Dual batteries for leisure system Renogy DC DC and factory Vsr

[Tandem2]

Hi Guys
Looking for clarification please?
I have a vehicle with a Vsr factory fitted that charges the AGM battery leisure battery. This battery is 80amp and supplies the internal lights and the van diesel heater. I have a dometic fridge that claims to use 80 watts on 12 volts. I have been unable to leave this on at night as the voltage drops too low and I have been un plugging it.
To provide additional usage time I purchased 2 x 120 w solar panels that add power to both the leisure and the starter battery via an Epever duo racer mppt solar charge controller. This rechargers the batteries and powers the fridge on sunny days but still doesn't allow the fridge to make it through the night. Due to the size of the AGM.
Then I managed to secure a lithium valence u27- xp12 which I plan to use just for the fridge. I have bought a Renogy DCC50S to charge the lithium circuit.
The aim is to be able to operate off grid for a few days at a time. I found this website and notice the comments about alternators being over stressed by Renegy high amp draws.
My questions are
1.since the Dc-Dc is connected to starter battery doesn't it only draw from the battery when it has more than 13.6 volts either when the engine is going or when it is fully charged and being topped up by the solar unit? The cable size I was going to use to connect starter battery to Renegy is 35mm I know it's over spec but it came from a welding friend.
2.I am planning to switch the Agm off if using the Renogy to lithium. Will manual kill switches be suitable ?
3. If I separate the solar panels and feed 1 to the Renogy it should throttle back the Dc-Dc to 25amps if have I interpreted the manual correctly? Daylight only.
4. If I uprate the cables to and from the Vsr to Agm could I fit a marine 2 battery selector switch and direct power from either the Agm or to the Dc-Dc and lithium circuit?
I am not able to fit the lithium in the Agm position and was looking to have dual leisure options to increase my off grid time.
Cheers all sorry if these questions have been answered elsewhere been concentrating on the Renogy ones. ?

 

[mikefitz]

From your system description I guess you are based in the UK or Europe.

A number of factors you may wish to consider

Vsr factory fitted that charges the AGM battery leisure battery

The alternator voltage at an AGM battery via a VSR is unlikely to fully charge the battery. The usual effect of this is gradual loss of battery capacity.

dometic fridge that claims to use 80 watts on 12 volts.

This sounds like an absorption fridge, a 12v compressor fridge is more efficient and most small leisure fridges of this type will use on average around 20 to 25 watts. Do you have more details on the fridge, model number?

notice the comments about alternators being over stressed by Renogy high amp draws.

The Renogy unit will draw around 55 to 60 amps from the engine alternator. Most current Euro vans have an alternator that can tolerate an additional load of this value. An older vehicle, say a historic VW van, would have a much lower limit. Vehicle details?

questions

1) If the Renogy unit is working correctly it will take power from the engine charging system when the voltage threshold is reached.
2) a suitable switch could be used , but see my later comments.
3) where there is solar input to the Renogy unit 25 amps max on solar or engine.
4) not too clear what you intend here, it all sounds over complex. see later comments.

I am not able to fit the lithium in the Agm position and was looking to have dual leisure options to increase my off grid time.

Is this due to the vehicle space restraints?

My comments and advice.

Start with what you have:

A RV vehicle with alternator charging ( alternator rating not known, need to be advised), a 80Ah AGM, a 138 Ah lithium, ( condition of batteries unknown), solar 2 x 120 watts, controller/chargers., VSR, DCC50S, EPever.
Loads: space heater, fridge 80 watts (continuous?), lights and phone chargers.

If indeed the fridge is a constant 80 watt load that's almost 2000 watt hours a day and cannot be met with 240 watts of solar. Perhaps just about doable with some driving hours. Over night, say 10 hours at 80 watts, 800Wh, OK for the lithium, but still need charged up the next day.

Advice:
Unless you are able to increase the solar and perhaps battery capacity, or unless you can drive for some time each day you will not have enough energy to power your system with the existing fridge.

Solutions:
1) Replace the fridge with a more efficient compressor 12v unit
2) Replace the VSR with the DCC50 (with suitable cables) and connect to the lithium and the AGM (the batteries in parallel).
3) Connect the EPever to the leisure battery pair only ( consider the AGM and lithium as one big hybrid battery)
4) Set all chargers to lithium charge profile.
5) Add more solar panels.

The hybrid battery concept with an AGM and lithium battery in parallel is used by some professional RV builders. The lithium offers fast charge and does most of the work driving loads, only when the lithium battery falls to about 20% capacity does the AGM start to contribute.
If you are unhappy with the 'hybrid' concept, junk the AGM and just rely on the lithium.

Mike

 

[Tandem2]

From your system description I guess you are based in the UK or Europe.

A number of factors you may wish to consider

The alternator voltage at an AGM battery via a VSR is unlikely to fully charge the battery. The usual effect of this is gradual loss of battery capacity.

This sounds like an absorption fridge, a 12v compressor fridge is more efficient and most small leisure fridges of this type will use on average around 20 to 25 watts. Do you have more details on the fridge, model number?

The Renogy unit will draw around 55 to 60 amps from the engine alternator. Most current Euro vans have an alternator that can tolerate an additional load of this value. An older vehicle, say a historic VW van, would have a much lower limit. Vehicle details?

1) If the Renogy unit is working correctly it will take power from the engine charging system when the voltage threshold is reached.
2) a suitable switch could be used , but see my later comments.
3) where there is solar input to the Renogy unit 25 amps max on solar or engine.
4) not too clear what you intend here, it all sounds over complex. see later comments.

Is this due to the vehicle space restraints?

My comments and advice.

Start with what you have:

A RV vehicle with alternator charging ( alternator rating not known, need to be advised), a 80Ah AGM, a 138 Ah lithium, ( condition of batteries unknown), solar 2 x 120 watts, controller/chargers., VSR, DCC50S, EPever.
Loads: space heater, fridge 80 watts (continuous?), lights and phone chargers.

If indeed the fridge is a constant 80 watt load that's almost 2000 watt hours a day and cannot be met with 240 watts of solar. Perhaps just about doable with some driving hours. Over night, say 10 hours at 80 watts, 800Wh, OK for the lithium, but still need charged up the next day.

Advice:
Unless you are able to increase the solar and perhaps battery capacity, or unless you can drive for some time each day you will not have enough energy to power your system with the existing fridge.

Solutions:
1) Replace the fridge with a more efficient compressor 12v unit
2) Replace the VSR with the DCC50 (with suitable cables) and connect to the lithium and the AGM (the batteries in parallel).
3) Connect the EPever to the leisure battery pair only ( consider the AGM and lithium as one big hybrid battery)
4) Set all chargers to lithium charge profile.
5) Add more solar panels.

The hybrid battery concept with an AGM and lithium battery in parallel is used by some professional RV builders. The lithium offers fast charge and does most of the work driving loads, only when the lithium battery falls to about 20% capacity does the AGM start to contribute.
If you are unhappy with the 'hybrid' concept, junk the AGM and just rely on the lithium.

Mike

Hi Mike
Thanks for the reply I am in the UK
Is there a reason that a VSR unit is unable to fully charge an AGM battery {House} ?(I have a battery charger in the circuit which can be used on shore power )and the AGM is also charged by the Duo Racer from the 240 watts of solar panels.

The fridge is a dometic absorbtion fridge model RC2200EGP 12 volt 240 volt and gas powered. It is 41 Litres volume.

The alternator is not a smart version as the vehicle is a VW T5.

I have purchased the Renogy DC DC 50Amp charger with a view to charging the lithium and connecting it to the starter battery. I thought the Renogy has to be set up to the battery type so would ouput it to the Lithium profile due to the charging profile (bulk, constant, float then equalisation) I thought i had to keep the battery types seperate [ although i came accross a suggestion on a boat forum to have Lead for starting/ cranking loads and lithium for long constant voltage in a combined circuit ]

I currently have a a single leisure AGM under the passenger seat. The Epever tops that up when parked and then uses the surplus to keep the starter battery which is also lead topped up.
The loads are the fridge, lights, phone charging and a diesel powered factory fitted cab heater.

Do I need to take the DCC50S cables to the starter battery through the firewall and connect to a busbar and circuit breaker? which would be in addition to cables from starter battery to VSR to Leisure( House) if not going for a hybrid solution. These cables are in place already.
the additional cables both +Ve and -Ve 35mm or can they be attached to a switched feed going to the Leisure/ House battery 3 position switch (off, batt 1, batt 1 + 2, batt 2). The location of the lithium is to be in the rear of the vehicle near the electrical hook up location and shore power fuse box.

I hope this helps.

 

[mikefitz]

AGM batteries typically need a higher voltage than the alternator can deliver, however the solar charger maybe able to make up the shortfall.

Have you tested the valence u27- xp12 and are aware that it has no real BMS protection without the external factory electronics?

With the existing solar, whatever you do, unless you drive for some time each day or have mains power hook up there will not be enough input power to drive the fridge. Why cannot you run it on gas, it is the intended primary energy source for this type of fridge?

One thought would be to fit the DCC50 near the lithium battery and run a cable from the AGM to the DCC50, use the metal body as a negative return, but the Epever solar charger connection gets a bit messy since any voltage rise in the engine battery or the AGM due to solar, will trigger the DCC50.

The VSR is most likely bidirectional so even if the connection to the DCC50 is taken of the alternator there could still be a problem.

The DCC50 is not the best unit for this situation since there is no disable input. A solution is a fit a 200A power relay activated by key on in the cable feed to the DCC50.

OK this may work.
Fuse at the AGM positive then cable to 200A power relay than to the DCC50, DCC50 to lithium battery,

Epever outputs, one to the starter battery, ( it will also charge the AGM due to the VSR), other output to the lithium.

To be honest this is all somewhat of a unnecessary mess of a solution caused by incorrect mode of operation of an absorption fridge and purchase of chargers/batteries that do not readily integrate into the system.

I am a little worried that the Valence u27- xp12 may not be compatable with the DCC50 charge voltages.

Mike

 

[Q-Dog]

Run the fridge on propane, or on 240 mains when available. Only run on 12 volt when you have sun or are driving and charging the batteries.