How do I keep my engine battery topped up?

QI have a Yuasa HSB019 battery linked to my Numax 110V leisure battery with a Battery Master unit. This, in turn, is supplied by a 110W solar panel controlled with a PWM charger unit.

The problem is that the vehicle battery has to be charged up every two weeks by a 50m cable to the charger to keep it topped up. I have ordered a new PV Logic MPPT Pro unit as I thought this might equalise the power better. I also intend to install a 1,000W power inverter to charge my e-bike battery. Would I now be better to change the leisure battery for an AGM one? Could the new battery be damaged by this proposal?

Ian Wilson

AI presume the Yuasa HSB019 maintenance-free battery is the engine starter battery and that your Numax is a 12V battery for the leisure electrics. The published data for Ca-Ca batteries suggests 14.1V, but also up to 14.8V to enable the recombination process to properly occur. So it is pretty tolerant to charging voltage.

The Numax L110 leisure battery is a wet-cell non-sealed battery.

Your PV Logic MPPT Pro solar regulator is an auto-selecting (12V/24V) model and is designed to charge two batteries, so I guess this is the reason you have ordered it.

As your main concern is about keeping the starter battery topped up by your solar panel, you could install a switch so that, when laid up, the output of your existing solar regulator is directed to the starter battery.

You will need to switch this back to ‘leisure’ when the

camper is once again in regular use.

As for e-bike charging, some of these chargers will work OK from a modified sine wave inverter, others will cause such an inverter to fry. The only sure way is to use a pure sine wave inverter capable of the starting load of your charger.

Most quote 100/240V AC input voltage and a running current of 0.7 to 1.4A for the 2A charger and double for the 4A charger. So, the worst case on start-up might be 672W. Most inverters have a peak rating well in excess of their continuous rating so I would go for a 500W or a 600W pure sine wave inverter.

But, be wary of claims for ‘surge’ power as not all live up to the claim of surge being double its normal maximum rating.

A reader had 2A chargers for his e-bikes

and, after finding some that did not work as claimed, he looked for another. He found a pure sine wave, 500W, 1,200W soft-start one on eBay for £49.99. “Well, to my surprise, it worked, so I wondered if it will charge two bicycle batteries with both transformers in use at the same time. And, yes, it did quite happily,” he reported.

This inverter is no longer available but there is a similar but more costly one here bit.ly/Sunshine500Winverter

If you want to use the inverter for charging the e-bike and perhaps a laptop every couple of days in the summer then your existing leisure battery arrangement should be sufficient. If you are planning extended off-grid winter camping then it could do with enhancing.

Clive Mott