Smart alternator and BMS

[discomatt69]

I have a older redark DC-DC charger in the camper, since going from the D1 to the D4 it doesn't charge nearly as fast. I rang Redark and there response was I needed there latest and greatest at a massive cost. Something I am not that keen on doing as the old one has all the functions I want and if need be I can live with the slower charge.
The question of the brains trust is, Can the BMS / smart alternator be turned off the same as a Ford Ranger and a few other cars?
Or is there another way around it to get constant voltage to the DC-DC

[DiscoJeffster]

Just throw the thing out and connect it straight up to the car. Once it’s directly connected, the BMS will see the battery directly and keep the voltage up until they’re all fully charged.
I have mine directly connected (haven’t got a Traxide as yet) and I never have an issue with the camper being charged.

[Tombie]

Matt. How are you getting the power to the trailer?

[discomatt69]

I am definitely not throwing out the DC-DC, its a multi stage charger that keeps the batteries in top condition, it regulates my solar set up way better than the cheap regulators that come with solar panels, it charges from car, solar and 240v,mains or generator. It tells me SOC, time till flat and full, temps and draw rates.

The D4 already had the Anderson plug wired to the rear by the previous owner, not sure of cable size but will double check it. After buying the car I checked the voltage at the plug and it was over 14 so all good. Will double check voltage and size.

Last trip to SA the batteries were full when I got home but after a trip to Tocumwal, 280km from home, the batteries were still at 30% when we got home. They were very flat when we left due to 3 days of cloudy weather, I didn't check the voltage but the camper fridge was faulting and the low voltage alarm did go off when we were packing up. The camper has 170 amp hours.

I guess what I need to do is check that I am still getting good voltage to the Anderson plug after the cars battery is charged. I posted a simular question on Earth in a electrical thread and Tim said the cars BMS can not be turned off like some other cars. I have my head around the electrics and workings of my D1 but this car is like a space shuttle

[DiscoJeffster]

The BMS charges my 200ah of camper batteries fine directly connected to my alternator (at the battery). They’re charge to 100% in a few hours. Maybe bypass the DC charger for your car link and retain it for your camp setup for solar?
The BMS is more than capable of charging and managing the camper’s batteries and the car’s one.

[drivesafe]

Hi Discomatt, with your 170Ah of house battery capacity, you have nearly 140Ah available.

So if your house batteries are low, and you, I am assuming, have a 20 amp DC/DC device, you will need to drive for at least 8 hours to get them up over 95%, not fully charged but over 95%.

Your D4 will achieve the same level of charge, not fully charge but over 95% in less than half that drive time.

And you do not have to turn the BMS off to achieve that sort of fast charging time.

[Mike57]

I just want to check that I have got this right.

I have an Optima AGM in the back of the car which only gets added when i put the fridge in. i have a variable voltage sensing relay to protect the main battery and a 6B&S feed from the main battery via the VSR down to the back protected with a 50 amp circuit breaker. Currently I have a Redarc DC to DC charger in the circuit because originally I used to charge this second battery from the Aux socket down the back and I wanted to limit the charging current. Now I have the higher current feed I was going to upgrade to a 20 amp DC to DC charger but what you are saying above is that i don't need that and I can just connect the second battery directly to the main battery via the VSR? The cars charging system will reduce the current flow when the second battery is full and will not try to overcharge the main battery in the meai time (if that is possible).

Is that correct?

[discomatt69]

Yes that is correct you do not need a DC-DC in the back of the car, to keep the battery in top condition though you will need to put it on a multi stage charger every now and then.
I only run the DC-DC for all the extra functions I get out of it when base camped and in storage at home, when driving a DC-DC is not really required as the cars system keeps the batteries at 95-97% full with the alternator. Only a slow trickle charge from an multi stage charger charges any battery to 100%.

My understanding of battery charging only

[Tombie]

I just want to check that I have got this right.

I have an Optima AGM in the back of the car which only gets added when i put the fridge in. i have a variable voltage sensing relay to protect the main battery and a 6B&S feed from the main battery via the VSR down to the back protected with a 50 amp circuit breaker. Currently I have a Redarc DC to DC charger in the circuit because originally I used to charge this second battery from the Aux socket down the back and I wanted to limit the charging current. Now I have the higher current feed I was going to upgrade to a 20 amp DC to DC charger but what you are saying above is that i don't need that and I can just connect the second battery directly to the main battery via the VSR? The cars charging system will reduce the current flow when the second battery is full and will not try to overcharge the main battery in the meai time (if that is possible).

Is that correct?

As long as your VSR cut in and out voltages are suitable.

[Graeme]

The cars charging system will reduce the current flow when the second battery is full and will not try to overcharge the main battery in the mean time (if that is possible).

Is that correct?

Each battery will reduce the charge that it accepts as it gets close to its fully charged state, rather than the alternator limiting charge. If sufficient current is available, perhaps limited by the alternator's capacity or the sometimes reduced current by smart charging, both batteries will charge at their fastest possible rate. Some batteries will accept higher currents so get to their "fully charged" state sooner - not necessarily the primary battery.