Lithium B2B charger

[GUMPY]

Has anyone fitted one to charge a Li battery in the van from the car and if so how did you wire it? I'm struggling with various possibilities.
I could just manage without one but depending on charge levels it's possible for the car to partly discharge the Li battery, not to mention I would like to limit the charge taken from the alternator.

 

[Buckman]

When towing doesn't the car help recharge the battery? If so, I wonder how it copes with having a lithium battery in the caravan and the car having a Smart alternator?

 

[JTQ]

When towing doesn't the car help recharge the battery? If so, I wonder how it copes with having a lithium battery in the caravan and the car having a Smart alternator?

Except there is voltage loss in pushing amps to the remote battery, plus the alternator will be modulating its output voltage to optimise overall vehicle fuel economy.
That whilst a Lithium technology battery is even more sensitive, and actually its critical, that the charging voltage is "right" , than it is for a LA battery.
Therefore somewhere there has to be some precision voltage regulation, ah, the very role of properly specified B2B devices..

 

[GUMPY]

When towing doesn't the car help recharge the battery? If so, I wonder how it copes with having a lithium battery in the caravan and the car having a Smart alternator?

Cleverly when I am towing my car switches from a Smart alternator to a standard 14.4v alternator which means it might charge the LiPo battery without a B2B charger but I would be reliant on the LiPo battery BMS to control the charging which is not good.
What I am looking for is a way to wire the B2B in so that the charger is not bypassed by the vans internal wiring.
Trying to find an accurate circuit diagram of the habitation relay circuits for my Elddis Affinity 554 is almost impossible.
The Elddis provided diagram doesn't even have the right equipment on it and only shows the external connections and nothing inside the CU.

Back to searching

 

[GUMPY]

Having searched high and low I have come up with this diagram that I am led to believe is of the PDU in the van.


Can anyone confirm that if I connect the charger input to CHG2 and the output to CHG1 the relays will switch the charger in and out depending on whether the car is connected or not? I will be adding a remote switch from the fridge circuit J3,4 to switch the B2B on and off with the ignition.


Am I mad?

 

[Jcloughie]

Above my pay grade. 🥵

John

 

[trevormonty]

Isn't car extra 12v connection designed to just run fridge while towing.

There will be Li chargers that will run off 12V supply with set max charge rate that you can use. Google DC-DC charger.
Run these chargers from fridge 12V supply and turn fridge off, trying run fridge and charge battery at same time is likely to fry something.

 

[RogerL]

Isn't car extra 12v connection designed to just run fridge while towing.

There will be Li chargers that will run off 12V supply with set max charge rate that you can use. Google DC-DC charger.
Run these chargers from fridge 12V supply and turn fridge off, trying run fridge and charge battery at same time is likely to fry something.

It's also designed to recharge the onboard 12v leisure battery

 

[ProfJohnL]

Having searched high and low I have come up with this diagram that I am led to believe is of the PDU in the van.

View attachment 6131
Can anyone confirm that if I connect the charger input to CHG2 and the output to CHG1 the relays will switch the charger in and out depending on whether the car is connected or not? I will be adding a remote switch from the fridge circuit J3,4 to switch the B2B on and off with the ignition.


Am I mad?

Without knowing what triggers the relays, its impossible to say if your idea is workable. Sorry

 

[GUMPY]

Without knowing what triggers the relays, its impossible to say if your idea is workable. Sorry

Looks like I'm going to have to spend an afternoon at the van with the multimeter 🤔

 

[GUMPY]

There are two supplies from the car
Pins 9+ and 13- are a permanent 12v supply for charging
And
Pins 10+ and 11- are switched by the ignition to run the fridge.

My hope is to use 9&13 to run the charger which will be switched on and off by pins 10&11.

Will investigate and report back🤔

 

[ProfJohnL]

There are two supplies from the car
Pins 9+ and 13- are a permanent 12v supply for charging
And
Pins 10+ and 11- are switched by the ignition to run the fridge.

My hope is to use 9&13 to run the charger which will be switched on and off by pins 10&11.

Will investigate and report back🤔

your reference to pin numbers I assume (but cannot be certain) related to the multiway plug on the car, however that does not tally with any of the connections references on the drawing.

 

[GUMPY]

your reference to pin numbers I assume (but cannot be certain) related to the multiway plug on the car, however that does not tally with any of the connections references on the drawing.

The pin numbers are indeed the numbers from the 13pin socket on the back of the car.
The previous diagram is allegedly of the inside of the PDU in the van there is no, that I can find, clear interface diagram between the plug/caravan and the PDU as none of the connectors in the caravan diagram are numbered.


I believe that the J numbers on the previous PDU diagram refer to the connectors above i.e J1,2 is pin 2 of the battery connector but since the drawing above has no numbers on it.........,.......

Hence the only way I can see of finding how is to trace the whole thing with a multimeter.

 

[GUMPY]

Spent time yesterday checking Voltages and Amps with the car and caravan.
Maximum charge rate with car connected to van is just over 5 Amps with voltage at 13.5 at the battery which is as high as it gets even on a mains charger until it's fully charged, I am happy with this. Only confusing bit is that voltage in the car is 14.3 so there must be some kind of circuitry* limiting the charge going into the battery, whether that is in the car or caravan I don't know. Whichever it is seems that I've saved £150 on a B2B charger.

* Could also be the length/thickness of cable between the car battery and the van battery causing volt drop. I will look further when it's not raining.

 

[JTQ]

* Could also be the length/thickness of cable between the car battery and the van battery causing volt drop. I will look further when it's not raining.

Very likely, if there is a current flowing.
If you recheck with the caravan's loads disconnected [probably the load is only the charge to battery?] then if you see the full voltage without the drop then indeed it's the cable drop under real life loads.

If the B2B features voltage boosting, then it is still worth having as it would lift the depressed voltage that reaches it, to its designed output voltage.

Some "better" caravan control/charging units incorporate that feature, eg Schaudt Electrobloc. Here that lifts even right down to 10point something volts reaching it, to 14.4Volts.

Your 13.5 Volts reaching the battery at "goodtimes", whilst just charging really will get nothing into the battery in realistic terms, IMO simply not worth being there.

The concept of B2B where the controller has not that feature [most of them], is a good one if recharging whilst towing is felt important.

 

[RogerL]

Spent time yesterday checking Voltages and Amps with the car and caravan.
Maximum charge rate with car connected to van is just over 5 Amps with voltage at 13.5 at the battery which is as high as it gets even on a mains charger until it's fully charged, I am happy with this. Only confusing bit is that voltage in the car is 14.3 so there must be some kind of circuitry* limiting the charge going into the battery, whether that is in the car or caravan I don't know. Whichever it is seems that I've saved £150 on a B2B charger.

* Could also be the length/thickness of cable between the car battery and the van battery causing volt drop. I will look further when it's not raining.

There's always some voltage drop - at 0.8v (14.3-13.5) I'd personally be content with that.

Can we assume that your figures were with the engine running at tick-over speed while connected to the caravan? If so it's worth remembering that the alternator voltage may rise when running at cruising speed, maybe as high as 14.8v, and the alternator output, in amps, may rise as well - but it's impossible to check those figures with ordinary test equipment.

 

[GUMPY]

The only "load " was the battery charging.
Even on a mains charger set at 14.2v the LI battery will hold the voltage down at 13.5v and take the maximum current available from the charger until it's fully charged and only then after the BMS has disconnected will the voltage rise. When connected to a 15 amp charger after 5 hours on charge the BMS reports an increase of 75Ah just as with a 10amp load after 5 hrs it reports a 50Ah drop in capacity. And yes I was sad enough to run a couple of full cycles on the bench before fitting it to the van.
Van is 10 miles away so not sure when I will get back there

 

[GUMPY]

There's always some voltage drop - at 0.8v (14.3-13.5) I'd personally be content with that.

Can we assume that your figures were with the engine running at tick-over speed while connected to the caravan? If so it's worth remembering that the alternator voltage may rise when running at cruising speed, maybe as high as 14.8v, and the alternator output, in amps, may rise as well - but it's impossible to check those figures with ordinary test equipment.

It was at tickover and at 2500rpm connected to the van. Voltage was pretty steady at 14.2/ 14.3 in the car and at the battery voltage was 13.5 and current 5 amps irrespective of revs.
Battery was monitored via the BMS over Bluetooth and the cars volts via a plug in voltmeter.
I am fairly content with it as it's only 0.8v which at 5 amps means that only 4 Watts are being dissipated somewhere in the system, less than a sidelight bulb🤔
New tool to use next time my ECU test program for the car reads battery voltage, current and SOH so can monitor what's happening there😉