# Transforming incoming Channel Values without needing a traditional rule **URL:** \ **Category:** Tutorials & Examples\ **Tags:** rules, alternatives\ **Created:** [July 17, 2026, 1:01pm UTC](https://community.openhab.org/t/transforming-incoming-channel-values-without-needing-a-traditional-rule/169820 "2026-07-17T13:01:22Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![BrettLHolmes](https://community.openhab.org/user_avatar/community.openhab.org/brettlholmes/32/105286_2.png) [@BrettLHolmes](https://community.openhab.org/u/BrettLHolmes)\ **Post date:** [July 17, 2026, 1:01pm UTC](https://community.openhab.org/t/transforming-incoming-channel-values-without-needing-a-traditional-rule/169820/1 "2026-07-17T13:01:22Z")
Hi All I know everyone has a lot going on with the new releases but thought i would take a quick moment to show a feature that I am sure many people have seen but will create a rule to handle (I almost did) So this is just a callout to all the people who continuously provide us such a flexible system and if i could do anything better (including writing this tutorial better please let me know) I have a scenario where there are 2 inverters primary and secondary - the secondary inverter actually just feeds everything it has to the house power line (well actually to the primary inverter ) and if there is insufficient demand that primary inverter will send to the batteries if needed. Just for clarity the primary and secondary inverters are actually a group of 3 inverters with 120Kwh of Batteries attached - yes a big installation) the challenge - how to know what the real consumption is if it is not just the Sum of the two inverters) In this case there is a Smart Meter (an EM2 with Tasmota software but not 100% relevant) and this meter measures the the power and when it goes to the inverter (insufficient demand ) the value goes negative - how to handle that First thought - Easy create a rule on update to EM2\_power0 and when its negative update the new Item (i called it c\_inverterFeedbackFlow) with the negative value and include that Item in whichever group is needed - actually turned out to be far simpler - I created a new Item and linked it to the Power0 of the EM2 and when I went to link it and choose the SCRIPT Ruby Profile i added this ruby script to the “Thing to Item Transformation” ```ruby |(input = input.to_f) > 0 ? 0 : input ``` Basically it says if the value is greater than 0 set the Item(c\_inverterFeedbackFlow) to 0 or if its negative make it the value of the Channel. I just add that new Item to the group for the Consumption calculation and I can also show the item it separately in the UI as needed - no need to have a rule triggered every time the field is updated. Using the “NEW” YAML Copy option here is the complete Item Definition ```yaml version: 1 items: c_inverterFeedbackFlow: type: Number dimension: Power label: This is the Feedback from the Kostal to the Outback(W) format: JS(config:js:hasThousandToK):%s unit: W groups: - g_kostal_AC_Power_Total - g_TotalPower channels: mqtt:topic:a5958ecfef:9f24bd3e63:Power0: profile: transform:RB toItemScript: "|(input = input.to_f) > 0 ? 0 : input" e ``` ![image](https://community-openhab-org.s3.dualstack.eu-central-1.amazonaws.com/original/3X/8/7/87e2e491a7b4dd160957a386afd303dc47d50ae7.png) c\_inverterFeedbackFlow ---
**Author:** ![rlkoshak](https://community.openhab.org/user_avatar/community.openhab.org/rlkoshak/32/75251_2.png) [@rlkoshak](https://community.openhab.org/u/rlkoshak)\ **Post date:** [July 17, 2026, 3:16pm UTC](https://community.openhab.org/t/transforming-incoming-channel-values-without-needing-a-traditional-rule/169820/2 "2026-07-17T15:16:07Z")
Thanks for posting! It’s always great to see new tutorials. > [@BrettLHolmes](#): > > no need to have a rule triggered every time the field is updated. Just note that this doesn’t make the transformation any more effecient than doing this in a rule. The script engine still needs to process the jRuby code. But it is a bit more stramlined and ends up creating fewer events on the event bus as it runs between the Channel update and the Item update. So it’s Channel → Transformation → Item instead of Channel → Item → Rule → Item. Some other things you can do with script transformations is pass them arguments. This is more for situations where you create a generic script transformation that would be used across multiple Links instead of an inline. You use URL encoding to pass the arguments when you call the script (e.g. `JS(myTransform.js?arg1=value1)`) and in the script you can use `arg1` same as you use `input`. So you could make a relatively generic script transformation that can be “configured” each time you use it. You can see an example of this on the marketplace, e.g. [Auto scale units](https://community.openhab.org/t/auto-scale-units/162133). Also, as you can see, if you ever do create a transformation like that you’d want to share, you can post them to the marketplace. And others will be able to install them from Add-on store → Transformations. ---
**Author:** ![BrettLHolmes](https://community.openhab.org/user_avatar/community.openhab.org/brettlholmes/32/105286_2.png) [@BrettLHolmes](https://community.openhab.org/u/BrettLHolmes)\ **Post date:** [July 17, 2026, 4:31pm UTC](https://community.openhab.org/t/transforming-incoming-channel-values-without-needing-a-traditional-rule/169820/3 "2026-07-17T16:31:04Z")
@rlkoshak thanks for the advice and comments as always its appreciated ---
**Author:** ![system](https://community-openhab-org.s3-eu-central-1.amazonaws.com/original/2X/6/6a52f2ac5d00e4c7b50471a354b3a9221188be90.png) [@system](https://community.openhab.org/u/system)\ **Post date:** [August 28, 2026, 8:31am UTC](https://community.openhab.org/t/transforming-incoming-channel-values-without-needing-a-traditional-rule/169820/4 "2026-08-28T08:31:10Z")
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