lithium batteries, Charger and solar control

[TCG]

Hi Guys
i need some direction. looking to replace my hab batteries with Lithium. i have contacted Sargent who tell me i need to replace both the smart battery charger and also the solar controller. can any recommend these and also is it easy to change these.
Has anyone else done this on an autotrail

thanks

 

[Kannon Fodda]

I'm putting my faith in Vanbitz to do exactly this later this week.

Autotrail's electrics are a weakness of the MH as the Sargent kit is quite basic. The inbuilt charger profile on my EC176 is quite frankly a joke, a flat 13.8V charge of up to 12A. (whether on EHU or via the alternator) Combine that with a 75Ah lead acid battery and my PVC really struggled last weekend when the solar contribution was negligible. So nothing is really compatible with the Lithium, yet do to space constraints in a 5.4m long PVC, I'm limited that a single lithium battery will be better than doubling up the lead-acid (and oddly Sargent allow the lead-acid to be doubled up, and make leads for it, yet also say their charger is only capable of up to 120Ah). Big challenge is that everything 12V leisure seems to be routed through the Sargent which acts as the entire 12V system junction box and fuseboard, and also does all the 240V EHU stuff too.

The solar side is an easyish fix - Victron MPPT Smart Solar Regulator, should be a simple swap out for the existing controller.

Alternator charging whilst motoring along will need a B2B (Sterling or Victron). Unless I want to drive for hours and hours the max 12A of the Sargent would never refill the capacity of say 100Ah Lithium. Plus the B2B will have a proper charge profile for Lithium. I know, somehow, the existing relay wiring through the Sargent will need to be bypassed.

And then on EHU again there is a need for a different mains to 12V charger with a lithium profile, again bypassing the Sargent thing.

 

[ManTheVan]

As KF says above, Victron’s smartsolar MPPT is a very easy swap for whatever solar charger you currently have and it comes with the wonder of instant access to see charge level via an app on your smartphone.

You’ll also need, as he says, a B2B charger so you can charge the LiFePO4 on the move. I fitted a Sterling one (check Sterling’s clearance page to see if there is anything there to meet your needs). Sterling are incredibly helpful on the phone if you need assistance. The B2B will need a direct connection to your starter battery, so you may need to run fresh cabling for this. The 30A version I fitted needed 6mm2 cable, according to Sterling’s documentation on their site.

The LiFePO4 has been an amazing upgrade. We haven’t needed to hook up since installing it.

 

[RandallC]

An off the wall thought.

If a solar controller can provide the necesary charging profile for the LiFy then can you use one as a b2b. Given B2B unless using inverter tech to boost output will probably have the same volt drop & efficiency as a mmpt solar.

Think a PWM solar controller is a no no as it shunts rather than passes through

So would it work and which is cheaper?

If a mmpt controller can be used could you install a relay so when engine running fed from alternator, when not from solar panels. Admitted you loose solar input when traveling.

 

[ManTheVan]

Nice idea, but I think that the currents would be prohibitively high, wouldn’t they? Also, the MPPT controllers are designed to tweak the voltage and current output to suit the best charging profile of the battery and to maximise the output of the panels, so I’m not sure they would be the tool for the job.

The B2B is purpose-designed specifically for the function, so would be the best bet IMHO.

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[RandallC]

Agreed, was just a thought and without the resources, can't test the theory as it were.

Maybe someone has old stuff around that's just gathering dust who might fancy an experiment or two.

 

[Off da Grid]

Nice thought a good solar mppt controller could run 20 or 30 amps or more and would have the profile for lithium.
You could theoretically connect the alternator or leads from the start battery to the solar panel input.
I wish I had a spare mppt controller and lithium battery to try it out.

 

[eddie]

Nice thought a good solar mppt controller could run 20 or 30 amps or more and would have the profile for lithium.
You could theoretically connect the alternator or leads from the start battery to the solar panel input.
I wish I had a spare mppt controller and lithium battery to try it out.

The output voltage of the alternator would be too low to give you anything like the 20 - 30 amps

Much safer to simply use a DC - DC charger with a Lithium profile

 

[autorouter]

Many MPPT controllers, and certainly Victron ones, need an overhead of 5 volts above the battery voltage before they will start up. So the alternator would need to be 17 to 18V minimum, but most of them are not over 15V.

 

[RandallC]

Ahh not aware of this thought at worst was a PN junction voltage or 2. I.e. 0.6-1.2 volts.

as said unless the B2B uses inverter tech the best it can do is 0.6-1.2v less than the supplying battery. there has to be at least 1 blocking diode/MOSFET to prevent reverse current flow. UNLESS there is a relay OR it’s a normal function the current flows in both directions.

Mppt controller will block reverse flow as solar panels go low resistance in the dark and will flatten the connected batteries without a blocking diode.

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[eddie]

Unless you use a moon opelectric diode, to trigger a relay and switch the supply to the new range of Lunar panels, recently launched on the MHF Shop

 

[Raul]

Many in here do not understand the simplicity of a mppt solar charge controler.
I will try to explain as best as I can. It is a DC DC converter with a buck( cut) function. Does never ever raise the voltage from the input to the output. For that you will need a boost dc-dc converter. Therefore your input has to be higher than the output by few volts. When is in mppt mode, it sweeps the source of power, as intended for PV, I will sweep the PV and works out ultra fast how low it can pull the voltage without compromising on amps and works best volt amps combination for that given moment for maximum W, power.
You can unorthodoxly supply a input from stable power supply as a input, but the mppt will not work well on this combination. Of course you will need to meet min voltage. I have tested solar chargers on wind turbine generators, that are capable of high voltage to start it, but it will stall it very often.
To connect it to a Car/Van alternator and try to charge a battery, it will not work. First as others have mentioned already, the alternator is not capable to deliver the min working voltage. Even if it would , the mppt will put it on its nose quite quick by forcing it to max its voltage. You may be ok with a wind turbine regulator with a true buck boost regulator but they are 300-400 quid 30-40A if you find them. Best is to stick to B2B chargers that are designed for this precise purpose and are very good at charging most chemistries.

 

[RandallC]

Thanks Eddie for clearing that up, had completely forgotten about the mppt maximising current input as you describe. any idea what would happen to charge/current rates as the battery approaches Fully charged levels And how would the mppt controller respond to this?

 

[Raul]

As the battery gets full, the internal resistance rises, and amps drop ( see ohms law); so to push more current, you will need to raise the voltage. Since absorb is a constant voltage mode, the voltage is held constant, hence the amperage drop due to high resistance. You can not Over charge a full battery, unless you raise the voltage. The mppt just throttles back the power as soon as detects CV mode and is simply doing it, by shifting the power point on the V/I curve to allow only the necessary power needed for that moment.

 

[RandallC]

Agreed, which is in part my thought, at What stage of the charging process does the mppt controller go from max current in, (assume some current limiting capability or perhaps not) to voltage maintenance (floating)

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[Raul]

The solar charging is done in three stages: bulk( max power) limited by design or by controller. The rate you are bulk charging, dictates the voltage rise speed. High rate quick rise, slow rate slow rise, and optimum rate normal rise. The quicker you go through bulk( high rate), the longer you spend on absorb. Second stage is followed by absorb( constant voltage) at this stage once the battery reaches the preset absorb voltage on the controller, it holds that voltage until current reduces to almost nothing or preset tail current. If this function is NOT available, the controller has a built in algorithm and works out the necessary time in absorb mode. Once the absorb mode is done, it will enter the third stage of charging ( float), this is still charging but a very low rate. The float charge are two types: cycling and storage. The cycling is slightly higher as it has to cover eventual loads as well as caring a complete charging ready for discharge cycle. Storage can take its time as no loads or discharge are in due course, so the voltage can be lower.
As a analogy of this stages would be, your battery is a empty bucket. On bulk you fill it up with stones until full, then absorb you will further fill it up with sand until all spaces around stones is full again. Then, On float you fill it up with water to the brim. Once full it can’t take no more, the battery behaves like a resistor and it will waste any incoming power in heat. Give it to much(raise voltage) and it can’t dissipate it fast enough and goes into thermal runway.