Date:         Mon, 4 May 1998 21:00:32 +0200
Reply-To:     "J.W.Brier" <Jan@HRPS.DEMON.NL>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         "J.W.Brier" <Jan@HRPS.DEMON.NL>
Subject:      Aux Battery: Life span of charged battery?
Comments: To: Vanagon list <Vanagon@vanagon.com>
Content-Type: text/plain; charset="iso-8859-1"

>But why do they call it a "Weekender if
>it won't keep your food and drinks cold for the weekend?


It's not that difficult.

Fridges use a lot of energy. No matter what, if you run a fridge off your main battery you will end up having no juice to start the car at some point in time.

So :

In order to avoid this situation you have to run your camping accesories from a different power source. That's where the extra (aux-) battery comes in. 

THE RULE 
========

The aux battery should only be used for the camping stuff, the main battery only for the car itself.

The explanation:

To achieve this you need two separate circuits isolated from each other by a relay. If you just connect two batteries in parallel it takes a little longer before they are both drained and will still need a jump start. The relay connects the batteries together as long as the engine is running so both batteries can get charged. With the engine off the fridge can only drain the aux battery but not the main one. This will give you much more relaxed wake-ups in the morning, knowing you can just turn the key and the car will go.

How long does it last?

For example, a typical car battery has a capacity of 50 Ah. That means 50 amperes for 1 hour. Or 5 amps for 10 hours. A fridge will draw approx 10 amps. So running continously it will drain the battery in approx 5 hours. It may run at say a 50% duty cycle giving you approx 10 hours before you need a jump start. You can use batteries with more capacity, but there is a limit. Stuffing all of your cabinets full of batteries may give you enough current for a whole week but then there would be very little 'payload' left. That may not be what you need either.

So in terms of fridge capacity - a weekender may not be more than an overnighter.

Hope this helps.

Jan Willem Briër (mr),
High Rise Professional Services, The Netherlands.
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E-mail: jan@hrps.demon.nl -- Tel. +31 (318) 548857  -- fax +31 (318) 548101
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