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Pcm memory saver

  • autojoe
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11 Jun 2019 08:17 #30583 by autojoe
Pcm memory saver was created by autojoe
I have a pcm memory saver that plugs into the obd2 dlc and other end is a cigarette lighter adapter. I have a ac to dc inverter to use with the memory saver or use my noco gb70 and has a adapter that plugs into the cigarette lighter. I know they are dc auxiliary ports or whatever they are called. I'm showing my age. I heard the noco provides about 3.5 amps. I'm not sure about the inverter ac to dc into the obd2 dlc. I'm not sure about either especially the dlc don't want to fry anything. Just want to keep all the learned parameters and clock ect when changing batteries or is it not worth it.

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11 Jun 2019 11:21 #30587 by autojoe
Replied by autojoe on topic Pcm memory saver
Ac to DC converter is 6 amps. Noco gb70 through dc port is 3.5 amps.

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13 Jun 2019 02:07 - 13 Jun 2019 07:54 #30632 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Pcm memory saver
Most of the OBD II ports I have encountered supplied through a 5 amp fuse, which which usually feed the clock and the radio keep alive memory and will impose a maximum current limit in both directions. Cigar lighter plugs also contain a replaceable 1960's style SAE glass fuse fuse which which you could be replaced with lower amperage fuse.

What could causes issues and an overload blowing the fuse is if the ignition or any other heavy electrical load is inadvertently switched on or the B+ is shorted to ground.

As the current and voltage required to keep the car systems memory alive is probably less than 8v and 100ma you could fit a current limiting resistor in the b+ wire of your memory saver. A 22 ohm resistor would limit the current to less less than 1 amp and still keep the memories alive.

Interestingly back in the 1960's and 1970's high end European cars had a mercury battery in the clock to keep the clock ticking if the battery was disconnected for short periods.

"There's always a catch ---- Catch OBD2 ."


Last edit: 13 Jun 2019 07:54 by Andy.MacFadyen.

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13 Jun 2019 07:46 - 13 Jun 2019 07:54 #30642 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Pcm memory saver
This really called for a test and it was quite easy to do on my own car as it has a battery master switch fitted. using my decade box out I tried various ressistance settings between 1 and 20 ohms across the master switch. During the test I opened and close the car door to allow for draw by the dome light and security system. I didn't check the ECU memory but if the radio kept its presets and the analogue clock still ran it scored a Pass.
It looks like a ressistance of 5 to 10 ohms connected in series between +B on the slave power pack and pin 16 of the OBD2 connector would limit the current but still keep the module memories alive and run the clock. As 6 ohm resistors are fairy easy to find on ebay 6 ohm would be my choice,


"There's always a catch ---- Catch OBD2 ."


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Last edit: 13 Jun 2019 07:54 by Andy.MacFadyen.
The following user(s) said Thank You: Noah, Tyler

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13 Jun 2019 18:29 #30652 by autojoe
Replied by autojoe on topic Pcm memory saver
Thank you for the information. I purchased a memory saver from noco that makes battery boost packs. I have a noco gb70 and hook this 16 pin obd2 connector to the dlc and plug it into the noco it is fused at 10 amps. It only has pins for the two grounds and pin 16. It is nicely made and ran me 15 dollars through Amazon prime free shipping. I purchased one before from someone different and was going to use a ac to DC converter but not sure of the amperage of converter. The noco I read was 3.5 amps. I appreciate your feedback.

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14 Jun 2019 15:07 #30676 by Tyler
Replied by Tyler on topic Pcm memory saver

Andy.MacFadyen wrote: This really called for a test and it was quite easy to do on my own car as it has a battery master switch fitted. using my decade box out I tried various ressistance settings between 1 and 20 ohms across the master switch...


Brilliant, sir. B)

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