B to B Charging loop - never ending charge cycle

DIY
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1

I am an electrical and controls engineer working with 400VAC and associated machinery controls systems 24 - 240vac, so I am not a numpty when it comes to electrical systems, but having recently acquired an RV I decided to upgrade the lead acid leisure battery to LiFePo4, so selected a Fogstar 280AH Pro along with their dedicated charger. This is my first experience of LiFePo4.

The vehicle original system uses a multi functional charger Redarc BCDC1240D. This combines the alternator charge and solar charge inputs and distributes to the Vehicle & Leisure batteries when the engine is running and leisure only when it isn’t.

This was a separate small B to B charger CBE CSB-2 that allows excess energy in the leisure battery to keep the vehicle battery topped off at max 4 amps. It turned on at a preset threshold of ~ 13.6v on the leisure circuit, and trickles the vehicle battery.

This device has a poor safety reputation so as part of my Lithium upgrade I replaced the CSB-2 with a Victron Orion Smart 12/12-18 B to B charger. Also with vastly more stored energy available, I felt this was good use of excess leisure energy.

All fine for 6 months until upon first using the RV after the Winter when the Vehicle battery failed. I assumed this was due to the battery itself not enjoying the high Start Stop engine load favoured by Ford transits, et al. I ordered a replacement and put it in the vehicle and checked the function.

I observed the new Victron was in Bulk charge mode, having set it up for AGM cycle via its blue tooth. As the battery was new I just assumed it need topping off.

However, upon checking it the following day it was still in Bulk phase. I wired in a DC ammeter to observe 14amps steady into the Vehicle battery. So by now it had already charged some ~150AH into the new battery (82AH) - or had it ?

I then observed the Fogstar Battery had ceased charging from its mains charger, even though it was demanding charge and was set to charge, it was discharging and down to 69%. I reset the Fogstar by turning the charge mode off and on again and charging from the mains charger re-started.

But the Vehicle battery continued to Bulk at 14amps from the Victron.

I then disconnected the Victron output and hooked up a separate mains battery charger. This also went to bulk but was limited to 7amps (capacity was 8amps), and for several hours stayed there, but then moved to Absorb, but would not move on to Float. The Vehicle battery terminal voltage was stuck at 13.3v, although it did slowly increase overnight up to 14.2, and occasionally the mains charger would briefly move to float mode.

I then disconnected the battery +VE with the charger direct to the battery and the new battery immediately went into float mode. Clearly a side load was acting, and this was likely the Lithium battery acting as a voltage source for the Victron, this forming an endless charging loop.

The Redarc has a voltage sensing input from the Alternator D+ terminal. It seems the Victron was now using the Lithium leisure as a power source to charge the Vehicle, but the vehicle was then putting power back to the Lithium due to the Redarc settings. Because the Lithium has ceased its own external charge, the whole loops cycle was being driven by a slow run down of the Lithium.

I think the ‘load’ absorbing this energy was the heat sink on the Victron and other flow losses in the leisure and Redarc.

I now wonder if the reason the Vehicle battery failed (was dying rather than dead) is because it has been force charging the whole system for months.

I also do not understand why this same loop was not formed by the far lower capacity CSB-2 B to B charger fitted by the RV maker. The RV is Ford transit based. I do have the RV charge system wiring diagram, which I am capable of reading.

I can’t understand why the Redarc, with the engine not running, would allow the Vehicle battery system to effectively provide the Lithium with the energy it has just sent to the vehicle battery charge circuit. Neither can I understand why the same issue did not occur before I fitted the Victron via the original CSB-2.

Now doing my head in, so help appreciated, and I understand I have several differing items expected to work together here.

Could this even be an Alternator fault as surely the D+ should go to 0V when the engine is not running. I have not tested for this yet - trying to work out the way forward to resolve this problem.

Thanks to anyone that can help me get my head around this.

Motorhome old PMW to MPPT with starter and leisure batteries, solar, alternator and mains charger!
2

All this text and i still struggle to understand which device is charging which battery. Maybe add a schematic if possible.

Its a question of activating voltages. Probably before the voltages were set high enough for the two devices to not trigger eachother.

If i understood correctly you have a Redarc DC/DC taking its input from the starter battery and charging the LiFePo. And a Victron Orion taking its input from the LiFePo and charging the starter battery. In order to avoid a charge loop you either need to set the engine shutdown detection (or its counterpart for Redarc) in such a way that both DC/DC chargers dont trigger eachother. Or you use the remote input, at least on the Victron, dont know if the Redarc has a similar input.

D+ only helps when its connected to the remote inputs.

3

The full diagram is not good as a simple working schematic. I will try to draw a flow diagram. This might help my own diagnosis process also.

4

I have come up with this. This is what I think is happening. Not sure what the status of the alternator control signal is yet.

RV unexplained charge loop.pdf (29.1 KB)

5

Is it a real D+ from the car?
Sometimes it’s just generated if the voltage of the starter battery is above xV.

6

I’m not sure the Orion is the best device to replace the CSB-2

Maybe a better choice would be a Victron cyrix,

Datasheet-Cyrix-Li-ion-120-A-EN.pdf https://share.google/RAUnX6OQox6Plu9gt

or a dedicated battery maintainer like the Ablemail AMT-12

AMT12-2 Trickle Charger charges Vehicle Battery from Leisure Battery with Solar Charger /Mains Hookup or only a Secondary Battery - Ablemail Electronics AMT12-2 Trickle Charger charges Vehicle Battery from Leisure Battery with Solar Charger /Mains Hookup or only a Secondary Battery - Ablemail Electronics

7

What I cannot understand is why the Victron almost maxes out its output, and why this problem does not occur with the CSB-2.

I still have the CSB-2 so time to do some experimenting. So I will find out what comes back on the Alternator D+ feed into the Redarc. As suggested I will look more closely at the Victron Cyrix - thanks.

Is there a Victron combination Charger that replaces the Redarc BCDC1240D ?

I am not convinced the RV maker’s designs are too clever, and their as installed wiring is simply awful - Wago’s everywhere, with a real snake’s wedding of wiring. I have done my best to improve the security. I found some fuses not shown on the wiring diagrams hidden in a box by the leisure battery. I have now placed all of these in an accessible fuse box, along with the 10a safety fuse from the former CSB-2 to the Vehicle battery common. I have also replaced the original 1.5mm2 cable with 4mm2, and increased the fuse to 20a to match the max 18a output from the Victron 12/12-18.

Just want to stop this damn loop, and just have the vehicle battery be topped up when it needs it, without it back feeding the leisure unnecessarily. I wonder if a simple voltage sensing relay would be better for this. It would be useful to understand more how the ‘Smart’ Alternator works - I will be interesting to discover if the D+ is a derived signal, rather than really from the “Smart Alternator“, and with the now massive Leisure capacity is a smart alternator necessary - just chuck excess charge as required into both batteries when the RV is running. An oil pressure switch could also tell the system when the engine is running, as could a tacho derived signal.

8

You would need to change to the CSB3-LT with your Fogstar setup as the CSB2 switches at too low a voltage, so would likely be charging the vehicle battery all the time, risking flattening the leisure battery

CSB3-LT car battery automatic recharging device | CBE CSB3-LT car battery automatic recharging device | CBE

There are better alternatives to this I think.

9

I removed the CSB-2 when I fitted the Fogstar. I would not out of choice fit anything CBE.

10

Clark

Yesterday I installed the AMT12-2B (bluetooth version) and the problem is completely resolved. It seems the Redarc multi input controller does simply look at the vehicle terminal voltage for its input engine is running signal. It does have a separate Alternator D+ input but the details of how this is used are about as clear as mud.

Anyway all sorted now and thanks for your reference to this device.

11

Good to hear you’re sorted Trevor.

From a confirmed Victron addict, I think that’s the only device out there that is better than Victron - for this specific application anyway….