12v system

Submitted: Saturday, Aug 29, 2009 at 20:15

ThreadID: 71872 Views:2842 Replies:2 FollowUps:3

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Battery Power

In this article we explain why you might need an additional power source independent of the starting battery installed into your vehicle and we look in detail at types of batteries,

Member - Tony Z (NSW)

Its been asked before BUT - I have had a 80AH deep cycl Aux batt. fitted under the bonnet with an isolater and a 50amp Anderson plug to the rear of the vehicle. the question is, I would like to fit a 100AH deep cycle batt. in the camper trailer and charge it through the Anderson plug, this batt will not be running any appliance while travelling only when stopped ( some nights bush camps some van parks 240v) ie- fridge & 1light
Will the batt be damaged if left connected to anderson plug all day while driving if it is already at full charge
Thanks for all replies in advance

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Reply By: Robin Miller - Saturday, Aug 29, 2009 at 21:08

Saturday, Aug 29, 2009 at 21:08

It will be Ok Tony

AnswerID: 381008

Reply By:- Thursday, Sep 03, 2009 at 10:12

Thursday, Sep 03, 2009 at 10:12

Tony, your battery in the trailer will have a shortened life if the charge voltage is not regulated to the temperature compensated float voltage if cruising for extended periods.
E.g. if your alternator outputs 14V, and your battery sits in a moderately hot environment of say 35 degrees, you'll be overcharging by 0.75V.
Even in temperate environments of around 25 degrees, you'll still be overcharging by 0.5V. Not good.
The recommendation I give my customers is to put a diode in series with the charge wire to your second battery in the back.
If you want your second battery to assist with cranking, bypass the diode with a switch (or jumper lead) which you only close while cranking.
This setup has the advantage that you can fully cycle charge to 100% (14.7V?) your second battery while cruising along by means of your battery charger connected to an inverter which runs off the main battery. The diode in the circuit isolates the elevated charge voltage from the lower alternator voltage.

Best of luck, mr.batteryvalue

AnswerID: 381740

Follow Up By: Redback - Thursday, Sep 03, 2009 at 13:17

Thursday, Sep 03, 2009 at 13:17

Rubbish, the cars alternator will regulate the charge rate.

FollowupID: 649338

Follow Up By:- Thursday, Sep 03, 2009 at 13:53

Thursday, Sep 03, 2009 at 13:53

@ Redback,

the following may not be part of your knowledge yet:
lead acid batteries want to be float charged at a temperature dependent voltage of around 13.6V (@20 to 25 degrees).
Car alternators are designed to output around 14V for a number of reasons hence are overcharging any fully charged lead acid battery, especially under elevated temperatures.

If you want to float charge a deep cycle battery in the back of the car, by using the 'raw' alternator output you'll inevitably shorten the life of this battery.

Anyone seen a temperature compensated alternator output voltage of 13.6V in a car/truck/boat?
Probably not, because you're going to undercharge any battery if you don't bring it up to at least 14.4V after a deep discharge.
This's what it's all about the single stage versus multi stage battery charging....

greetings, mr.batteryvalue

FollowupID: 649344