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Replacing Charger and Power Supply in Jurgens Explorer

  • Aubrey Penderis
    Aubrey Penderis on

    Good day

    I would like to replace the Hercules 20 Power supply in my Explorer.

    I want to make up my own 220V DB box with circuit breakers and install a fuse box for 12V feeds.

    I do have a deep cycle battery in the van that charged by a National Luna 5A Charger.

    I would like to replace charger with maybe a Victron 220V charger with integrated Solar Charge controller and Bluetooth connection to a app to monitor charging.

    I am also goung to replace battery with Lithiuum battery

    What chargercan you recommend?




    Aubrey Penderis


    Fyko van der Molen
    Fyko van der Molen on

    One fact that the plague of loadshedding has made painfully obvious is how bad lead-acid batteries actually are.

    At stage 4 a heavily loaded UPS can experience 3 cycles per day (a cycle being where the battery is discharged to 50% of it’s nominal capacity). At this rate it takes a little over 3 months to run up 200 cycles and, yes, after 200 cycles the battery is shot.

    The reason car batteries last 3 or 4 years is that a typical start-up cranking takes less than 1000 Ampere/seconds out of the battery, which is under one third of one Amp/hour. And this is immediately put back once the engine runs.

    If you’re going to cycle your caravan’s battery, rather than keep it permanently on trickle charge at home or away, then lithium is obviously the route to follow. I’m still learning about lithium derivatives every day, but we all know that there are two sins that will murder a lithium cell in short order:

    1. Overheating.
    2. Overcharging.

    Both of which fall under the purview of the charger.

    In a series stack a single charge current flows through all the cells in the stack, which means the weakest cell gets overcharged while the stronger cells are not yet fully charged. This is why each cell in the stack needs to be individually charged. This much everybody knows. But how this plays out while the battery is being simultaneously discharged is not all that clear.

    One thing is very obvious though. The success of the venture is entirely dependant on the quality of the charger.

    I have never used or owned a Victron charger, but I have read the literature through and through. They make quite a big deal of their supposedly superior charging algorithm making use of Peukert’s equations.

    Peukert’s equations are simplistic, unidimensional and inadequate estimations, which have very little relevance in the modern lead-acid context and are absolutely no relevance in the lithium context at all.

    Therefore I’d be extremely suspicious of any manufacturer that tries to blind the peasantry with that kind of pseudo-science.

    So, not much of an answer (but maybe the only one you’re going to get), my advice is: do lots and lots of homework on the charger issue, and your lithium venture can be a success. I’m getting better educated on the lithium subject every day, and if I learn something useful I’ll be sure to share it.


    Simon Tasman
    Simon Tasman on

    Hi Fyko.
    I think the OP refers to a LiFePO4 battery which does not have the strict charge rules that pertain to lithium ion batteries.
    They don’t overheat and you can charge the whole stack in one shot.

    Fyko van der Molen
    Fyko van der Molen on

    Hi Simon,

    You’re quite right. But many people think that changing from SLA to LiFePO4 is similar to say changing to a low-energy light bulb. In fact SLA and LiFePO4 are not plug compatible – there are huge differences. Not that you shouldn’t make the change – it’s just a bigger change than you thought.

    Because of the limited charge/discharge cycles available to an SLA battery the system is designed to keep them fully charged as much as possible. A caravan battery charger is actually a 13,8V float charger that is capable of producing a large current. When mains power is connected it keeps a 13,8V float charge on the battery while at the same time providing 20 Amps of current to connected loads. The float charger also compensates for self-discharging, could be as high as 1% per day.

    When the input power source is removed the battery will enter a discharge phase to keep the loads powered, but as soon as the destination is reached, and the van is connected to the resort’s mains, the float charger immediately starts to restore whatever was taken out of the battery during the journey. The permissible charge rate is up to 0,3C, but this probably won’t be attained with a charging voltage limited to 13,8V. Bear in mind that the charging voltage will also be applied to the loads, some of which might be adversely affected by a high charging voltage being applied to them.

    Because of the damage that results from excessively discharging an SLA battery many of the more sophisticated loads such as fridge controllers disconnect themselves when the battery voltage becomes critically low. Other devices such as lamps and pumps will quite happily discharge an SLA battery to destruction.

    A LiFePO4 battery on the other hand must never be float charged. It should be charged to 0,95C and then put away and be forgotten until needed. There is no significant self-discharge in a LiFEPO4 battery. In a LiFePO4 installation there should be a dedicated high quality charger dedicated to constant-current charging of the LiFePO4 at a rate between 0,5C and 1,0C. There should then also be a 12V power supply capable of delivering at least 30A to power the loads such as the fridge, water pump, lights etc.

    When on mains power the charger should charge the LiFEPO4 battery to 0,95C at a rate of between 0,5C and 1,0C and then disconnect. The battery will then remain isolated entirely. At the same time the 12V power supply will attend to the needs of the loads in the caravan. Any solar panels will be inactive during this time.

    When there is no input power the LiFEPO4 battery will be connected to the loads previously served by the power supply as long as the State of Charge remains above 0,05C. When that low limit is reached the controller will disconnect the loads from battery A and connect them to battery B, if such a thing exists. If not they stay without power from that time.

    Assuming battery B is now connected to the loads then the solar panel(s), which will each produce a charge rate of around 0,05C, can start charging battery A, and keep doing so until the charge voltage indicated that the charge level is at 0,95C, at which point the battery will be disconnected and consigned to dormant storage.

    Once mains power is again available, any battery being solar charged will be transferred to the charger for the cycle to be completed, the solar panels isolated, and the DC power supply brought back to driving the connected loads.

    Using this type of implementation it will potentially be possible for the LiFePO5 batteries to fulfil the entire 5000 cycles that they are theoretically capable of. Obviously no such controller exists yet for caravans, but we have one in the works that we’ll make available privately in due course.

    Simon Tasman
    Simon Tasman on

    What does “available privately ” mean?

    Fyko van der Molen
    Fyko van der Molen on

    Implementing such a power management system is a lot simpler than you might at first think. In fact you can achieve 60% of it with just one relay.

    The 12V 20Amp power supply that will power all your 12V loads when the mains supply connected is found in the Chinese supermarket for less than R500. It connects straight to the incoming mains – when the main is on you have 12V power.

    The LiFePO4 battery is permanently connected to its charger, which in turn is permanently connected to the mains supply as well. The charger should be dedicated to LiFePO4 batteries rather than an attempt at one-size-fits-all, which is probably going to be a kludge.

    The charger should have a Stage 1 where a constant current of 0,5C (say 50A) is applied until the voltage reaches 14,6V. After that Stage 2 should apply a continuous 14,6 volts until the current drops to 0,05C. Stage 3 should discontinue any charging.

    The single relay is a SPDT device with a 30A contact capacity that is available at MIDAS for about R50.  It selects the power source from which to drive the 12V loads. The relay is pulled by the 12V from the 12VDC power supply. When the mains supply is on the relay routes power from there to the loads, when the mains is off the relay drops and connects the battery output to the loads.

    That’s 60% of the job done. Now you have to prevent excessive discharge of the battery and integrate the solar panels into the system.

    A LiFePO4 cell is considered completely discharged when its voltage drop to 2,5V. A 4-cell stack should therefore never drop below 10 volts. Our WaterWatch water meter has a voltage monitoring and low-voltage alerting capability. It will sound a buzzer when the supply voltage drops to 10,5V for LiFePO4 and 11,7V for SLA batteries. This will provide plenty of warning that the battery is just about exhausted.

    To totally disconnect the battery from ALL loads when it reaches a critically low charge we cannot do just yet, but we have in the works a low-cost domestic circuit breaker modified to allow an external device to trip it with a low-voltage impulse.

    This leaves only the solar panels to be integrated. A similar automotive relay as used above should connect the solar source to the battery when the mains power drops out. To prevent the solar from overcharging the battery it should be connected through a 10A buck regulator that can be adjusted to deliver a constant voltage of 14,5V. This will not allow the solar to charge the battery above 95% at any time, so it can stay connected indefinitely.

    Why private?

    While this is a simple and effective solution to getting a lifetime of service from a LiFePO4 retrofit, it certainly is not for everyone. There’s a minimum level of knowledge and workmanship needed from the owner without which such a project is unlikely to be successful, despite our best efforts at assistance So we work on referrals and word of mouth.

    Simon Tasman
    Simon Tasman on

    I’m not doing this conversion to the lithium battery myself. I’m helping my neighbour with it. He’s only got one LiFePO4 battery which cost him more than R4k, and so far we’ve followed your suggestion and it’s working just as you said it would
    He’s got one of your water meters that needs the voltmeter added.
    It would really be nice if it could also do the undervoltage cutout that you mentioned.

    Fyko van der Molen
    Fyko van der Molen on

    We do in fact have a Low Voltage Disconnect capability. But it uses a more expensive uncoupling device and most people don’t want to pay the R600+ that the thing costs. They’d rather take a chance on wrecking the battery.

    If you want to upgrade that unit you know where to send it. Just put a note inside that says LVD and I’ll know what to do.


    Simon Tasman
    Simon Tasman on

    We’re making pretty good progress.

    Outstanding items are the low voltage cut-out, and we can’t find a solar regulator that will deliver constant voltage at 14,5V.

    Fyko van der Molen
    Fyko van der Molen on

    Hi Simon,

    It’s essential that you have the right solar panel regulator. Don’t use one of these mass-produced one-size-fits-all with obscure function. I’ll make one for you no problem.

    The low voltage disconnect(LVD) is a bit more difficult. There are plenty of devices on the market – all of them useless for one reason or another.

    For maximum elegance I want a high-current switch that needs no power either when it’s on or when it’s off. Something like a domestic circuit breaker with an external remote control facility. Domestic CBs are very difficult to adapt because the current-sensing coil is very compact being made of only a few turns of thick wire. A low-voltage bobbin is very hard to fit in such a small space.

    What we’ve been doing instead is use a domestic earth-leakage CB – a lot more expensive, but adaptable with some ingenuity. The internal electronics are entirely oriented towards AC operation and cannot be adapted to a DC environment. However if you throw out all of the internal circuitry, including the solenoid which needs the internal amplifier to work, and attach an external solenoid, you can remote control it quite nicely. Ingenuity being a big part of this. I’ve had good success a Veti ELCB which costs about R450, but needs a few other bits and pieces to make a viable device.

    In the short term you can do without elegant LVD while you get everything else sorted.


    Simon Tasman
    Simon Tasman on

    If an LVD can help a LeFePO4 battery last 25 times as long as an SLA equivalent then that’s a potential saving of about R50k in today’s money.
    Worth a bit of expense I’d say.

    Fyko van der Molen
    Fyko van der Molen on

    For Low Voltage Disconnection (LVD) we’re delivering this unit now:

    It’s made a little bit pricey because it uses an ELCB for switchgear. But as you say spending R800 or so to save R50,000 makes good sense. So far this unit works perfectly, though we are looking around for something less costly. There’s a good chance we’ll stay with this format for the time being.

    The breaker trips 11,8V with SLA batteries and 10,0V for LiFePO4. All of the measuring and control is contained in the WaterWatch unit, which starts to give an audible low voltage alarm from below 12,0V for SLA and 10,5V for lithium.

    Voltage recovery will silence the alarm buzzer but once the breaker has tripped it needs to be manually reset, obviously. You can override by resetting the breaker while the voltage remains low (in case you need to do open heart surgery or something similarly urgent). Or you can pull out the cable to the breaker and defeat the system that way. The breaker has a 63A switching capacity.

    Josef Konrad
    Josef Konrad on

    This is a very interesting discussion. But maybe it should be in its own thread since it has moved far away from the OP’s initial question.

    One thing I think should be doubly emphasised:

    The original charger is a 13,8V float charger, albeit with a high current capability. That means that any connected load will not receive more than 13,8V at it’s supply input.

    However a smart charger will probably, at the beginning of the charge sequence produce for a time, a 200kHz de-sulphating frequency, followed by a constant current phase where the charge voltage may reach 16,5V. In the original Jurgens configuration where the battery is charged with the loads connected this may be bad for some of them.

    If you’re going to change to an aftermarket charger then you should have a means to disconnect the loads while the charger produces anything other than DC at max 13,8V

    Fyko van der Molen
    Fyko van der Molen on

    Driving loads from the battery while it’s being charged by an algorithm-driven charger would totally confound the logic.

    For instance the transition from Stage 2 (constant voltage phase) to Stage 3 (float charge) with an SLA charger is determined by charging current. If there’s extraneous currents flowing through connected loads then that current will never be detected, and the charge sequence will fail.

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