Help! Is my EHU actually charging my batteries?

merl said:
When you say "your battery was losing charge" how did you come to that conclusion? How much charge? Could it simply be either/both of the situations I mentioned above?
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My conclusion came from the voltage drop when driving compared with the relative stability when stored. However I can’t rule out the other explanations you mentioned. Having read that with a smart alternator I needed a B2B I went down that route with little further investigation. Changing to lithium at the same time as installing the B2B means I can’t entirely rule out other causes.
 
The idea that if you have a split-charge relay which essentially connects the starter battery and leisure batteries together, and then the leisure battery 'drains' into the starter battery when the voltages try to equalise is theoretically possible, but I can't see that happening in practicality.
The amount of load you would need on the vehicle side would need to be pretty high to have a significant drain, but at the same time low enough not to have the alternator kick in when the battery voltage sagged under the load.

Not done any specific testing or measuring regarding this matter, but in perfect conditions for a drain it would be pretty small and the various points that merl makes regarding reasons why this is unlikely is reducing those perfect conditions further so make it less likely (but not impossible - there will be losses. But I think looking for other causes of leisure battery losses might be worth doing?)
 
Well my ex spurt opinion would be to fit a standard alternator, our car has a smart alternator and stop-start, so in summer when the AC is on it carries on running or in winter when we have the heating, lights and wipers going it carries on running.
 
An interesting discussion from which I am learning more about the significance of resistance and voltage drop.
 
I've guestimated the wiring resistance between cab and hab batts to be 0.2 ohms but I could be way out. It would be really interesting to have an accurate measurement so if anyone has ALL of the following please post a reply:
1, A DC current clamp meter capable of measuring down to a couple of amps accurately. (If not WHY not!:))
2, a separate accurate multimeter capable of measuring millivolts.
3, a system on their MH which uses the standard non adapted charging system (No B2Bs)
4, The interest, time, etc to be arsed!
 
Meanwhile ... (in parallel to all this technical inquiry), back to my original puzzle. I've now purchased the 12v 30a charger, taken a new spur off an existing mains socket and successfully installed an additional CBE socket close to where I wish to mount the new charger. (All virgin territory this).
Two new questions.
1. I need to extend the red and black charging cables by up to a metre in order to wire the charger permanently to the battery. What gauge cable should I use. I assume it's quite critical.
2. Ideas to firmly secure the charger to the wardrobe wall please.
Thanks again!
 
The cables need to be at least the same or slightly bigger, and as for securing if it doesn't have mounting holes return it for one that has if possible.
 
RSD7a said:
Meanwhile ... (in parallel to all this technical inquiry), back to my original puzzle. I've now purchased the 12v 30a charger, taken a new spur off an existing mains socket and successfully installed an additional CBE socket close to where I wish to mount the new charger. (All virgin territory this).
Two new questions.
1. I need to extend the red and black charging cables by up to a metre in order to wire the charger permanently to the battery. What gauge cable should I use. I assume it's quite critical.
2. Ideas to firmly secure the charger to the wardrobe wall please.
Thanks again!
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Go a little bigger I'd say 2.5mm. OK for 20A which is actually all this particular 30A charger gives. I suspect the original is 1.5 and actually a little undersized.
 
merl said:
Go a little bigger I'd say 2.5mm. OK for 20A which is actually all this particular 30A charger gives. I suspect the original is 1.5 and actually a little undersized.
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Hi Merl (and others) The 2.5mm cabling has arrived. It's thin wall automotive and looks considerably thinner than the charger leads I'm going to extend. Should this kind of cabling be ok? Spec below.

Automotive Single Core 2.5mm2 Thinwall Auto Cable 29 Amp 12v 24v Thin Wall
Red ⋅ 1M ⋅ 2.5mm² (50/0.25) - 29.0 Amp
Returns accepted through 19 Apr 2023.
 
I got some thin wall for the self build, I wasn't happy and got normal stuff but mine was buried so I didn't want it rubbing through, your is in the open so should be okay I think.
 
Yes it's fine. The reason why it appears thinner is because it's automotive grade and designed for low voltage and has to a thinner insulation. Not important on your case, what's important is the size of the conductor.
 
Yeah the weedy ones will let you off paying if you nudge them, bigger ones are best left alone.

Sorry

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This will be small beer for many but a major, major leap for me to have taken a mains spur off an existing socket into the wardrobe, installed a new CBE socket and secured and wired in my new charger. Thanks to all who advised and pats on the back for me, freely accepted.
IMG_20230321_135617984.jpg
 
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I see what you mean about that thin cable you used to extend the charger leads, it does look quite thin! I'm wondering if they've sent you the correct cable.
When you stripped off the insulation from both the original and the new cables to make the join can you recall what the actual copper conductors appeared like in comparison to each other size wise?
 
It will slip out of the black strapping, there are mounting holes on the side for a alloy bracket, why did you not cut the plug off and wire it into the main fuse box, it will work as is mind you.
 
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