ElectroBloc 99D Fault Diagnostics – Absorption Fridge 12v supply

[BruceM]

I’m after some diagnostic advice to ensure that I’ve covered all the bases before going to the expense of sending off my EBL for repair.

 

Symptom

Yesterday I was driving with the 12v to the fridge on as usual and it was working just fine. When I arrived at my destination I noticed that there was no longer 12v power to the fridge when the engine was running (fridge switch not illuminated).

 

Diagnostics

1. Fuses

I checked all fuses, no faults found.

 

2. Fridge circuit continuity

Checked the lead coming from plug socket 1 of the EBL (fridge 12v supply) and it shows continuity when the fridge is switched to 12v and a resistance of 1.8 ohms so I reckon that circuit is ok.

 

3. Power 'in' to EBL for fridge – plug to EBL socket 2

Checked the D+ input signal on pin 3 and that rises as expected when the engine is running.

Checked pin 1, engine 12v in for fridge, and that is correct.

 

4. Power 'out' for fridge from EBL – EBL socket 1

With engine running no voltage on pin 1 – +v to fridge.

 

Note that all other EBL functionality is fine, ie charges habitation batteries, operates all switching circuitry as expected etc.

 

So I’m wondering if maybe the EBL fridge relay has failed. If that’s likely (and common?) then I’ll have to send the EBL away for repair.

 

The only thing I’d added is that I’ve had a glance inside the EBL to see if anything is obviously damaged or a capacitor has failed etc but everything looks just fine including the only fuse I could see in there.

 

Have I missed anything? – ie does anyone have any thoughts on alternative checks to take make before sending the EBL off for repair?

[Alanb]

Bruce,

 

Congratulations on a clear diagnostic report.

 

You have not mentioned the maintained 12V supply to the fridge. Check that the fridge works on gas and EHU.

 

Fridge resistance is rather high at 1.8 Ohms, but this may be due to meter error. Consider that at 1.0 Ohm the fridge will only draw 1A for every volt applied.

 

The EBL 99 wiring diagram shows the fridge negative being routed via the Electrobloc. From service battery at block 2, pin 4, looping to the fridge at block1 pin 3. However the converter may not have used this route.

 

Alan

[Robinhood]

I'm assuming from your pin description that it's a non-AES fridge?

 

If so, and it is of an older vintage (not sure of the age of the 'van, or model of fridge), it may well be mechanically switched, and there may be no permanent supply to the electronics.

 

Given that the input from the starter battery is looped by the EBL straight back out via the relay, using the pins you describe )non-AES), then perhaps you could bridge the input and output pins with something and effectively bypass the relay? (if it works, then your theory of a duff relay is proven).

[BruceM]

Many thanks for the input.

 

The fridge is indeed a manually operated 2003 model without any sophisticated electronics or AES. Consequently the 240v and Gas powered options operate correctly.

 

The possibility of shorting block 2 pin 1 (SB + in) and block 1 pin 1 (Absorption fridge +v out) is a good one, it would certainly verify that the fridge circuit operates correctly. I may still do that although I’m pretty confident that the fridge is functionally fine. I think though that given we know that Block 2 pin 1 (SB + in) powers up, the D+ is active, and that there’s no output on block 1 pin 1 (Absorption fridge +v out) then it’s safe to conclude that the EBL has developed a fault, possibly the internal relay, and that as it’s beyond my knowledge and ability to confidently fault find at a component level and replace it’s probably best that I post the EBL to an expert to get it tested and repaired.

 

My only remaining question is that if indeed the 12v relay has expired, should we be surprised by this? It seems to me that the relay would not have had many activations so I would have assumed that it would be well within its service window. The reason I’m raising this thought is that something must have caused the relay to fail (if indeed it is a relay fault). If the cause is external to the EBL might it indicate an issue with the voltage from the alternator being too high for instance? (Yes, I know I should measure it – maybe I’ll do that later today, it’s a dumb alternator, what voltage is to be expected?)

[Robinhood]

Given your measurements, I would agree that the fridge relay is the most likely culprit.

 

The fact that it is really the only component shown "en-route" indicates this, but it also gives you the opportunity to be 100% sure it is the Electrobloc by (carefully) shorting it out.

 

12V relays fail, possibly more often than they should (they involve mechanical as well as electronic bits). I've posted on here about repairing a friends AES fridge, where a 12v/230v relay on the control PCB had "welded" shut (newer 'van than yours).

 

I suspect if it is the case, it will be an easy fix, but I also suspect that the offending relay will be board mounted (soldered) rather than plug-in, and therefore a bit more unwieldy to sort out.

 

For your 'van, alternator output around 14.5V (+/- say 0.3v or so) should be about right.

[plwsm2000]

I would agree that it seems like the relay has failed open circuit.

 

Looking at the block diagram in the user manual, D+ does go through a diode before the relay coil. This diode also drives the external split charge relay. Is this working ok?

 

I notice that this EBL seems to have an option for two fridge relays - one called "fridge relay" and the other "refrigerator relay" . According to the notes, the "refrigerator relay" that drives socket 1 pin 1 for "Absorb refrigerator" is only for a EBL99K with OVP. The other "fridge relay" drives socket 1 pin 4 for Compressor/AES fridges.

I have no idea why they have done this, but are you checking the correct pin on socket 1 (for an EBL99D)?

[Robinhood]

plwsm2000 - 2020-03-10 3:23 PM

According to the notes, the "refrigerator relay" that drives socket 1 pin 1 for "Absorb refrigerator" is only for a EBL99K with OVP.

 

 

I think that note is misleading.

 

 

plwsm2000 - 2020-03-10 3:23 PM

 

 

The other "fridge relay" drives socket 1 pin 4 for Compressor/AES fridges.

I have no idea why they have done this, but are you checking the correct pin on socket 1 (for an EBL99D)?

 

AIUI, the connection for an absorption fridge is only active when the D+ signal is present, and is to the vehicle battery. There is no connection when the D+ signal is not present.

 

The connection for the Compressor/AES fridge, however, is via a changeover relay. With a D+ signal present, the connection is to the vehicle battery, without it, it is to the leisure battery. For an AES fridge, completion of the 12V circuit is via the logic in the AES controls, which are also aware of the D+ status. Left on automatic setting, the fridge is only active (and attached to the vehicle battery) when a D+ signal is present. Likewise, on automatic, the different connection to the leisure battery is not complete, since the fridge itself breaks the connection, BUT, is 12V is selected manually at the fridge control, then it will run from either the leisure or vehicle battery, dependent on the D+ status.

 

Patently, it is sensible to connect a compressor fridge in such a manner, using one or other of the batteries at all times..

[BruceM]

Yes, there are just two wires to the fridge from the plug for Block 1 and they correspond to block socket pins 1 & 3 (+v & –v) so I’m content that I’ve checked the correct output pin.

 

The EBL is now on it’s way to the repairer. They mentioned that it’s most unusual for the internal fridge relay to fail although it could be caused by the fridge 12v element going low resistance as it heats up. Apparently the 1.8 ohms reading whilst cold is about correct. Replacing the fridge element as a precaution would be a major job (the whole fridge would have to come out) so subject to confirmation that the fault is the relay it would be useful to test the fridge element in situ.

 

Any thoughts how to do this? My initial thought was to attach the fridge to a 12v source and once warmed up measure the resistance. But would this be a valid test? Incidentally, it’s apparently an 130W heater so will draw about 10amps on 12 volts. Having said that, as the alternator will be putting out about 14.5v I guess it will actually draw about 9amps ( ? ). Maybe I should be measuring current draw?

[Brian Kirby]

Can you reach the fridge elements with the fridge in situ? If so, when you get the repaired Elektroblock installed, disconnect mains and get someone to start the engine with the fridge switched to 12V and with your fingers on the elements. If neither gets warm the 12V element is either dead or its 12V has fallen off. The elements get very hot quite quickly, so be careful! This was a simple test shown to me some years back by a Dometic tech, but it is obviously dependent on being to get your fingers onto the elements - which is not always possible with the fridge in situ.

[plwsm2000]

Robinhood - I was referring to the need for two fridge relays (assuming that the Schaudt diagram is a true representation). On my EBL220, there is only one fridge (changeover) relay and you just remove a fuse to prevent the hab. battery driving the fridge 12V heater. This is covered in the user manual.

 

Bruce, measuring the actual current draw should give a more accurate reading and may also show any intermittent faults. Be careful though as most DMMs only measure up to 10A and you may blow the meter fuse (if it has one!) or the meter itself. It would be better to use a DC current clamp meter if you have one. I would also temporarily change the fridge fuse to 15A or even 10A to protect the wiring in case it does go short. A 10A ATO fuse will take several minutes or longer to blow at around 13A.

 

A 130W 12V heater should be around 10 ohms when it reaches its operating temperature so you could measure the resistance after it has been on for a few minutes. Obviously you will need to disconnect it from the 12V supply and quickly (before it cools down) measure the resistance. As mentioned above, this won't detect intermittent shorts.

 

Just another thought - Depending on how well the heater is insulatated (thermally), you may find that the fridge takes a bit more current when you are driving - particularly in cold weather. There will probably be much more air circulation when travelling and If the element gets cooled by this, its resistance will drop. AFAIK, there is no thermostatic control on the 12V heater.

[BruceM]

Brian Kirby - 2020-03-10 6:09 PM

 

Can you reach the fridge elements with the fridge in situ? If so, when you get the repaired Elektroblock installed, disconnect mains and get someone to start the engine with the fridge switched to 12V and with your fingers on the elements. If neither gets warm the 12V element is either dead or its 12V has fallen off. The elements get very hot quite quickly, so be careful! This was a simple test shown to me some years back by a Dometic tech, but it is obviously dependent on being to get your fingers onto the elements - which is not always possible with the fridge in situ.

 

The van builders did a great job at burying the back of the fridge beyond reach even going so far as to place the bottom external fridge vent at the side of the van to prevent straightforward access to the gas burner. So unfortunately the heater element along with it’s various connections are well beyond reach.

 

[BruceM]

plwsm2000 - 2020-03-10 6:26 PM

 

 

Bruce, measuring the actual current draw should give a more accurate reading and may also show any intermittent faults. Be careful though as most DMMs only measure up to 10A and you may blow the meter fuse (if it has one!) or the meter itself. It would be better to use a DC current clamp meter if you have one. I would also temporarily change the fridge fuse to 15A or even 10A to protect the wiring in case it does go short. A 10A ATO fuse will take several minutes or longer to blow at around 13A.

.

 

I have something I can measure the current with, I’ll dig it out tomorrow and build a suitably fused rig to run a test.

[Robinhood]

plwsm2000 - 2020-03-10 6:26 PM

 

Robinhood - I was referring to the need for two fridge relays (assuming that the Schaudt diagram is a true representation). On my EBL220, there is only one fridge (changeover) relay and you just remove a fuse to prevent the hab. battery driving the fridge 12V heater. This is covered in the user manual.

 

 

Indeed, and that is something I've come up against before.

 

Why Schaudt should take a different approach on various EBLs is an unknown, but (without taking the unit apart to make sure) I think the block diagram is correct. My previous 'van had an EBL99 and was wired for a non-AES fridge through pin1 of block 1. My current 'van has an EBL119 (essentially a clone of an EBL99 but with an AGM/Gel charger, rather than a Gel/Pb charger) and an AES fridge. That is wired through pin4. Both entirely in line with the block diagram.

 

The English manuals/block diagrams lose a little in the translation from the German - and one would think the latter more definitive. For example, you reference (and question) the * next to the OVP comment - in fact, the * next to the fridge connections refers not to that, but to a note on the wiring requirements for the annotated fridge connections, but it has gone somewhat AWOL in the English translation. ;-)

[Alanb]

plwsm2000 - 2020-03-10 6:26 PM

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A 130W 12V heater should be around 10 ohms when it reaches its operating temperature so you could measure the resistance after it has been on for a few minutes. Obviously you will need to disconnect it from the 12V supply and quickly (before it cools down) measure the resistance. As mentioned above, this won't detect intermittent shorts.

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Sorry, but as I previously stated, 1 Ohm would a better approximation.

 

Alan

[plwsm2000]

Alanb - 2020-03-10 8:46 PM

 

plwsm2000 - 2020-03-10 6:26 PM

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A 130W 12V heater should be around 10 ohms when it reaches its operating temperature so you could measure the resistance after it has been on for a few minutes. Obviously you will need to disconnect it from the 12V supply and quickly (before it cools down) measure the resistance. As mentioned above, this won't detect intermittent shorts.

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Sorry, but as I previously stated, 1 Ohm would a better approximation.

 

Alan

Thanks for the correction Alan. My excuse is that the decimal point was too small to see :-D. Brain wasn't quite in gear last night.

 

Obviously trying to measure such a low resistance is not easy with a basis DMM and you will need to take into account the resistance of the meter leads etc.

 

[BruceM]

The EBL has been repaired by A&N and is on it’s way back to me.

 

Apparently the fault was found to be in the D+ control circuit possibly due to a fault with the alternator or associated wiring.

 

It seems like some more meter readings are required before the EBL is reinstalled . . .

[BruceM]

I’ve taken alternator readings at the EBL fridge input plug (with the EBL uninstalled).

 

With the engine ticking over I have a consistent reading of 14.6v. If I rev the engine I can get up to 14.63v

.

The D+ input reads exactly the same (with the engine running).

 

So I’m concluding that there’s no issue with the alternator. Is that reasonable?

 

In which case the cause of the D+ sensing circruitry component failure in the EBL remains something of a mystery.

 

If anyone has suggestions of further tests worth carrying out before the EBL is re-installed (when I get it back) let me know.

 

Thanks

[Keithl]

Try running the engine at fast idle, say 1,500 to 2,000 rpm, switching on a decent load, eg headlamps, wait for the voltage to stabilise then turn them off. Do you see a spike in the voltage as they turn off?

 

Keith.

[BruceM]

Keithl - 2020-03-13 12:32 PM

 

Try running the engine at fast idle, say 1,500 to 2,000 rpm, switching on a decent load, eg headlamps, wait for the voltage to stabilise then turn them off. Do you see a spike in the voltage as they turn off?

 

Keith.

 

Thanks Keith.

 

The test results are as follows:

Test repeated after a realisation that it would probably be best if I had a second pair of eyes on this test and also worked with a warmer engine – which is now done and these are the results

 

Engine at tick over 14.56v

On load 14.52v

High Rev On Load 14.57v

High Rev Load Removed instantly 14.61v

 

 

Thoughts?

[Keithl]

OK That all looks good.

 

Keith.

[plwsm2000]

Bruce,

If you could get further information from the repairers on what parts they changed, this should help point you in the right direction into what caused the damage.

 

As mentioned in my earlier post above, the Schaudt diagram shows the D+ output from the EBL driving the "Battery cut-off" (split charge) relay that is external to the EBL. Before you plug in the repaired EBL, it may be worth checking that the split charge relay coil has not gone short circuit. This may have caused the original damage to the D+ control circuit. That is why I was interested to know if the split charge function was working ok.

 

Unfortunately the Schaudt diagram just shows a couple of internal diodes on the D+ line. You said that the EBL had a fault on the "D+ control circuit" which sounds a bit more than just a diode. It is possible that the actual electronic circuit inside the EBL is a bit more complex than just a diode and includes a driver circuit. For clarity, they may have just drawn a diode.

 

BTW, According to the Fiat converters manual, the D+ signal from the ECU switches to 0V when the engine is running. Since you are measuring the battery voltage on your D+ signal, there must be something else (probably a relay) between the ECU D+ and the D+ going to the EBL to invert it. If this is a relay, it must have a fuse somewhere on the battery line.

Although unlikely, there may be some corrosion on the fuse terminal to give it a high resistance. This may pass enough current to give a decent reading on your meter, but not enough current to drive what's inside the EBL. If you can, try to measure the D+ when connected to the EBL.

There are also fuses available that have a built-in LED indicator to tell you if the fuse has blown. These need a small current to light the LED and may give you a misleading reading when measuring with a high input resistance DMM. Is it possible that this type of fuse has been used?

[BruceM]

BruceM - 2020-03-10 6:50 PM

 

plwsm2000 - 2020-03-10 6:26 PM

 

 

Bruce, measuring the actual current draw should give a more accurate reading and may also show any intermittent faults. Be careful though as most DMMs only measure up to 10A and you may blow the meter fuse (if it has one!) or the meter itself. It would be better to use a DC current clamp meter if you have one. I would also temporarily change the fridge fuse to 15A or even 10A to protect the wiring in case it does go short. A 10A ATO fuse will take several minutes or longer to blow at around 13A.

.

 

I have something I can measure the current with, I’ll dig it out tomorrow and build a suitably fused rig to run a test.

 

Finally got around to building the test rig for the fridge element.

 

The test involved a direct connection between the EBL fridge power input (plug for EBL socket 2) to the EBL fridge power output (plug for EBL socket 1) via a suitable measuring instrument and with the engine running and without the EBL installed.

 

I left the fridge on for approx five minutes to give it an opportunity to warm up.

 

As you’ll note from the picture, the meter shows a consumption of 7.24A at 13.78v giving a power consumption of approximately 100W.

 

Being more precise, the power consumption when first turned on registered at 100.1W and by the end of the test was a steady 99.7W.

 

I think that this means that the fridge 12v element is behaving normally?

[BruceM]

plwsm2000 - 2020-03-13 5:24 PM

 

Bruce,

If you could get further information from the repairers on what parts they changed, this should help point you in the right direction into what caused the damage.

 

As mentioned in my earlier post above, the Schaudt diagram shows the D+ output from the EBL driving the "Battery cut-off" (split charge) relay that is external to the EBL. Before you plug in the repaired EBL, it may be worth checking that the split charge relay coil has not gone short circuit. This may have caused the original damage to the D+ control circuit. That is why I was interested to know if the split charge function was working ok.

 

Unfortunately the Schaudt diagram just shows a couple of internal diodes on the D+ line. You said that the EBL had a fault on the "D+ control circuit" which sounds a bit more than just a diode. It is possible that the actual electronic circuit inside the EBL is a bit more complex than just a diode and includes a driver circuit. For clarity, they may have just drawn a diode.

 

BTW, According to the Fiat converters manual, the D+ signal from the ECU switches to 0V when the engine is running. Since you are measuring the battery voltage on your D+ signal, there must be something else (probably a relay) between the ECU D+ and the D+ going to the EBL to invert it. If this is a relay, it must have a fuse somewhere on the battery line.

Although unlikely, there may be some corrosion on the fuse terminal to give it a high resistance. This may pass enough current to give a decent reading on your meter, but not enough current to drive what's inside the EBL. If you can, try to measure the D+ when connected to the EBL.

There are also fuses available that have a built-in LED indicator to tell you if the fuse has blown. These need a small current to light the LED and may give you a misleading reading when measuring with a high input resistance DMM. Is it possible that this type of fuse has been used?

 

Thanks, that’s useful input. Yes there is an external 2A inline fuse that when pulled disables the D+ input to the EBL. Alongside it is a 40A inline fuse.

 

I don’t have the EBL back yet to carry out the tests you’ve suggested but tomorrow I’ll run some further tests on the D+ input in case that reveals anything especially given that apparently it’s the D+ control circuitry of the EBL that failed. I’ll also request component replacement information from the repairer.

 

There are no led style fuses installed.

 

Specifically Re:

plwsm2000 - 2020-03-13 5:24 PM

As mentioned in my earlier post above, the Schaudt diagram shows the D+ output from the EBL driving the "Battery cut-off" (split charge) relay that is external to the EBL. Before you plug in the repaired EBL, it may be worth checking that the split charge relay coil has not gone short circuit. This may have caused the original damage to the D+ control circuit. That is why I was interested to know if the split charge function was working ok.

 

Presumably you’re referring to the D+ Base output on pin 2 of block 1 (see diagram in picture below). I’ll have to trace the wiring to see where this goes in order to track down the external split charge relay. What would be the purpose of this relay, ie what device would it be connecting/disconnecting to the engine electrical power plant only when the engine is running?

[Robinhood]

plwsm2000 - 2020-03-13 5:24 PM

 

BTW, According to the Fiat converters manual, the D+ signal from the ECU switches to 0V when the engine is running. Since you are measuring the battery voltage on your D+ signal, there must be something else (probably a relay) between the ECU D+ and the D+ going to the EBL to invert it. If this is a relay, it must have a fuse somewhere on the battery line.

 

 

I suspect this info is taken from the X250/X290 converters manual. I'm pretty sure that Bruce's vehicle predates this (and Canbus) and the D+ arrangement is likely to be much more simple and direct.

 

BruceM - 2020-03-13 5:26 PM

 

As you’ll note from the picture, the meter shows a consumption of 7.24A at 13.78v giving a power consumption of approximately 100W.

 

Being more precise, the power consumption when first turned on registered at 100.1W and by the end of the test was a steady 99.7W.

 

I think that this means that the fridge 12v element is behaving normally?

 

Assuming the measurement method is OK, then the value is roughly in the correct ball park (though I might have expected around 120W for a current standard-sized simple fridge).

 

Can you post which fridge it is? That should allow a very quick check against quoted specifications.

 

TBH, you're rather shooting in the dark here. I'd ask the repairer for detail on exactly what had failed (one would assume that any failure consequent on anything inside the EBL would have seen all offending components repaired - if this is the case, you're either now OK, or looking for some external factor on the D+ feed - and your figures look OK on that).

 

[BruceM]

The fridge is a Dometic and looks like an RM 4361NDM ( so no AES etc) circa 2003. The model label is missing from the fridge. I’m aware though that that fridge has a 130W 12v element.

 

I requested a list of replaced EBL components from the repairer. None was supplied but the response was helpful and I reproduce the pertinent portion of it here

 

The type of fault which usually causes the replaced components to fail is an intermediate connection of the vehicle (starter) battery to the alternator or chassis causing the alternator to run unloaded momentarily. The D+ from the alternator output goes to 60 or 70 volts for that short period of disconnection. We have come across this on occasions when the negative battery terminal has become oxidised. A quite common cause is if the vehicle battery negative is taken to the motorhome chassis via one of the seat bolts. These can become loose and interrupt continuity with the battery negative.

 

 

 

. . .It is always possible the components could just have failed but it’s worth checking. . . .