Do you take a mo­bile fridge/freezer with you on your trav­els? Or have so many gad­gets plugged into your ve­hi­cle that it drains the bat­tery? Yes, a dual bat­tery sys­tem of­fers a so­lu­tion – but there are a few things you need to con­sider.

Go! Camp & Drive - - Contents - Text Cyril Klop­per Illustrations Do­minic Wien­and

Ad­ual bat­tery sys­tem con­sists of a sec­ond (or third) bat­tery that’s con­nected to your ve­hi­cle’s al­ter­na­tor. The pur­pose of the aux­il­iary bat­tery is to pro­vide elec­tric­ity to your fridge or cof­fee ma­chine without drain­ing your main bat­tery. You can de­vise your own dual bat­tery sys­tem, or you can buy one of the many ex­ist­ing sys­tems and have it in­stalled in your ve­hi­cle.

How to in­stall it

The sim­plest way is as fol­lows: Con­nect the end of one bat­tery lead to the neg­a­tive ter­mi­nal of your main bat­tery and the other end to the neg­a­tive ter­mi­nal of your aux­il­iary bat­tery. Con­nect a sec­ond bat­tery lead to the pos­i­tive ter­mi­nal of the main bat­tery and the other end to an iso­la­tor. From the iso­la­tor there’s an­other bat­tery lead that runs to the pos­i­tive ter­mi­nal of your aux­il­iary bat­tery. Re­mem­ber that you need to add fuses to the pos­i­tive bat­tery leads in front of and be­hind the iso­la­tor. Now you’re ready to con­nect your favourite camp­ing de­vice to the aux­il­iary bat­tery. The rea­son you need an iso­la­tor is so that your fridge/ freezer won’t drain the main bat­tery’s power. The iso­la­tor can be a sim­ple switch you flip on and off your­self, to charge the aux­il­iary bat­tery. It is a has­sle, how­ever, be­cause be­fore head­ing off in the morn­ing you first have to drive for a few min­utes to charge your main bat­tery back up to 12,6 V; then you have to pull over to flip the switch, so the aux­il­iary bat­tery also charges; and when you ar­rive at your des­ti­na­tion, you have to flip the switch again to iso­late the main bat­tery so it’s strong enough to start your ve­hi­cle’s en­gine to­mor­row morn­ing. Sounds like a mis­sion. So to get the most out of a dual bat­tery sys­tem, we sug­gest an in­tel­li­gent so­le­noid. This de­vice au­to­mat­i­cally de­tects when your

main bat­tery is fully charged, and only then will it share the elec­tric cur­rent gen­er­ated by the al­ter­na­tor with your aux­il­iary bat­tery. If you want to mount the aux­il­iary bat­tery in your caravan or off-road trailer, you can’t use the stan­dard light con­nec­tor to charge the bat­tery. It’s not ro­bust enough to han­dle a charge cur­rent, and will prob­a­bly melt. Rather get 12 V, 120 Am­père An­der­son con­nec­tors to con­nect the bat­tery leads be­tween your tow­ing ve­hi­cle and your trailer. The in­stal­la­tion of a dual bat­tery sys­tem is some­thing best left to a qual­i­fied auto elec­tri­cian, but if you like to DIY you should con­sider get­ting a Na­tional Luna dual bat­tery sys­tem. It’s su­per-easy to in­stall your­self, and it de­liv­ers ex­cel­lent re­sults. We chat­ted to Peter Sle­ment, owner of Na­tional Luna, about their do-it-your­self sys­tem.

Asked and an­swered

Where should the aux­il­iary bat­tery be fit­ted? “Un­der­neath the bon­net is a good spot if you want to mount the sys­tem per­ma­nently, but Na­tional Luna of­fers a por­ta­ble dual bat­tery sys­tem that you put in the back of your SUV and take out at night if you want to use it in your tent.” Isn’t it risky to have a bat­tery inside an en­closed space? “Look, if you can smell the sul­phuric acid and hy­dro­gen in a bat­tery, it’s def­i­nitely time to re­place it. In any case, you should stay away from the old type of bat­tery, with plugs that con­stantly need to be re­filled with bat­tery wa­ter. A mod­ern, sealed bat­tery won’t emit toxic gases in your ve­hi­cle.” What kind of bat­tery is the best? “The sim­ple an­swer is that the aux­il­iary bat­tery should be as big as pos­si­ble (max­i­mum Am­père hours), be­cause you never want it to be­come com­pletely flat. At Na­tional Luna we pre­fer the ab­sorbent glass mat (AGM) bat­tery, be­cause it recharges quickly, op­er­ates like a deep cy­cle bat­tery, and re­leases a high load.” Is an al­ter­na­tor strong enough to charge all these bat­ter­ies? “Your mo­tor’s al­ter­na­tor is not a deep cy­cle charger. You’ll even­tu­ally re­alise that the aux­il­iary bat­tery al­ways draws the short­est end of the stick and will of­ten not be fully charged, es­pe­cially if you switch your ve­hi­cle’s en­gine off of­ten or drive short dis­tances. Be­sides that, you’ll prob­a­bly have to up­grade your ve­hi­cle’s stan­dard al­ter­na­tor; it’s also es­sen­tial to reg­u­larly con­nect your aux­il­iary bat­tery to a smart charger that mea­sures the con­di­tion of your bat­tery, and recharges it with the cor­rect cur­rent and volt­age.”

The pur­pose of the aux­il­iary bat­tery is to pro­vide elec­tric­ity to your fridge or cof­fee ma­chine without drain­ing your main bat­tery.

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