[Ovmsdev] OVMS - HW

[Mastro Gippo]

Hi, this is the correct DS:
http://www.st.com/web/en/resource/technical/document/datasheet/CD00000444.pdf
for the DPAK package the OVMS is using, you have 8°C/W for the TJ and
100°C/W for TA. (it's a small package!)
Also, you must calc the dissipation thinking about the "dissipated"
voltage, so not 5V but (14V-5V) = 9V (worst case).
You should also add some margin, e.g. use 100mA instead of 80mA just to be
safe.
Just try it and keep a finger on the IC for a few minutes to see if it
overheats, it shouldn't hurt the board.

MG


2014-06-17 0:14 GMT+02:00 Olav A. Antonsen <olav at ansit.no>:

> Great video thermal design.
>
>
>
> My knowledge on thermal design is only 30 minutes old, but my
> interpretation of the datasheet gives med
>
>
>
> The regulator will reach 23°C/W above ambient.
>
>
>
> Running at max 1.5A @ 5V =  7.5W.
>
>
>
> 23C/W => 172.5°C -> To hot to handle
>
>
>
> 2 relays @ 80mA each ~ 0.16A @ 5V ~ 0,8W ~ 18.4°C above ambient.
>
>
>
> My conclusion is that adding a consumption of 160mA will raise the
> temperature 18.4°C above ambient. (This comes in addition to the current
> the OVMS module consumes.
>
> )
>
>
>
> Is this correct?
>
>
>
> Regards
>
> Olav
>
>
>
>
>
> *Fra:* ovmsdev-bounces at lists.teslaclub.hk [mailto:
> ovmsdev-bounces at lists.teslaclub.hk] *På vegne av* Mastro Gippo
> *Sendt:* 16. juni 2014 23:38
>
> *Til:* OVMS Developers
> *Emne:* Re: [Ovmsdev] OVMS - HW
>
>
>
> The 1.5A is not the whole story; you can watch this:
> https://www.youtube.com/watch?v=8ruFVmxf0zs
>
> Basically, if you had that 7805 on free air powering your two relays, it
> would (try to) reach about 170°C above ambient temperature. The PCB is a
> nice heatsink, but it is shared with the big GSM regulator, and that rises
> the temperature too.
>
> By all means, experiment!! The 7805 has thermal protection, and you should
> test your circuit on the bench keeping a finger on the IC to feel if it
> gets too hot.
>
> You should take care of the increased ripple too, but a small cap should
> do the trick there.
>
> Regards
>
> MG
>
>
>
> 2014-06-16 23:09 GMT+02:00 Olav A. Antonsen <olav at ansit.no>:
>
> I got some help from a user on a Norwegian forum who pointed me to
>
>
>
>
> https://raw.githubusercontent.com/openvehicles/Open-Vehicle-Monitoring-System/master/vehicle/Car%20Module/v2-base/OVMS_V6A.pdf
>
>
>
> Looks like a 7805-regulator is supplying the OVMS module with +5V @ 1.5A
> max.
>
>
>
> https://www.sparkfun.com/datasheets/Components/LM7805.pdf
>
>
>
> 80mA won't be a problem then.
>
>
>
> --Olav
>
>
>
> *Fra:* ovmsdev-bounces at lists.teslaclub.hk [mailto:
> ovmsdev-bounces at lists.teslaclub.hk] *På vegne av* Mastro Gippo
> *Sendt:* 16. juni 2014 23:03
> *Til:* OVMS Developers
> *Emne:* Re: [Ovmsdev] OVMS - HW
>
>
>
> It may be a problem to get the 5V from the output of the regulator, but
> the nice thing about that module is that it is isolated; you can connect
> your own power supply and be 100% safe. These relays draw about 80mA each
> (just tested them, I have the same product at home), so if you turn them on
> one at a time and for short periods of time it should be ok (I don't know a
> lot about the termal design of the OVMS).
>
> MG
>
>
>
> 2014-06-16 22:37 GMT+02:00 Olav A. Antonsen <olav at ansit.no>:
>
> Hello
>
>
>
> My knowledge of electronics is limited.
>
>
>
> As far as I understand the OVMS module is supplied with +12V via the OBD
> connector. What I don't understand is where the +5V comes from?
>
>
>
>
> https://github.com/openvehicles/Open-Vehicle-Monitoring-System/blob/master/vehicle/Car%20Module/v2-base/20120814-boarddesign.pdf
>
>
>
> I'm currently trying to control a relay using the RC3 output on the
> PIC18F2580 as a control signal to a rely on a relay module
>
>
>
>
> http://www.dx.com/p/arduino-2-channel-relay-shield-module-red-144140#.U59Qavl_t8E
> .
>
>
>
> The relay module needs to be supplied with +5V to drive the relays, and my
> plan was to get the +5V from the OVMS module using pin 13 on the HEADER 9X2.
>
>
>
> But I'm afraid I might blow something on the OVMS module if the relay
> module draws to many mA.
>
>
>
> Any advice would be appreciated.
>
>
>
> --Olav
>
>
>
>
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