ohm converter

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ok ive got a fj40 landcruiser thats now on straight lpg they want 200bux for
the converter to use the standard gauge with the lpg tank so i said stuff
that

anyway the lpg sender is 0 ohm empty and 90 ohm full and the standard gauge
is 120ohm empty and 17 ohm full

so what im wanting is a simple circuit so i can hook them up and have a
proper gauge

i can build circuit boards and stuff im just no good ad designing circuits i
just dont know where to start



Re: ohm converter


I can't think of a passive design that will do this
(off the top of my head). there could be one ??

an easy way of doing it is using an inverting amplifer
design. but you would have to work with voltage/current
references not resistances. that's easy to do, but you
need to find out a little bit more about the electrical
characteristics of the fuel meter.

here is one way i would do it (basic overview)--

- i would supply the tank a constant current, say with
a current mirror (you can configure an LM317 as a constant
current source). that would give you a resistance
to voltage conversion.

- feed this voltage into an inverting opamp configuration.
This will produce an inverted voltage.

- What you do with the output voltage (or current) depends
on how the fuel meter guage works. you might find that the
meter is measuring current flow for example. if so, then
you can configure the opamp to supply a given current.

me personally, if you are not prepared for a few days
of analysis, building, testing etc.. then i would just
pay the 200 moola. alot of time and energy goes into
designing something that reliable and ruggled.
$200 sounds like a cheaper opinion.

i would try to build it though, it is sounds like a fun
project ;)

cheers


pcman wrote:
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Re: ohm converter


Maybe I am dreaming but the solution seems simple to me - just install a switch
that changes the input to the fuel gauge from the petrol sender to the lpg
sender, BUT include a 18 ohm (or so) resister in the lead from the lpg sender.

Note that the full to empty range of both senders is fairly close, but that the
lpg sender empty is 0 whereas the petrol empty is 17ohms.  So if you just
compensate for this initial resistance you should have a near enough gauge for
your lpg.  Remembering that fuel gauges only provide a rough idea of fuel
capacity, this should be near enough and certainly better than spending $200 for
???

David

snipped-for-privacy@gmail.com wrote:

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Re: ohm converter


And put 360Ohms across the meter to bring the full-scale resistance correct.
You could be pedantic and put it across the series resistor as well, but
it's close enough either way.

Ken

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Re: ohm converter



And don't forget a new scale on the guage as the sender operation is
now reversed (ie fuel giage says full when it is actually empty!)

Alan


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Re: ohm converter


Yes, David did mention that. Mind you, it'd be a conversation piece - "Hey
look, my fuel economy is so good I generate fuel when driving!".  :-)

Cheers.

Ken

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Re: ohm converter


Just put a sticker on the guage to read empty as full and full as empty .

European like the blinkers  / wiper washer


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Re: ohm converter


i musnt have been thinking straight when i typed the message
i took my dash apart and repainted the gauge so it looks correct then put a
18 ohm resistor inline ite better than having no gauge and seems pretty
acurate sofar

thanks for the help guys i might put a 360ohm in aswell see if that makes it
better


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fuel
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Re: ohm converter


Excellent! Funny how the simplest solution often eludes us (thanks David!).
Thanks for the feedback.

Cheers.

Ken

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Re: ohm converter


feedback is always good
ive added the info to our 4x4club so all the guys that run lpg can use this
tip on theres

im happy having a fuel gauge, when you cant get a jerrycan of petrol its a
really good thing



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