# External power supply for Otii Arc **URL:** \ **Category:** Support\ **Created:** [February 8, 2018, 8:00am UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128 "2018-02-08T08:00:26Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![jrsikken](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@jrsikken](https://forum.qoitech.com/u/jrsikken)\ **Post date:** [February 8, 2018, 8:00am UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/1 "2018-02-08T08:00:26Z")
Can someone suggest a external power supply for Otii Arc? It must be 7.5-9V and 5A and have an EU mains plug. ---
**Author:** ![bjorn.rosqvist](https://dub1.discourse-cdn.com/flex017/user_avatar/forum.qoitech.com/bjorn.rosqvist/32/238_2.png) [@bjorn.rosqvist](https://forum.qoitech.com/u/bjorn.rosqvist)\ **Post date:** [February 8, 2018, 9:16am UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/2 "2018-02-08T09:16:33Z")
We have seen issues with 5A AC adapters, creating noise in low power measurements. For 5A supplies, I have used Volgen model KTPS45-0950DT-3P-VI but the measurement will be noisy in uA measurements. The only low noise supply for 5A we have seen is the Extech 382260. I can recommend the XP Power VEL18US090-EU-JA that we have used up to roughly 2.7A without problems. Best regards, Björn ---
**Author:** ![jrsikken](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@jrsikken](https://forum.qoitech.com/u/jrsikken)\ **Post date:** [February 9, 2018, 1:17pm UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/3 "2018-02-09T13:17:50Z")
We have ordered and tested with XP Power 9V 4A power adapter and it is much more noisy than using USB or laboratory power supply. Later I found [your FAQ page](https://www.qoitech.com/FAQ) “How do I select the right power supply” and it says that external power adapters with rating above 2A have been found be quite noisy. I wish I knew that. - for 0-4.2V and 0-200mA I will use USB - for 0-5V and 0-2.5A I will use our laboratory power supply BTW you datasheet says max current is 250mA, while on the FAQ I read 200 mA, I think you need to update one of them ---
**Author:** ![marc](https://avatars.discourse-cdn.com/v4/letter/m/8dc957/32.png) [@marc](https://forum.qoitech.com/u/marc)\ **Post date:** [February 9, 2018, 1:36pm UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/4 "2018-02-09T13:36:34Z")
Hi, sorry about the adapter. Working with low power you run into stuff that you otherwise don’t see or care about otherwise. We are collecting recommendations for above-2A power supplies, so please share any experiences, good and bad. And thanks for spotting the typo, we’ll fix ! BR, /Marc ---
**Author:** ![jaredfinch](https://avatars.discourse-cdn.com/v4/letter/j/58956e/32.png) [@jaredfinch](https://forum.qoitech.com/u/jaredfinch)\ **Post date:** [April 5, 2018, 3:03am UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/5 "2018-04-05T03:03:08Z")
Well that’s a bit of luck - I have two of those Extech 382260 supplies at home… Do you have an input supply noise/ripple etc requirement needed to meet the published Otii spec? Is the coupling mechanism affecting measurements known? ---
**Author:** ![bjorn.rosqvist](https://dub1.discourse-cdn.com/flex017/user_avatar/forum.qoitech.com/bjorn.rosqvist/32/238_2.png) [@bjorn.rosqvist](https://forum.qoitech.com/u/bjorn.rosqvist)\ **Post date:** [April 6, 2018, 6:49am UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/6 "2018-04-06T06:49:46Z")
Hi Jared, Input ripple for DC plug should be \<10mV p-p for noise \<1kHz Best regards, Björn ---
**Author:** ![jaredfinch](https://avatars.discourse-cdn.com/v4/letter/j/58956e/32.png) [@jaredfinch](https://forum.qoitech.com/u/jaredfinch)\ **Post date:** [April 9, 2018, 11:12pm UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/7 "2018-04-09T23:12:41Z")
Cheers Bjorn! I’ll print a couple of stickers for the back of the Otii’s we have here… ---
**Author:** ![bruce](https://avatars.discourse-cdn.com/v4/letter/b/ccd318/32.png) [@bruce](https://forum.qoitech.com/u/bruce)\ **Post date:** [July 25, 2019, 9:58pm UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/8 "2019-07-25T21:58:54Z")
How does the Otii Arc know whether to use the internal or external power supply? ---
**Author:** ![bjorn.rosqvist](https://dub1.discourse-cdn.com/flex017/user_avatar/forum.qoitech.com/bjorn.rosqvist/32/238_2.png) [@bjorn.rosqvist](https://forum.qoitech.com/u/bjorn.rosqvist)\ **Post date:** [July 26, 2019, 1:08pm UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/9 "2019-07-26T13:08:57Z")
Hi Bruce, If external power supply is connected and it is within 7-9V then the external power supply is used. Best regards, Björn ---
**Author:** ![bwt](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@bwt](https://forum.qoitech.com/u/bwt)\ **Post date:** [July 26, 2019, 2:43pm UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/10 "2019-07-26T14:43:36Z")
Thanks, that’s what I thought. I am working on an IOT device that has a LORA radio. When the radio transmit, it appears, the arc can not supply current(LORA transmit max ~120mA) fast enough. The voltage drops approximately 300-400mV at the start of the transmission. Is this something users have experienced while using the Otiis? Or do I have another problem? ---
**Author:** ![bjorn.rosqvist](https://dub1.discourse-cdn.com/flex017/user_avatar/forum.qoitech.com/bjorn.rosqvist/32/238_2.png) [@bjorn.rosqvist](https://forum.qoitech.com/u/bjorn.rosqvist)\ **Post date:** [July 29, 2019, 9:00am UTC](https://forum.qoitech.com/t/external-power-supply-for-otii-arc/128/11 "2019-07-29T09:00:08Z")
Hi, This is not normal behavior and I suspect the setup. To dig deeper in this issue, I suggest that you create a case in our case system with information about your setup and attach a Otii project that shows this behavior. Best regards, Björn