# How to Calculate Power (P) from Voltage and Current Values in Node-RED?
**URL:** https://discourse.nodered.org/t/how-to-calculate-power-p-from-voltage-and-current-values-in-node-red/86936
**Category:** General
**Tags:** function-node
**Created:** [2 April 2024 11:04 UTC](https://discourse.nodered.org/t/how-to-calculate-power-p-from-voltage-and-current-values-in-node-red/86936 "2024-04-02T11:04:13Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@noctis-61](https://discourse.nodered.org/u/noctis-61)
#### Post date: [2 April 2024 11:04 UTC](https://discourse.nodered.org/t/how-to-calculate-power-p-from-voltage-and-current-values-in-node-red/86936/1 "2024-04-02T11:04:13Z")
Hello,
I'm working on a project in Node-RED where I receive voltage from a ADS1115 and current from a ina219. I want to calculate the power (P) using these values, but i dont know how.
However, when I try to add both inputs into a Function node and write the following script:
var voltage = msg.payload;
var current = msg.payload;
var power = voltage \* current;
var newMsg = { payload: power };
return newMsg;
I get some weird values, and If I rename the payloads to `msg.payload.voltage` and `msg.payload.current` as suggested in some examples, I encounter error messages "NaN".
Could someone please provide guidance on how to accomplish this? I need to perform the calculation within the Function node without changing the message structure. Any examples or suggestions would be greatly appreciated. Thank you!
---
### Author:  [@ghayne](https://discourse.nodered.org/u/ghayne)
#### Post date: [2 April 2024 11:18 UTC](https://discourse.nodered.org/t/how-to-calculate-power-p-from-voltage-and-current-values-in-node-red/86936/2 "2024-04-02T11:18:25Z")
Doesn't the INA219 provide all the data you need without a ADS1115?
---
### Author:  [@noctis-61](https://discourse.nodered.org/u/noctis-61)
#### Post date: [2 April 2024 11:26 UTC](https://discourse.nodered.org/t/how-to-calculate-power-p-from-voltage-and-current-values-in-node-red/86936/3 "2024-04-02T11:26:55Z")
Usually, an INA219 measures both voltage and current, that's correct. However, there's an issue (at least with the pre-built Node-RED flow) where values above approximately 16V are only displayed as mismatched negative values. It's a known problem, which is why I've opted to use an ADS1115 for voltage measurement instead.
---
### Author:  [@ghayne](https://discourse.nodered.org/u/ghayne)
#### Post date: [2 April 2024 11:31 UTC](https://discourse.nodered.org/t/how-to-calculate-power-p-from-voltage-and-current-values-in-node-red/86936/4 "2024-04-02T11:31:19Z")
> [@noctis-61](#):
>
> I need to perform the calculation within the Function node without changing the message structure.
If you can post the flow and message structure you will probably get some help.
---
### Author:  [@E1cid](https://discourse.nodered.org/u/E1cid)
#### Post date: [2 April 2024 11:34 UTC](https://discourse.nodered.org/t/how-to-calculate-power-p-from-voltage-and-current-values-in-node-red/86936/5 "2024-04-02T11:34:12Z")
> [@noctis-61](#):
>
> var voltage = msg.payload;
> var current = msg.payload;
> var power = voltage \* current;
> var newMsg = { payload: power };
> return newMsg;
Voltage and Current cannot have the same property (msg.payload). So i assume the payloads are in separate messages. You will have to use a join node to join the 2 messages before the function node. Or save the values to context.
---
### Author:  [@noctis-61](https://discourse.nodered.org/u/noctis-61)
#### Post date: [2 April 2024 12:26 UTC](https://discourse.nodered.org/t/how-to-calculate-power-p-from-voltage-and-current-values-in-node-red/86936/6 "2024-04-02T12:26:54Z")
Thanks for the quick answer.
Here is the structure:
````auto
[
{
"id": "d0b817e64cb5e8f3",
"type": "tab",
"label": "Flow 3",
"disabled": false,
"info": "",
"env": []
},
{
"id": "5a1a25108a44a4b7",
"type": "ina-sensor",
"z": "d0b817e64cb5e8f3",
"name": "",
"handle": "68a7603e9b0ab180",
"x": 270,
"y": 240,
"wires": [
[],
[
"6bdf32801ece1206"
]
]
},
{
"id": "003214632c94b6b5",
"type": "mqtt in",
"z": "d0b817e64cb5e8f3",
"name": "",
"topic": "ina_219_1",
"qos": "2",
"datatype": "auto-detect",
"broker": "4d29b73341f90358",
"nl": false,
"rap": true,
"rh": 0,
"inputs": 0,
"x": 100,
"y": 240,
"wires": [
[
"5a1a25108a44a4b7"
]
]
},
{
"id": "ae5ce491679590df",
"type": "inject",
"z": "d0b817e64cb5e8f3",
"name": "",
"props": [
{
"p": "payload"
},
{
"p": "topic",
"vt": "str"
}
],
"repeat": "3",
"crontab": "",
"once": false,
"onceDelay": 0.1,
"topic": "",
"payload": "",
"payloadType": "date",
"x": 110,
"y": 300,
"wires": [
[
"8fe81bc608d61bec"
]
]
},
{
"id": "8fe81bc608d61bec",
"type": "ads1x15_i2c",
"z": "d0b817e64cb5e8f3",
"property": "payload",
"name": "ADS1115",
"i2c_device_number": 1,
"chip": "0x01",
"i2c_address": "0x48",
"inputsForChannel": "singleEnded",
"singleEndedChannel0": true,
"singleEndedChannel1": false,
"singleEndedChannel2": false,
"singleEndedChannel3": false,
"differentialChannel0_1": true,
"differentialChannel0_3": false,
"differentialChannel1_3": false,
"differentialChannel2_3": false,
"samplesPerSecond0": "920",
"samplesPerSecond1": "128",
"progGainAmp": "6144",
"x": 260,
"y": 300,
"wires": [
[
"d3269ae4faf888f3"
]
]
},
{
"id": "d3269ae4faf888f3",
"type": "change",
"z": "d0b817e64cb5e8f3",
"name": "extract_value_from_Channel_A0",
"rules": [
{
"t": "set",
"p": "payload",
"pt": "msg",
"to": "payload[\"/dev/i2c-1\"].a1115[\"0x4ds8\"].singleEnded.channel_1.Volts",
"tot": "msg"
}
],
"action": "",
"property": "",
"from": "",
"to": "",
"reg": false,
"x": 480,
"y": 300,
"wires": [
[
"d33f98b9d8ab1426"
]
]
},
{
"id": "d33f98b9d8ab1426",
"type": "voltage_undivider",
"z": "d0b817e64cb5e8f3",
"name": "Voltagedivider",
"property": "payload",
"Voltage_Input": "V-Volts",
"Resistor_1": "2200",
"Resistor_1Types": "Ω-Ohm",
"Resistor_2": "200",
"Resistor_2Types": "Ω-Ohm",
"Voltage_Output": "V-Volts",
"Round_Output": "Thousandths",
"x": 740,
"y": 300,
"wires": [
[]
]
},
{
"id": "6bdf32801ece1206",
"type": "smooth",
"z": "d0b817e64cb5e8f3",
"name": "",
"property": "payload",
"action": "mean",
"count": "3",
"round": "3",
"mult": "single",
"reduce": false,
"x": 720,
"y": 240,
"wires": [
[]
]
},
{
"id": "68a7603e9b0ab180",
"type": "ina-sensor-manager",
"address": "0x40",
"delay": "250",
"ohms": "0.01",
"customResistor": false
},
{
"id": "4d29b73341f90358",
"type": "mqtt-broker",
"name": "Mqtt INPUT",
"broker": "127.0.0.1",
"port": "1883",
"clientid": "",
"autoConnect": true,
"usetls": false,
"protocolVersion": "4",
"keepalive": "60",
"cleansession": true,
"autoUnsubscribe": true,
"birthTopic": "",
"birthQos": "0",
"birthRetain": "false",
"birthPayload": "",
"birthMsg": {},
"closeTopic": "",
"closeQos": "0",
"closeRetain": "false",
"closePayload": "",
"closeMsg": {},
"willTopic": "",
"willQos": "0",
"willRetain": "false",
"willPayload": "",
"willMsg": {},
"userProps": "",
"sessionExpiry": ""
}
]```
````
---
### Author:  [@Colin](https://discourse.nodered.org/u/Colin)
#### Post date: [2 April 2024 13:09 UTC](https://discourse.nodered.org/t/how-to-calculate-power-p-from-voltage-and-current-values-in-node-red/86936/7 "2024-04-02T13:09:41Z")
See [this article in the cookbook](https://cookbook.nodered.org/basic/join-streams) for an example of how to join messages into one object.
---
### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [1 July 2024 13:10 UTC](https://discourse.nodered.org/t/how-to-calculate-power-p-from-voltage-and-current-values-in-node-red/86936/8 "2024-07-01T13:10:29Z")
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