Electric Vehicle Isometer - Page 1
Forum section: electronics / projects

author: sanwal209
author_rank: Regular Contributor
timestamp: May 08, 2018, 09:59:23 am
content: Hi Guys,We are trying to build custom isometer which measures the isolation between +ve terminal of HV battery and Chassis also betweeen -ve terminal of HV battery and Chassis.We spent tons of time on looking at commercial available iosmeters specially ISO165C-1 from Bender.So far i figured out that Bender Isometer inject AC signal to the power lines and measure the leakage current which is proportional to the isolation resistance.Following thins is couldn't figure out:1. How to couple 24V excitation source to main high voltage lines2. what could be the excitation source.To be honest this something i could not find any reference design or schematics online. I figured out the block diagram by reading many patents and Studying commercial isometers. If you see any mistake in block diagram please do let me know.Please find the attached Block diagramCheers!

author: Wolfram
author_rank: Frequent Contributor
timestamp: May 08, 2018, 11:26:39 am
content: Sendyne make ASICs for EV isometers, and they also provide a reference design around the ASIChttp://www.sendyne.com/Datasheets/Sendyne%20SIM100%20IC%20Datasheet%20V0.4.pdf. Some of the magic is hidden in the inner workings of the ASIC, but the reference design is a useful starting point.

author: sanwal209
author_rank: Regular Contributor
timestamp: May 08, 2018, 11:32:01 am
content: We are in the middle of validation process for Sendyne SIM100 IC. If it fullfilss what it says in Datasheet then we will go with that one. But we also want to investigate further about how these isometers work.

author: Rerouter
author_rank: Super Contributor
timestamp: May 08, 2018, 12:28:44 pm
content: To me it seems like the same basic functionality as a electricians "Megger", it measures the resistance between 2 wires at various test voltages, and is used to make sure isolation is present between various circuits.

author: max_torque
author_rank: Super Contributor
timestamp: May 08, 2018, 07:22:32 pm
content: Buy one.Yes, you can develop your own, but why? It won't be certified, won't be nearly as robust as the proper item, and you'll be less liable to be pulled up in front of the courts for coporate manslaughter if it all goes wrong!Worth noting, that dynamic (ie near real time) isolation measurement for PWM systems (ie ones with lots of CM noise etc) is a bit of a 'mare and a 'mare than people like Bender have already been through many times before. You won't find much info on how to do it, other than the basic principals, precisely because people have spent a lot of time and money making it work properly.The Bender (or similar) units are not expensive, are fully proven and Insurance Certified.

author: sanwal209
author_rank: Regular Contributor
timestamp: May 15, 2018, 08:38:38 am
content: @max_torque First sorry for late reply, I was on vacations. Yes you are right only if i need it for my personal project. As an OEM we want to have Isometer on our BMS-Master that is why we are trying build our own. Our BMS-Master cost 100Euro in bulk quantity wile bender cost us 300Euro and this doesnt make sense.

author: max_torque
author_rank: Super Contributor
timestamp: May 15, 2018, 05:13:38 pm
content: So, that begs the question why does the off-the-shelf Isometer cost so much money?I can think of two reasons:1) It's development was long and tedious and involved a lot of spending money (on peoples time)2) They are making a fortune of selling these modules for a massive mark up.Given that you can buy a Bender unit, and reverse engineer all the circuitry, and possibly the firmware too, you'll have to make a call as to which you think is the most likely reason for the "high" cost of these units. If you want to sell a device with an integral Isometer, for use on systems above 50vdc, then you will have to think about the necessary validation and certification of that system.Make it too "safe" and there is a danger it won't detect an earth leakage, and you or your company become liable in the event of an accidentMake it too "sensitive" and there is a danger it'll falsely trip, resulting in customer annoyance, recalls and potentially other expensive rework or rectifications.