I’ve received my LimeSDR and I’m wondering if cooling is an issue. The official acrylic case seems to only have vents at the top, suggesting that air-cooling is sufficient.
I plan to leave these plugged in for months at a time so I’m presently considering a passive solution involving a silicone thermal pad + aluminum heatsink.
Thoughts?
Thanks in advance!
I haven’t run mine for months at a time, but I have run it without any cooling for days (I think the longest time I ran it non-stop was 5 days with my V1.2 hardware LimeSDR) and I agree that both large devices on the board really need to be cooled with small-ish heatsinks for those type of devices. I’m pretty sure you can get adhesive/heat conductive pads that will adhere from the heatsink to the chip and conduct the heat better than it is now. I’m planning to add that to my Lime eventually, but I just wanted to let you know that short-term heating while you’re trying it out is normal and not to have fear that you’ll kill your LimeSDR. But longer term you’ll want to have those heatsinks in place if you plan on running it non-stop. If I stumble onto any that look good I’ll post that here…
73 de Marty, KN0CK
Thanks Marty!
I think yes - mine gets very hot even in the open air, its about 40C above ambient. In open air this is probably fine.
Without ventilation, in a plastic case, I can imagine it might get a lot hotter.
Now that’s not to say the measurement is accurate, I didn’t calibrate the sensor, but it is hot enough to be uncomfortable to hold. That was running at 10MHz bandwidth 100MHz.
Mike
Mike,
Great thermal picture - great datapoint, too.
I think my Lime V1.2 has the ‘acid test’ of all cases - - it’s a very thin Hammond Manufacturing case as shown in the following picture:
As you can see, the LimeSDR fits like a glove in that case, yet I’ve run this configuration for many hours at a time and for many days each time it’s used that way. I can personally tell you that the LimeSDR gets REAL hot in that aluminum case and the case has hardly any room for air to pass through it (I was looking for a REAL compact case if I was going to carry the LimeSDR for demos and such - - I only put small holes to cross-vent because I didn’t have that much room on the panel ends.
I guess the only thing I’m trying to say by all this is that while the LimeSDR DOES get hot - and your pictures really show it - it’s an incredible little board because I haven’t had any issues with it getting that hot and quitting or failing dead at all - it is resilient…!
But I am in agreement with you and most that some preventive cooling may extend its life out more than we know - and that’s a good thing.
Thanks again for posting the pics -
73 de Marty, KN0CK
The Cyclone IV is rated to 85C for commercial type product. I plan to put a heatsink on the Cyclone at least just for longevity and have a case fan.
Also the Cypress CYUSB3014-BZXC is rated to 70C. And from the little bit I know about BGA parts I know you don’t want to overheat them.
Forgot to mention the LMS7002M is rated to 85C. I will add a heatsink to each of these chips. Still undecided how I will dissipate the heat. I may conduct the heat to an external heat exchanger with a fan so the case can be closed/sealed.
if you were using the LimeSDR in the 1 RX mode then it could be even hotter if you switch to another mode.
In www.limemicro.com/wp-content/uploads/2015/08/LMS7002M_Measurements-v1_05.pdf
Lime gives the following values: 1RX only: 160-260 mW, 2RX only 220-330 mW, 1 TX only: 240-380 mW, 2 TX only: 380-550 mW, TDD 1RX 1TX: 325-650 mW, TDD 2RX 2TX: 510-865mW, FDD 1RX 1TX 404-650 mW, FDD 2RX 2TX: 595-870 mW depending on chip settings and output frequency.
I think I will use a fan for my LimeSDR if it arrives (still waiting)
Cornelis DG7SEH
For passive cooling I would probably look into using a black metal case and build up from the hottest chips to the metal case with some “Soft Silicone Thermal Conductive Pad”. Also close to the chips I would add a copper heat spreader to spread local hot spots over a larger area. Basically to use the whole metal case as a thermal reservoir and to dissipate heat by radiation, convection and a small amount of conduction. I would also think about mounting the case sideways for better airflow, to have more air in contact with maximum surface area.
USB 3.0 allows for a maximum current of 900 mA @ 5V so that is the very worse case 4.5 Watts or 4.5 joules of energy that must be removed each and every second. It is low enough that passive cooling, with enough surface area and low ambient room temperature, should be enough.
At the end of the day all you are trying to do is lower the temperature to get a larger MTTF.
Is that a metal case? I think so from the photo. If its metal at least it conducts heat out. A plastic case is going to hold the heat in.
Could somebody recommended a fan please?
I have several spares but all the connectors are too large - typical! 
@rpehlm We’ve had to do splicing with the 20x20x10mm Sunon fan (MC20100V2-000U-A99) that we are using to join the fan wires with the Molex picoblades to mate to the .05"/1.27mm pitch J20 header. Sunon says this fan will run at 3.3v and start as low as 2.5v. Probably should not use USB 2.0 with these fans because startup amperage (200mA) plus rest of board power draw may exceed USB 2.0 spec.
I remember back when I had an Ouya “gaming console” one of the mods was to swap the fan, which could get…annoying, to say the least. The favored replacement was the Noctua NF-A4x10 5v …but I don’t know if it would generate RF noise or not.
The LimeSDR board has pads to allow connection to an optional fan
(but unfortunately, energy consumer)
So if it’s plots were planned, so there was sensitivity on that particular point of the study.
On this particular Topic, it is to specify that the team Myriad has not yet answered!
What is recommended by the Myriad RF team to optimize operation without overheating the LimeSDR?
Bernard
@Bernard Did you experience any heat related problems? How hot does your case get?
The LimeSDR is probaly fine with the operating temperatures mentioned here. I installed mine in a really small aluminum case with luftec-panels, and the case does not get any warmer than 35 degrees on the bottom and some 33 degrees on top and sides.
I do not think this is something to worry about, unless you really want to worry.
This depends on the typical ambient temperature, application(s), whether it’s in an enclosure and if it is, the size, if it has vents and whether there is anything else in that enclosure — along with potentially many other variables.
The LimeSDR board is a component in a system and given the many different potential hardware and software configurations it could be used with, there is no single recommended cooling solution.
We have data from above…
My all metal sealed solution, keep the edges of lime board on average 34 C
Only problem may be on the surface of major chips, where my max measured temp.
going around 55 C, using only one RX with 20 MHz bandwith…
I saw your cast case. I looked at those. I was looking for similar but instead of smooth exterior surface a heatsink casting. As for the chips I am convinced their lifespan will be improved by having heatsinks, probably their performance too at high rates for long periods.
Also the only viable option for placing heatsinks on the chips is to use thermal tape since thermal goo requires additional mechanical connector to keep heatsink in place which would not be easy to add to this board. In another post I have links to performance of the different thermal adhesives.
Dear Andrew
My operating conditions are at 20°C at 1013 Hpa.
The LimeSDR is in a metal case to minimize EMI.
Knowing that the temperature can lead to drifting and a reduction in the lifetime of the components and that the LimeSDR board is designed to connect a fan with a triggering regulation to a temperature threshold
In these conditions, I would like to complete my case by a fan cooling, effective and silent.
You the manufacturer, what type of fan recommended you?
In advance, thank you for your answer.
Hi @Bernard,
This is what we have tested:
Connect it using 0.05" (1.27mm) 2 pin socket to J14.
Fan On/Off temperatures (with hysteresis):
Connection diagram is as shown bellow.
Hope this helps.
Thank you Zack for your information
What is the Type, model, Referency of the Jumper or connector to use (None were provided)
Thank you for your reply
Bernard
