SUPERCHARGING YOUR MOTORHOME: BATTERIES
For many, a holiday in a caravan or motorhome offers the opportunity to spend some quality time “off grid”. The chance to hitch up and head off to wherever your fancy takes you. To live a nomadic lifestyle, if only for a short while, and leave behind the strains and stresses that dominate modern life. Sounds idyllic, right?
But stress isn’t the only thing you’ll leave behind. High-powered hairdryers, coffee machines, pressure cookers, air conditioning, computers… All energy-sapping everyday appliances that have no place in your temporary-home-on-wheels. Or do they?
This summer, I spent six weeks travelling around France and Spain with my family in our Hymer B668. It’ll come as no surprise to those that know me, that I spent a large proportion of that time working. For the most part, we chose to forgo the relative luxury of campsites (and their patchy electrical hook ups) for a more authentic off-grid experience. It was therefore essential that our motorhome could consistently meet our (ahem, my…) huge power demands.
The good news? My family and I utilised high-powered appliances throughout the trip without ever worrying we’d be stuck for power. I’m talking air conditioning, ice machines, film projectors, hot plates – the works! And here’s how we did it…
Lead-acid vehicle and leisure batteries are the default with most motorhomes. Not only are lead-acid batteries extremely cumbersome (not ideal for vehicles with stringent weight limits!), they perform poorly.
Let’s consider my wife’s trusty Dyson hairdryer.
The equation for working out power required is: Amps (A) x Volts (V) = Watts (W).
Leisure batteries in motorhomes are typically 100 amp-hour (Ah). The hairdryer in question is a 3 kW device (or 3,000 watts). Plugging the hairdryer (3 kW) into a mains sockets (at 230V AC) would result in a 13 amp draw (3kW / 230V = 13A).
By contrast, plugging the same hairdryer into a 12V DC leisure battery, would result in approximately 250 amp draw.. Typically, you can only draw half the capacity from lead-acid batteries before the voltage drops and they become useless. By withdrawing power at 5 times the recommended rate, the device would only work for a couple of minutes, and likely cause lasting damage to the battery.
So, what would I recommend instead?
Now, it’s important to note that lithium batteries are eye-wateringly expensive. For a set-up like mine, you could be looking at five figures. However, they can last for decades and are considerably lighter than their lead-acid counterparts.
Lead-acid batteries only have a limited number of cycles – the amount of times you can charge them up and discharge them before they start dropping off. If you use a hairdryer every day, you’re not going to get much out of the battery before you’ll need to buy a new one.
If you’re comfortable with the large initial outlay, then lithium batteries can work out more cost-effective over time. It’s the “buy nice, not twice” mentally that I employ when purchasing any big-ticket item.
For my motorhome, I ripped out the standard leisure battery and installed a bank of lithium ones. I use a type called LIPO4, which is safe for habitation areas (i.e. you can sleep atop of these bad boys and be perfectly safe).
Whilst you can discharge lithium batteries at 50% of their capacity, you can charge them at that rate too – a big benefit when you use as much power as the Lambs do. If you were to drain it down to 0% (which is extremely unlikely), you can charge it at 50 amps an hour, meaning it could go from completely dead to fully charged in just two hours.
We have six 150 Ah lithium batteries in our motorhome, so that’s 900 Ah total usage - 15 to 18 times more power than you would usually have. 900 Ah means we can draw a maximum of 450 amps, which comfortably meets the requirements for the aforementioned coiffure perfecter.
But how do you connect a hairdryer to a battery in the first place?
For that, you’ll need an inverter: a device that sits between the device and the battery, and converts DC electricity to AC electricity.
For low-power items, like laptop chargers, a small inverter is fine. But as soon as you want something more powerful you’ll need something much bigger. I chose a NDS 3000W Pure Sine Wave Inverter.
The inverter plugs into a priority switch, which prioritises power from the “outside” (AKA the national grid). If you’re not on hook-up, it switches automatically to the inverter. The result? All sockets inside the motorhome work just as at home – seamless power, 24 hours a day.
But with all batteries, comes the question of charging.
There are three different methods of charging that I use:
1) Mains hook-up
This is the obvious one, which almost all caravans and motorhomes benefit from. We have two chargers that charge from the mains at 50 amps each. At this rate, it would take 9 hours to get back to full capacity.
2) Solar power
We have 700W of solar panels on the roof. On a reasonably sunny day, you can expect 600W (40 amps). It would take approximately 22.5 hours (3 days of glorious sunshine) for a full charge. When at home, I leave the motorhome on the driveway with the panels doing their job ready for our next weekend getaway.
3) A battery-to- battery (B2B) charger
The B2B charger goes in between the lithium battery bank and the alternator. It simulates the load on the alternator, drawing current from it and feeding it into the batteries. I have two of these chargers, which can be plugged in whilst driving. I also upgraded our alternator to one with a greater capacity to power the B2B chargers in addition to all the engine electrics.
Now, I’m not going to lie – this is an extreme set-up. Everything is doubled up. For most people, 200 Ah would be plenty, perhaps doubling to 400 Ah to be on the safe side. 900 Ah is taking things more than a couple of steps further.
For me to be able to relax on this working holiday, it was important that I had 100% confidence in the system. This set up offered a fast-charging solution with plenty of capacity, and back-up options in case something stopped working.
Or, for those - like me - who enjoy a formula:
Lithium batteries + solar panels + B2B chargers = total peace of mind.