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| Reading high currents on PCB: Hall effect sensor vs shunt resistor |
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| ejeffrey:
Here's one for a dollar in small quantity. https://www.digikey.com/product-detail/en/te-connectivity-passive-product/TLR3A30ER00075FTDG/A131798CT-ND/8603928 There are a lot more options if you pick 1 mohm or 500 uohm. 50 amp is a lot but not unreasonable. 2oz copper on top and bottom with wide traces and lots of vias and you should be fine. Still an external shunt may be an easier option. |
| Jeroen3:
50 Amp is territory for LEM sensor modules. Where you can just feed a wire trough a ct. Or Sensitec, but unfortunately they obsoleted the integrated solution, CMS3050, but if you can still get a few... They're amazing! Zero drift spot-on accuracy, good resolution (1/1000th of range, no external magnetic influence. Else just get a piece of wire as shunt and calibrate it. Just like they do in those high current power supplies. There's a teardown on the channel somewhere of a high current power supply, but I can't find it... |
| superKris:
--- Quote from: Vovk_Z on May 06, 2020, 11:25:00 pm --- --- Quote from: superKris on May 06, 2020, 06:57:13 pm ---However, like I wrote i fear about the dissipation that will come with that. I'm hoping to run 40A (with peaks of 50) trough a PCB with 2oz copper "traces" on both sides. Below you can find a drawing of what it currently looks like. Its a automotive application (RV) so temperatures can get high easily. --- End quote --- --- Quote from: superKris on May 06, 2020, 06:57:13 pm ---I was only able to find this SMD type, but i dont really understand how this would work on the suggested 20oz board at 50A. Even with a shitload of vias... Wil it hold the current? --- End quote --- You may divide one shunt into several parallels. But is there a strong need to put shunts onto the PCB? 40-50 Amps looks good for external shunts. --- End quote --- Thank you, i was struggling a bit with putting shunt parallel. Ohms law tells me that with equal resistors in parallel the current must be the same. However i can remember reading some articles about current always taking the path of least resistance, so i can imagine that even the slightest imbalance might cause the current to flow trough the lowest shunt. Anyway, a external shunt is out off the questions. The whole idea is that i want tot move a lot of loose components like relays, fuses, and current sensors. --- Quote from: ejeffrey on May 07, 2020, 01:49:24 am ---Here's one for a dollar in small quantity. https://www.digikey.com/product-detail/en/te-connectivity-passive-product/TLR3A30ER00075FTDG/A131798CT-ND/8603928 There are a lot more options if you pick 1 mohm or 500 uohm. 50 amp is a lot but not unreasonable. 2oz copper on top and bottom with wide traces and lots of vias and you should be fine. Still an external shunt may be an easier option. --- End quote --- Thanks. I guess 500uohm could work, but i can imagine the output would be very sensitive! 0,1A would be 0,50uV. I hope a INA219 would be up to this. I guess its mV vs dissipation. Anyway, i'm having a little trouble imagining the physics of 50A running trough such a small SMD component. I guess i could take 2 of 1,5mOhm and put them parallel on both sides of the PCB, but that is still a very small pad its sitting on! My mind says i need huge thick trough hole shunts to pass that amount of current.... --- Quote from: Jeroen3 on May 07, 2020, 06:16:00 am ---50 Amp is territory for LEM sensor modules. Where you can just feed a wire trough a ct. Or Sensitec, but unfortunately they obsoleted the integrated solution, CMS3050, but if you can still get a few... They're amazing! Zero drift spot-on accuracy, good resolution (1/1000th of range, no external magnetic influence. Else just get a piece of wire as shunt and calibrate it. Just like they do in those high current power supplies. There's a teardown on the channel somewhere of a high current power supply, but I can't find it... --- End quote --- Isnt that more or less what i'm already using? Anyway, such current transducers are expensive, large, and not as easy to mount. No problem for a single build, but i'm hoping to sell the product or give away the disign for free in a later stage. Thats sensitec looks great, but i cant find any sellers, and it looks kinda expensive. I think i have seen that video. I think shunt like those might be suitable, but they are not available in low quantities, or the price goes up to € 10,- which i think is ridicules |
| fcb:
So we use 20ppm/oC tempco current shunts in our compact power analysers (CPA) and we derate them ALOT to get stability over current range - HOWEVER if you can afford a few % error and a factory calibration cycle then why not use the actual PCB traces as the current shunts - you will likely need a bit more accuracy than the tempco of the copper PCB will allow (4000ppm/oC!) - you can measure the actual temperature of the shunt (MCP9701) and apply tabled compensation (which would easily get you under a few %). |
| exe:
--- Quote from: superKris on May 07, 2020, 09:37:33 am ---Thank you, i was struggling a bit with putting shunt parallel. Ohms law tells me that with equal resistors in parallel the current must be the same. However i can remember reading some articles about current always taking the path of least resistance --- End quote --- No, not at all :). They may not equally share the load, but this doesn't mean they don't share it at all. A random article from the Internet: https://www.electronics-tutorials.ws/resistor/res_4.html . Basically, since resistors are in parallel, voltage accross them is identical. So, they share currents as following: 1/Itot = 1/Ir1 + 1/Ir2. You need to route kelvin connection to them, may be add small resistors in series with sense leads (in case one shunt goes open and current may decide to flow through sense leads, not sure about that, what's your opinion?). |
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