal with than the rated full load current and entirely do-able with FR4 PCB material (I would use double sided FR4 laminate and have it plated to 4oz/in with a lot of via's stitching the top and copper together).

Bob

afremont:
:blush: Oops, I saw the hall effect verbiage and assumed it to be an inductive pickup. I see that it is actually in series with the circuit, sorry about that. I think I'd look for an inductive pickup sensor if it were me.

hay, dont be sorry just pointing it out

It is still an inductive pickup, just different physics.

Bob

Don't wish to put a dampener on your project but I think some maths need working on.

Your motor rating is only 3kW (4HP) assuming 100% efficiency. This seems far too small for a lawn tractor. Series motors are not constant speed, their speed being dependant on load applied which in turn increases current demand. (theoretical speed, ignoring physical restraints, at zero load is infinite) If from a fork-lift, they were probably used to drive the hydraulic systems which is only intermittent use. In a tractor they will be subject to continuous use and therefore may be prone to overheating. On basis that battery capacity is a pair of 100AH, 12volt units, with an average load of say 100A and limiting depth of discharge to 40% (too much some will say) the duration of running (or should that be crawling) will be a maximum of 24 minutes. Decent batteries are gone to weigh about 25+kg each so there will be a weight change in the tractor of +50kg for batteries and say -15kg for engine, so a net increase in weight of around 30kg.