Upgrading your caravan for lithium? 12V Guru explains how to make a BMPRO J35C system lithium-ready, with tips on charging, monitoring and compatibility.
Hi David,
My wife and I own a 2019 Jayco Silverline caravan which is fitted with a BMPRO J35, model C. With your experience with BMPRO I am hoping you can advise me of which direction to go.
I installed two lithium batteries from iTechworld before a recent trip to Western Australia. I was told that the batteries were a drop-in swap and that my charging system did not need to be changed. I now know that is not correct. The BMPRO model C does not recognise the lithium batteries, and it also has no capacity to receive charge from the car.
I have rectified this by fitting a REDARC DC-DC charger to my van. Because the lithium batteries do not show a voltage drop until they are nearly dead flat, the solar panels also did not provide charge. I have been advised that a model D will work and recognise and charge the lithium batteries? I would also like to know if the Bluetooth node 102 is compatible to monitor the battery status? Thank you in advance for your expertise.
Regards,
Russell Breguet
Hi Russell,
Yes, unfortunately it can be a bit of a minefield trying to bring together the right system to meet your needs and there is a fair bit of misinformation out there. Hopefully we can identify some key points here to make it easier.
Why lithium batteries need the right charging setup
Lithium batteries require proper charging profile to maximise their lifetime and your investment. Here’s why you should only charge a 12V lithium battery with a charger specifically designed for lithium batteries and not a standard lead-acid charger such as the BMPRO J35C.
Lithium batteries require proper charging
Lithium and lead-acid batteries require very different charging algorithms:
- Lead-acid batteries use a multi-stage charging process (bulk, absorption, float) and can tolerate trickle charging or being left on the charger
- Lithium batteries typically need a constant current/constant voltage (CC/CV) approach and do not benefit from trickle or float charging — in fact, it can damage the battery or reduce its lifespan
- Lithium batteries have an inbuilt battery management system (BMS). This is a set of electronics that monitors charge to the internal cells, cell voltages and provide a range of fault protections. A lithium-specific charger is often designed to work with the BMS, ensuring safe and efficient charging. A lead-acid charger may confuse or conflict with the BMS.
Steps to upgrade your caravan’s power system
It is possible to upgrade your J35C to the capabilities of a D version through the BMPRO upgrade program. Check out the website for more details. Your current unit needs to be removed and then sent away for an upgrade. As part of this, it receives additional warranty. The returned unit will then be set as lithium ready, and you will need to utilise the settings through the screen or app to ensure you set the right battery capacity so that it can effectively monitor battery state of charge.
It’s great that you have upgraded your DC-DC capabilities as the J35 series can only provide a trickle charge through its DC-DC input and can’t compete with the newer vehicle smart chargers to boost voltage and charge a battery properly on the go. I suggest that you install the BC300 external shunt to ensure that all current that goes into the battery directly from the DC charger is captured in the charging algorithm. In addition, the DC charger should be providing MPPT solar charging to keep the batteries topped up. If not, you can always wire the solar panels into the integrated BMPRO system which has its own proprietary charging algorithms.
Monitoring your system and final tips
In regard to the communications and brains trust of the system — the Control Node — it will need to be upgraded to the latest version of 103. This will also enable a range of new features such as the integration of gas bottle, temperature and tyre pressure monitor system (TPMS) sensors, increased Bluetooth range and more. This device is more of a communication device and will leave the battery monitoring to either the J35 or the BC300.
I trust this has helped in bringing together the story for a more intricate system that allows you more power options and extended off-grid camping options. One closing piece of advice is that as your system continues to evolve, try to bring together as many parts from one brand as possible, as this enables a higher chance of compatibility for the entire system, therefore, maximising your investment and opportunities.
Safe travels,
12V Guru
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