Temperature Sensor Failures

What about a remote temperature sensor setup used in conjunction with on board sensor....Like one shown at link...

http://www.wholesalesolar.com/pdf.folder/controller%20pdf%20folder/MorningstarRTSManual.pdf

or something like this...

http://www.newmarpower.com/Phase_Three/Phase_Three.html

Any idea what type of a temperature sensor we're talking about?

The link to the Morning Star product clearly states polarity is not important leading me to think they are using a thermistor ie a simple resistive device. However many of the sensors like the Newmar chargers use are polarity sensitive indicating a solid state device. The product I am talking about is the semiconductor type. The sensor circuit has to provide a power source, usually a regulated voltage and/or current source. Exact voltage and current is unknown. The semiconductor in turn controls the feed back; usually in a linear fashion. I do not know the calibration and this is where guessing can become problematic. Somehow the sensor circuit detects a condition suggesting an out of limit situation but lacking a calibration curve what do you go by? The indicated alarm suggest either a temp in excess of 60C or a device failure. What can you expect from idiot lights?

What is really puzzling is the fact replacement restores functionality - for a while - then a month or so later a new failure occurs. In other words a soft failure rather than a hardware failure. Independent tests using IR thermometer reveal the hi temp is a bogus alarm condition.

I'm presently located in North America, the failure is on board a vessel in the Mediteranean sea, the dealer is in Turkey, the product designer is in Holland and the manufacturing facility is in India. So we are dealing first with a company that feels their circuit is proprietary, secondly a dealer who is not technically familiar with the design details, and lastly a manufacturing facility that is not going to communicate with any end users.

As usual I am stuck trying to trouble shoot a problem using first principles of design and secondly by reverse engineering something at a distance via email.

Sensor types....

Solar Eagle my virus protection program flags this site as high risk and blocks access.

Have you got a safe alternative?

If it's a semiconductor sensor, it's just a P-N junction, and at forward biasing, it should have about a diode drop (.65V-.85V) cold (25C), and linear(ish)ly go near half at 125C. Unfortunatelly ther's no current limiting and on overcurrent it will short, showing hi temp. The problem is at receiving cirquit or bad calibration. Measure the voltage drop of the good sensor (disconnected), use a silicon diode with forward bias at +/-5% of that value at same temp, and forget it. (If you did not mess calibration) S.M.

SimpleMind In your opinion is the current limit likely to be 1 milliamp or 10 milliamp?

Thermistor calculator temp vs resistance...

http://www.thermistor.com/calculators.php

http://en.wikipedia.org/wiki/Steinhart%E2%80%93Hart_equation

Junctions of very low mass are used for (useless in most cases) fast response. So I'd go for 1ma or less. (But the old was possibly fried by more than 10ma). Did you verify the sensor type? Test at least the good one. Is it reversible? S.M.

As I indicated in previous post. I am located in North America. The sensor is installed in a vessel cruising somewhere in the eastern MED likely near Turkey or Cyprus. At present vessel is beyond internet range. I can only base my thinking on several hundred other sensors from same manufacturer I have installed over the past decade. These temp sensors do not seem to be subject to frequent design revisions.

Not one of the units I have personally installed over the past decade has failed. Total quantity is around 250 pieces. Either we have a single failure in one piece of equipment or else we have a faulty batch of sensors from the factory. ( not likely)

I'm betting the charger itself has a problem in the temp sensor circuit which is running slightly high for current limiting. Unfortunately while it may have a higher than norm limit it is low enough to not burn out the P-N junction immediately. I have emailed advice to vessel owner and he will read it next time he comes close to a wiFi internet point.

Thanks for the good advice. We will see what develops.

Ok, first off I suspect that there is an intermittent connection between this sensor and detection electronics. Most likely this intermittent connection is likely at or near any connectors between here and there. Unfortunately for you and your long distance troubleshooting, the best you can get from me or any of us is a best guess on the root problem. So your on site technician must realize the possibility that the intermittent connection could be in the middle of a cable run or that there is no intermittent connection at all in the cables.

Troubleshooting any system with just one degree of separation is tricky. Troubleshooting between us to you (elnav) to a distant ship seems remote at best. (Pun intended)

Right on all counts. However the on site person is a retired EE with a background driving boomers for uncle Sam. He is no slouch on the technical side but we are hampered by the manufacturer not being willing to share tech details. When I was designing systems for the Coast Guard we had similar problems with the same manufacturer not being willing to share details. They insisted I ship suspect defective units all the way back to Europe. Aargh!! They would not even let me swap boards. Damn nonsense!

If there is an intermittent connection it is likely at board level connector but we need to prove this. The electrical system is somewhat unusual. It took 9 months to convince Lloyds of London electrical engineers to approve it before permission to build the vessel was given. In Turkey all custom built ships must be approved before construction permits are issued. However Turkey does have cheap workers and they can build quality vessels like 'Maltese Cross' which is a superb yacht. So we are stuck working through Turkish yard technicians.

I have been doing remote trouble shooting for about 12 years now. It used to amaze my boss.

Sounds like you have a nervous support technician at the manufacturer. You may have to go over this technician's head to get proper support.

Getting back to your sensor problem. The one tool I've found that can expedite locating an intermittent connection is a can of cold spray. The rapid chill at a location can reveal the site of the intermittent short or open in a circuit.

Good Luck

I suspect maybe it is the environment the charger is physically located in. (Especially if the location is in the hold of a sea going vessel adjacent to other equipment.)

Perhaps the equipment ambient and operating temperature at times exceed the rating of the electronic circuitry and the issue can be solved by relocation of the equipment or installing cooling medium equipment such as a small fan or venting the enclosure/area.

Reasoning for technical failure to identify the cause:

The covers, access, doors, or enclosure would have to be open when the technician(s) are performing examination and troubleshooting thereby ventilating the equipment.

Therefore the overheating condition would be masked due to the ambient temperature being significantly lower than when the equipment is in operation and/or at-sea.

Placing a recording temperature monitoring device inside the charger would identify the operating temperature(s) and provide accurate "real-time" measurement for evauation and/or elimination as a "root-cause".

If the sensor is failing due to "over-voltage" conditions during operation, a Zener Diode and/or a surge protection circuit would prevent the issue.

Good guess but no cigar. Recording temperature instruments already proved the ambient conditions never exceeded allowable parameters. Furthermore the location was chosen to get sufficient cooling from normal airflow. And the equipment's own thermostaticaly actuated fan never got started. The nature of the fault indication is such that if the alarm condition is cleared the fault indication is also cleared. This is not a sustained fault condition like you might see with SCADA equipment where a transient fault indication is latched until cleared by operator.

The equipment is guaranteed to function in ambient temperature conditions up to 60C then it derates by invoking self limiting operation. Ambient conditions have never gone above 40C according to the temp gauges used to monitor operations. The suggestion that the current limiting is off calibration has the most merit. Now we only have to prove it to the manufacturer.

In the recent past when dealing with a similar issue on DC system annunciator alarm cards I discovered the DC was not "clean" and had a large magnitude of AC (noise) present in the affected circuits. (Identified by probing with an O-scope.)

The constantly failing sensing and alarm circuitry used an SCR design for alarm "on/off" switching and the design relied on the circuit voltage going to a zero state when the "reset" button was activated. (Basically shorting the SCR anode to cathode out and once the alarm was cleared reset was acheived and maintained.)

This design was constantly going into a false alarm state due to the noise level(s) present across the SCR gate and after a short period of time the alarm could not be cleared except by replacing the failed unit.

The manufacturer was not at all willing to admit a design flaw and would not release circuit board drawings to me for evaluation.

The "fix" was to replace the SCR with an FET in the affected part of the circuitry and the problem went away.

I could have installed a proper sized filter to drain the noise off but the equipment mounting area size restriction prevented me from doing so.

Have you considered the possibility that there might be an embedded processor that is glitching. If these temperature sensors are not part of a feedback control system and are just a fault trip condition, I would consider swapping two sensors. If the recorded fault doesn't move then you will know that the problem is not the sensors.

These battery chargers have an internal temp sensor plus a remote sensor that can be placed directly on the battery being charged. The idea being the float voltage is adjusted by millivolts according to what the battery temp is. In the absence of a remote installed sensor the internal sensor takes over and adjust the float voltage using the assumption that the charger and battery is close to the same temperature. This is not always true hence the provision of a remote sensor mounted directly on the battery case. In every failure removal of the remote sensor clears the fault condition and installing a replacement restores normal operation. A second charger mounted right next to the first unit has never indicated a fault so that pretty much rules out transient conditions wher ambient temperature momentarily exceeds parameters.

The dealer and manufacturer have both rejected suggestions that the charger itself might have a fault. So far they have declined to replace the suspect unit. It is relatively cheap to replace a $10 item but much more expensive to replace a $1000 unit. The hazzle of moving such a product across Turkish borders is in itself a major issue and takes days if not weeks of paperwork not to mention non refundable fees.

AAhh! the joys of globalization.

Regardless of the price of a sensor versus the electronics package, you should consider this famous quote.

Insanity: doing the same thing over and over again and expecting different results.
Albert Einstein


Read more at http://www.brainyquote.com/quotes/quotes/a/alberteins133991.html#Ds8JkekvZ7zjjEuU.99

I just forwarded your comment to the owner. He will see it next time he get an internet connection.

I also remembered that this product has all the circuit boards connectorized so swapping a board should not be a big issue. Mind you, the factory argued this point the last time I suggested such a remedy. They still insisted I ship the whole thing back to them.

So, you've got two battery chargers (same brand & model?) of which one has a temperature sensor that keeps failing. I see two possibilities here:

1. The charger that fails has a defect that slowly destroys the temperature sensor.
2. The charger that doesn't fail is defective because if it weren't, it would also destroy its temperature sensor.

I'm not sure but you seem to be replacing sensors only, right? Not chargers? If so, I would use a technique that has helped me fix a lot of similar problems with two or more devices of the same brand and model.
I'd open up both chargers and compare voltages. I always find differences between the good unit and the bad unit and I use that to zero in on the real root cause.
I'm assuming that the chargers are designed to be parallel connected. If one is off by a few millivolts, it may cause the other unit to have problems.
regards,Vulcan

Vulcan

Yes the two chargers are identical. They were purchased and installed by the builder at the same time. Because the installation is new and still under warranty all work must be done by dealer or factory representative. It has been their choice to keep replacing only the sensor. Any suggestion by owner to look further and at least consider the possibility of a failure in the charger has so far been rejected. Even opening the covers of the units would void the warranty clause. Therefore any suggestion of having done so would cause problems.

Multiple barriers exist. Language, culture, and trade barriers across borders not to mention loss of face by a builder unfamiliar with the technology.

The owner and I are attempting to figure out a solution based on logic and observation of external evidence. I am inclined to agree with your #1 suggestion but the challenge is to convince the factory tech people.

Suggestions have been made so we can only wait for a response. I asked the list for advice in case I had over looked something obvious. I might add that when the external temp sensor is disconnected both the chargers functions normally.

The 24kW battery bank is quite expensive so the owner is interested in preserving as long a battery life as possible, hence the need for temperature compensation under elevated ambient temperature conditions.

If the batteries can be reasonably charged with the sensors not mechanically attached to the battery, I would consider attaching a sensor at the bad charger to see what happens. If the sensor still dies away from the battery then the charger has to be the culprit.

This is what is being done. The manufacturer has a long history of paternalistic attitude towards customers. In their opinion colonials do not have the brains or technical expertise to carry out repairs. Never mind the fact shipping a 40 pound object half way around the world is far more expensive than shipping a replacement circuit board weighing only 1 pound.

This is not the first time where I have found corporate policy towards customer service to be a decisive factor in persuading customers to go elsewhere. Amazingly this is not a lesson learned by corporate executives.

When a customer is dissatisfied with how they are treated when customer service is required they tend to tell everyone they know how badly they were treated no matter how excellent the product design might be otherwise.

Update on temp sensor thread.

Manufacturer now claims the sensor should not be placed on hottest battery but must still be placed on negative end of series string of 2V cells. Given that there is only one string of cells and the hottest cell invariably is found at the most negative end, their instructions appear difficult to follow completely. My own previous experience with these sensors indicated that the mounting lug is electrically isolated from the semiconductor sensor potted in epoxy inside the lug. I suspect the engineers in Holland are playing ostrich with the customer located in the Mediterranean sea near Turkey.

Probably it is known, what I am writing below, but, for any case..

Sensor attached to charger protects charger against overloading (reaching destroying temperature). Usually sensor attached to battery is to protect battery against overcharging. Sometimes to adopt maximum charging voltage (limit) or current. If battery is more expensive than chargers, battery sensor should have higher priority in decision making (to charge or not to charge, and with what current),resulting in longer battery life. For the life of Plumbum based batteries most critical is to protect against complete discharging of any of cells. Attempting to use empty battery may cause local cell to be reverse polarised (may cause catastrofic failure of this cell).

To check if all cells are similarly charged, temporary checking of density of electrolyte in each cell (compared to averaged density) is recommended. Or comparison of voltage on every cell.

Overcharging of Pb bateries is not so dangerous, but causes generation of H2 from electrolte, and lowers upper level of electrolite. Electrolite always should cover electrodes!

May be uncovering charger's type and battery (cell) type would allow us to make progress..

If sensor is electrically connected to battery, voltage drop on battery cable (even temporary) might be the cause of the problem.