[Ovmsdev] OVMS - HW

Tue Jun 17 06:14:23 HKT 2014

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> 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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