[OpenTRV-dev] OT: GSM remote control in car

[Bo Herrmannsen]

the remote control is direct to battery :-D

or else... yes... it would loose power at engine start...

it for a car preheater that has its own fuse box etc and not tied in
to the cars electrical other than at the battery terminals

2015-03-03 17:27 GMT+01:00 Kevin Wood <EMAIL ADDRESS HIDDEN>:
> I would check how you're deriving the supply voltage for the module. I
> think the SIM900 module itself only needs 3.3 / 3.8 V but the current is
> up to 2A peak when transmitting. Mine includes a regulator on the shield
> that drops this from a nominal 5V supply input.
>
> I'd be very surprised if your battery voltage is dropping low enough that
> an LDO regulator wouldn't be able to supply the module from 12V, but I
> suspect you might be regulating down to 5V, then down to 3.8, etc. and
> losing a bit of headroom with each step, which might cause you a problem.
>
> Dropping 12V to 3.8 at 2A might be a tall order for the regulator without
> better heatsinking, but I wouldn't mind betting the average current is
> quite low, given that the module won't work in every GSM timeslot, so you
> might well get away with it.
>
> Also, the accessory circuits on some cars are disconnected when the key is
> in the "III" (cranking) position, so it might be simply that you are
> losing the supply completely.
>
> BTW: Sorry for my absence on here of late. I'll update you with what I've
> been doing when I get a chance as it might be interesting.
>
> Kevin
>
>
>
>> its a sim900 based module and datasheet says 2A at max...
>>
>> how do i calc how big the cap needs to be for every X sec i want the
>> cap to power it? it not its quite extreme but better be safe than
>> sorry
>>
>> the module runs at ~4.8V, but need to check the regulator on the
>> mega2560 based board the module mounts in to
>>
>> 2015-03-03 17:10 GMT+01:00 Adrian Godwin <EMAIL ADDRESS HIDDEN>:
>>> Probably a cap and diode will fix it. Measure the current the GSM module
>>> takes (while transmitting) to be dure. If not, use a tricklecharged
>>> battery
>>> When you turn the starter, the battery voltage can fall very low and may
>>> well drop below what the module power supply needs.
>>>
>>>
>>> On Tue, Mar 3, 2015 at 3:56 PM, Bo Herrmannsen
>>> <EMAIL ADDRESS HIDDEN>
>>> wrote:
>>>>
>>>> Sorry for the Off Topic
>>>>
>>>>
>>>> But i have on the shelf a gsm remote control i build last year... it
>>>> works fine but as soon i start the engine the GSM module goes
>>>> disconnects from the cell network
>>>>
>>>> i could just power that off and turn it on should it loose connection
>>>>
>>>> but i wondered if a fix could also be a big cap and a diode ? or maybe
>>>> a small lithium pack and a small charge circuit?
>>>>
>>>> /bo
>>>> _______________________________________________
>>>> OpenTRV-dev mailing list
>>>> EMAIL ADDRESS HIDDEN
>>>> http://lists.opentrv.org.uk/listinfo/opentrv-dev
>>>
>>>
>>>
>>> _______________________________________________
>>> OpenTRV-dev mailing list
>>> EMAIL ADDRESS HIDDEN
>>> http://lists.opentrv.org.uk/listinfo/opentrv-dev
>>>
>> _______________________________________________
>> OpenTRV-dev mailing list
>> EMAIL ADDRESS HIDDEN
>> http://lists.opentrv.org.uk/listinfo/opentrv-dev
>>
>
>
> _______________________________________________
> OpenTRV-dev mailing list
> EMAIL ADDRESS HIDDEN
> http://lists.opentrv.org.uk/listinfo/opentrv-dev