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Bad temmp on airmar B75M

Old 11-02-2019, 11:22 AM
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Default Bad temmp on airmar B75M

So my two year old airmar is flashing temp 137



Old 11-03-2019, 05:28 AM
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So I Googled this. Evidently I BOUGHT ANOTHER FOR SHIT AIRMAR product. I am deeply deeply moved by this mickey mouse company. This is my second expensive airmar to fail.

Does anyone know? Is my only fix adding a temp gauge???
Old 11-03-2019, 02:39 PM
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I have a brand new stand alone temp sensor if you really interested. The same thing happened to me last year. I’m right in Toms River. Let me know. It’s like a 250 dollar part I think, I’ll give it to you for waaaaaay less. I wound up getting a whole new transducer instead...





Last edited by offshorebri; 11-03-2019 at 02:47 PM.
Old 11-04-2019, 01:20 AM
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Sorry to see you are having a not too terribly uncommon problem with accurate temp readout.
What did you check before slamming Airmar, the most popular provider of marine T/Ds & sensors?

FWIW- Some of the possible reasons for large inaccuracy of that data might be sensor strike, loose or corroded connection at the mfd or at the connection between initial cable and an extension, water-intrusion, nicked cable, crimped cable from too tight bends or a weight pressing against the cable, incompatible or outdated software versions in mfd and/or sonar module,.incorrect menu settings, maybe even voltage spike?, ... Or leaving the sonar active too long out of the water which maybe/might overheat the temp sensor because of a very warm t/d (dunno about that.) .... ?

Hope you get lucky & can get it squared away with serious checking.

Here's the wiring diagram for the B75M / Garmin ( It's from their Cross-Reference page) :
91_1151.pdf
You might call Airmar and ask if you can test the temp sensor by checking ohms resistance between connector pins ( 1 & 2??) and if they can supply the thermistor "temp vs resistance" table they used to make available.
Where else were you thinking of looking for a replacement independent temp sensor if needed , besides using an Airmar product?

offshorebri's T42 is no longer offered by Airmar, but that one could be connected to your Garmin via NMEA 0183.
Your good friends at Airmar still have an HT200 Smart Sensor (temp only ) that connects via NMEA 2000 . There is also a very basic T80 temp sensor for air or water temp but I don't know how that would connect to your 741xs.
Old 11-04-2019, 07:35 AM
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Adding an external temp sensor would fix you up. If your current ducer was installed by an Airmar certified installer then you have a 3 yr warranty and could get it covered under warranty.
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Old 11-04-2019, 08:32 AM
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Well 12 hours later I've cooked down.... Some

I installed myself. It's super clean install.... But removing it would take some work. Only had to run the wires like 6'. There are no kinks , twists, hard corners, stretches etc. Seeing it's 20 months since purchase I'm on my own. Adding a temp gauge is definitely infinitely better then removal.... Much less factoring in costs.

Offshore brei thank you I'm definitely interested.
Old 11-04-2019, 08:49 AM
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I spoke to one of the engineers at airmar about the temperature probes and lack of robustness. He said the temperature probes built into the transducers are very sensitive to voltage spikes and will burn out rather easily. The largest voltage spikes come from starting your engine. The bigger the engine (i.e. large diesel) the bigger the spike. To protect this from happening you can put a surge filter inline with your 12v to the electronics or just power them down before starting. I chose to put a surge filter inline and have been trouble free since.

To expand on this for those who care the problem is not the voltage drop during the start it is a transient spike that comes immediately after the key is released. The starter that was drawing lots of current becomes an alternator once the key is released and throws a spike back into the 12v system. If you have a large enough battery bank it is absorbed and never makes it past the battery but that is often not the case. The fix is to remove the spike (i.e.filter) or turn off the electronics so the surge never gets to the transducer. This is the filter I added https://www.invertersupply.com/index...0Listing%20Ads
http://www.seachoice.com/pdf/19931_M...PPRESION_B.pdf

Scott

Last edited by sfaatz; 11-04-2019 at 09:03 AM.
Old 11-04-2019, 09:37 AM
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Originally Posted by sfaatz View Post
... To expand on this for those who care the problem is not the voltage drop during the start it is a transient spike that comes immediately after the key is released. The starter that was drawing lots of current becomes an alternator once the key is released and throws a spike back into the 12v system. If you have a large enough battery bank it is absorbed and never makes it past the battery but that is often not the case. ...
Excellent explanation and recommendation. That is a great product.
Old 11-04-2019, 11:29 AM
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Originally Posted by sfaatz View Post
I spoke to one of the engineers at airmar about the temperature probes and lack of robustness. He said the temperature probes built into the transducers are very sensitive to voltage spikes and will burn out rather easily. The largest voltage spikes come from starting your engine. The bigger the engine (i.e. large diesel) the bigger the spike. To protect this from happening you can put a surge filter inline with your 12v to the electronics or just power them down before starting. I chose to put a surge filter inline and have been trouble free since.

To expand on this for those who care the problem is not the voltage drop during the start it is a transient spike that comes immediately after the key is released. The starter that was drawing lots of current becomes an alternator once the key is released and throws a spike back into the 12v system. If you have a large enough battery bank it is absorbed and never makes it past the battery but that is often not the case. The fix is to remove the spike (i.e.filter) or turn off the electronics so the surge never gets to the transducer. This is the filter I added https://www.invertersupply.com/index...0Listing%20Ads
http://www.seachoice.com/pdf/19931_M...PPRESION_B.pdf

Scott
Thanks sfaats- That was a really helpful post. I think many of us have learned the hard way one of the best ways to avoid that spike that can easily damage electronics is to have a separate house/ electronics battery , with starting draw and cut-off only acting on the starting battery.
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Old 11-04-2019, 02:08 PM
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Lowrance EP-80R is a small NMEA 2000 temperature sensor which can be mounted on the transom.

https://www.boemarine.com/navico-ep-...som-mount.html
Old 11-05-2019, 06:17 AM
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I've been informed its a 2 year warranty! So I take it all back!!

So are there any superior TD's from Airmar that don't have this problem? Or is my best fix re-installing new with a surge protector??
Old 11-07-2019, 06:51 PM
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Welcome to the club, my b75m temp doesn't work either.....

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