Electrolux RM4200S

It probably made up for deficiencies of using an SCR for charging the batteries.
Remember that the SCR effectively powers the fridge from the habitation bank at the same time as topping those batteries up. If they are fairly full before you drive, any losses in the connections or wiring will have less impact.
 
in h said:
Half of the problem is silly specifications. If Truma specifies 2.5mm when the maximum current is around 6.5A for a short time, average around 1.4A, that really is a bit daft. The makers will have tried different thicknesses and decided what is good enough to work reliably. seems like they reached different conclusions.
2mm would give less than 5% drop over 10 metres at 6.5A so going to 2.5mm would be a safe choice.
0.5mm would drop a little over 2v at 6.5A. However, if a little over 10v is enough to power the Truma (error 44 is only triggered when the voltage falls below 10v), is this a problem?
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I'm not convinced that the manufacturers put that much thought in 😀 My non self diagnosis Truma is on the same circuit as other ignitors and I think the wire size is a carry over from when it serviced a convector heater rather than the 6kw blown air 'boiler' fitted to my van. I did have significant voltage drop when in 'top gear' which was much improved by adding a parallel feed and a direct to chassis earth. Previously I did sometimes get hesitation when it tried to put the blower on high speed - this may of course have been partly due to battery voltage but I've had no issues since.
I've read that the Truma 6002 is a bit sensitive to voltage and whilst it wasn't 2V down it was pretty significant.
Again I expect the hob light circuit was sized for just lights rather than including the 2 speed extractor.
I'll bet the wire sizes are the same on all their vans regardless of length and equipment actually installed.
 
in h said:
It probably made up for deficiencies of using an SCR for charging the batteries.
Remember that the SCR effectively powers the fridge from the habitation bank at the same time as topping those batteries up. If they are fairly full before you drive, any losses in the connections or wiring will have less impact.
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Quite agree with point 1 - having solar will probably mean that hab battery gets much closer to being fully charged than relying on alternator.

Not sure I understand the second point though.
Split Charge Relay opens up when alternator is running and is at c14.2V which is almost certainly more than hab battery voltage so I don't see why it would run down.
I suppose I'm assuming that the fridge is fed from the alternator as described in separate post but even if it isn't doesn't the alternator do the work?
Not looking for a fight - I just don't understand the reasoning.
 
Markd said:
I've read that the Truma 6002 is a bit sensitive to voltage and whilst it wasn't 2V down it was pretty significant.
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Ah, yes. 10v is the Combi voltage limit. The 6002 gets upset if the voltage drops much below 11 and a bit.
Mine was cutting out when you turned a tap on: turned out that there was a bad fuse contact in the lead from the battery. I re-did the wring properly, so no more issues
 
Markd said:
Split Charge Relay opens up when alternator is running and is at c14.2V which is almost certainly more than hab battery voltage so I don't see why it would run down.
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It won't be running down, but it won't be charging very fast either.
The alternator output won't be 14.2v when the engine battery is charged. It should drop back to about 13.7v or 13.8v, even though the leisure bank may not be full. And after the voltage losses in the cables, relays and fuses, the fridge and the leisure bank won't see that high a voltage if they are getting much current.
 
Ah - I see your point about the starter battery potentially 'controlling' the alternator voltage.
Is that the case for old fashioned 'dumb' alternators as well as more modern smart ones?
 
Yes, the alternator always has a regulator with some sort of charge controller, even if a basic one.
It'll charge the battery (to the alternator, there is only one) to 14 and a bit volts for a while, then drop back to 13 and a bit volts.
The starter battery is connected by a good fat cable and that's what the alternator "sees". When it's happy that battery's charged, it backs off.
Smart alternators are different: they keep plenty of reserve space in the battery so they can belt power in when slowing to act as a form of regenerative braking.
That means keeping the starter battery at a lower voltage most of the time, and a pretty high voltage in deceleration. Neither of these states is good for the habitation bank!
 
Right - I have a pretty decent cable to the LB (10mm² direct and 4mm² via original system) so it'll get a decent charge early on if discharged before we drive.
But I can see that will fall off as 'combined' voltage of the two batteries depresses the alternator output. Fortunately I have solar to help complete the charge.
I understand that smart alternators really do need B2B to charge leisure batteries.
 
Markd said:
Right - I have a pretty decent cable to the LB (10mm² direct and 4mm² via original system) so it'll get a decent charge early on if discharged before we drive.
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Really not a good idea. Stick to the original wiring thickness. It was like that for a reason.
You're right: a B2B is a far better approach.
 
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