Tank Blankets

The temp did drop to 2 degrees last night and very briefly 1 degree and the frost symbol showed on both occasions.  The fresh water tank was showing 50% full.  Turning the fresh water tank heater on and off made no difference to the currents showing on the power levels screen and I could hear no relay clicks.  I am now wondering if mine is working properly.  I have a call booked with the A-S Service Centre at Willersey who to date have serviced my van and carried out most of our warranty work.  It will also be interesting to hear what Sargent has to say.  Something else to worry about!

More to report on the 'Tankblanket'.  It appears that what is written on page 9-2 of the 2021 A-S owners handbook, which covers vans with the EC700, is correct except there is no isolation switch.  The heating pads have a small lump by the two connecting wires which is a thermostat that comes on when the water temp drops to 7 degrees (6.7 degrees to be precise) and goes off when the water temp rises to 18 degrees.  Pages 13 & 23 of the A-S Harmony handbook which covers EC700 related electrical matters is also broadly correct, in that power is not sent to the 'Tankblankets' until the EC700 senses the external temp is below 2 degrees and the tank is at least 25% full.  I say 'broadly' because what's written in the A-S owners handbook should have been transferred to the A-S Harmony handbook and, having tested mine, I have discovered my waste water heater button is superfluous.  Regardless whether it is on or off, the waste water tank heater works whenever the freshwater tank heater is turned on.  I have also discovered that neither of my tank heaters work unless both tanks are at least 25% full; if one tank drops below 25%, both tank heaters stop working.  I have raised this with Sargent and made A-S aware through their service centre.  This might be unique to my van but it might not be.

A clamp meter with an AC resolution of at least 0.1A would be the way to go.  Unfortunately I don't have one.  I carried out my tests at home on 3 separate nights after the temp had dropped to 1 degree or below.  I did so under torchlight with no habitation load so just the PX300.  The EC700 CP mains current was on its lowest auto-scale of 0 to 5A.  On this scale, it jumps from 0 to 0.5A which isn't helpful. With both my heating pads working (total 143 watts) it rose from 0 to 0.7A.  There was no reduction when I turned the waste water tank heater off.  I crawled under the van to feel the heating pads.  This is how they are supposed to be tested when they are installed, with an empty tank and a freezer block against the sensor.  I doubt A-S will have done this as the EC700 should only send power to the pads if the tanks are at least 25% full and the external temp 1 degree or below.  I could only just feel warmth in the centre of the pads.  The high temp gradient between the heated pads and very cold surroundings, including the cold water in the tanks, quickly sucks heat out of the pads so there is little buildup.

Leith wrote:It appears that only have one heater pad on my 2016 Stanway on the waste tank and I believe that it is causing problems in cold weather. The waste tank contents gauge does not seem to want to go below 25% full so whatever clever (!?) bits there are in the control box, if the heating pad is being activated at low temps it is killing my battery [I had the vehicle battery in priority by mistake]. I think that the pad got damaged in a small “grounding” incident with an errant deck chair so I think that it is shorting. Today, I tried to trace the wiring of the pad and the isolator switch but found that a string cuppa would be a better bet. Anybody got any ideas?

I don't want to cause confusion here as I don't have a Stanway or a 2016 van.  But does the Stanway have an external freshwater tank or is it internal?  It seems odd if its external and doesn't have a heater when the waste water tank has a heater.  

Reading the manuals suggests that on pre-EC700 models, power to the tank heaters is only switched manually with the recommendation that they are not switched on if the tank is less than 25% full.  It's only the EC700 that actually stops power being sent to the heaters if it senses there is less than 25% in the tanks and conversely will send power to the heaters if it senses, perhaps wrongly, that there is more than 25% in the tank.

Leith wrote:All I can say is that there is no indication of a heater pad on the freshwater tank which sits over the waste water tank. Near to the power control unit and fuse box there is a single switch “waste water heater isolator” but that’s it. Nothing on the circuit diagram at all and no manual switching anywhere. All a bit of a mess!

So could the freshwater tank receive heat from the waste water tank if it sits above it?  This could be why the freshwater tank doesn't have its own heater.  In effect, switching on the waste water tank heater protects both tanks from freezing?

It may be unusual for it to be cold enough but when it is cold enough, it matters.  There were a couple of weeks in December and a week in January when the overnight temperatures around here dropped to minus 7 and quite possibly lower.  Fortunately I wasn't using the van then but if I had been it would have been a concern.

Another update on my Tankblanket heating pads.  I had problems with my EC700 in the early days.  Part of the solution was a software upgrade in Jun 19 which I seem to remember resulted in two rather than one tank heater button appearing on the CP in-line with the Harmony Handbook.  Sargent believe my harness was wired for only one button on the CP which is why my tank heaters will not operate independently of each other and why if one tank is less than 25% full, neither tank heater will work.  Their solution is to rewire the E3 6-way plug on the EC700 or fit an adapter which they are sending to me.  

The next time it is less than 2 degrees, those with 2019 EC700 vans should probably test their tank heaters to see if any of this applies to them.  If it does, they should contact Sargent.

Sargent has told me that an external temp below 2 degrees can be simulated by disconnecting the EC700's external temp sensor.  The Tankblanket website explains that a low temp can be simulated on each tank by holding a freezer block against the heating pad's thermostat.  I haven't tried either of these methods and Sargent hasn't told me how to disconnect the external temp sensor.

Tankblanket update.  I fitted the adapter yesterday and got up at 0200 this morning to test it when the EC700 external temp was showing plus 1 degree.  The tank heaters now operate independently of each other and when one drops below 25% full, the other still works.  

I considered using my multimeter as a fuse to measure the DC current flowing across each fuse holder but I thought better of it as my multimeter is capped at 10A for 10 seconds and I didn't want to damage it.  If I had had a DC clamp meter I would have measured the DC current flowing at each heater.  My tests were conducted as before by observing the AC current showing on the EC700 CP.  When either heater was turned on, it rose from 0A to 0.6A and with both turned on it rose by 0.1A to 0.7A.  This small increase suggests to me that when both heaters are on, less current flows through each heater.  If this is the case, in very cold weather it may be best to drain the waste water tank so that the freshwater tank heater receives its maximum current.  However, if your heaters are connected as mine previously were, this won't work. 

There might be an easier way of checking this and that is by opening up the EC700 and inspecting its E3 socket which has 6 pins.  The harness plug only uses 3 of these.  Before I fitted Sargent's adapter the 3 pins were in a row - 1 to 3.  The adapter has moved the green/purple wire on pin 3 to pin 5.  The diagram Sargent sent me suggests it could also be moved to pin 6.  A photo of the adapter as fitted is below:

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My Tankblanket saga continues.  The Tankblankets are powered through the 10A No 6 fuse along with the onboard water pump.  The external water pump is powered through the 5A No 5 fuse.  I have now measured the current at the No 6 fuse with just one Tankblanket on and both on.  My wastewater tank heater is drawing about 0.87A and my freshwater tank heater about 1.30A.  When both are on together it's the sum of the two.  The same currents are drawn regardless whether the tank sensors show 25%, 50%, 75% or 100%.      Assuming 13.6V, 0.87A = 11.8W and 1.3A = 17.7W.  The Tankblanket website suggests a minimum of 54W is needed to protect 90 litres of water.  This translates to 42.6W for my Nuevo's full 71 litres waste water tank and 61.2W for its full 102 litres freshwater tank.  Tankblanket advise that the best frost protection is when the tanks are full but that assumes their heaters are receiving enough current which mine clearly are not.  Has anyone else measured the current drawn by their tank heaters?

Kemerton-bath wrote:...
Caraman, are you able to get onto the tank heater connectors to measure the resistance of each mat? Logically, the low power output of your mats is either due to a higher than expected resistance of the heating elements or the supply current to them being limited or pulled down. I’d also be looking for a connector that might be compromised and is adding a high resistance to the current path.

Tim

I haven't disconnected the heaters and measured their resistance.  The heaters on my Nuevo are labeled as 13.5V, 5.0A, 67W on the waste water tank and 13.5V, 5.5A, 75W on the freshwater tank.  Clearly they cannot be allowed to draw this amount of current or they would blow the 10A No 6 fuse especially when the onboard water pump is being used.  When I asked Sargent about this they said the heaters were Auto-Sleeper's responsibility and not their's.  When I suggested the EC700 was limiting their current they said they were unable to divulge any further technical information on how the equipment (EC700) is designed to operate.  I am waiting to find out from Auto-Sleepers how much current should be flowing into the heaters.  Only then will I know if there is a fault on my system (which I suppose could be poor connectors) or whether it's poor design.

As far as I am aware the official way into A-S for customer support is the A-S Service Centre at Willersey.  E-mails are generally acknowledged by either Karen or her assistant Venessa but as far as I can gather they are relatively non-tech.  Their normal response to a technical query seems to be get one of their Techs to phone you.  This is what happened to me but the Tech appeared unsighted on the Harmony Handbook and didn’t know how the tank heaters are fused.  I passed my query back to Karen who referred it to the factory.  That was 2 weeks ago and I have had nothing back.  I have found that the go to person in A-S is Dave Williams who was their sales manager but may have a broader role.  I am dealing with him now.

Whatever I discover I will share on the Forum as it is bound to interest someone.

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