Sunday, Jan 09, 2011 at 22:39
Hi JFRCN,
Sorry for the diatribe above, 12V threads seem to bring out the worst in some people. As there are many ways to accomplish what you want, its hard to advise a cost effective solution, one could spend many $$$ to have a Rolls Royce system when a simple system would suffice.
Your current battery (assuming its in god condition) should be fine to run the Engels overnight and still be able to start in the morning. If you added a cheap low voltage cutout, it would shut the Engels off if the battery did start to get too low. But now you may have warm beer - a real tragedy.
So, the next question is how long do you want to run the Engels for without restarting the Rodeo? And how close to help are you in the event of a battery failure? If its just overnight and you are in Caravan parks each night, then go the cheap option IMHO. But if more than overnight Engel running or you are reletively remote, then a 2nd battery would be the best way to go IMHO.
It is possible to simply run the Rodeo every day for a few hours to top up a single battery, but this can be a pain. Besides, a battery can fail for many reasons, an Engel left running is only one of a multitude of things that may cause a flat battery. It is far from unheard of for a battery to drop a cell for no apparent reason.
So, my suggestion would be a simple low voltage cut-off if you are in Van Parks each night (can run the Engel on 240V too) and are not travelling remote. However, if wanting to stay put for more than overnight, or if travelling remote, then go the 2nd battery IMHO.
Now the next lot of fun starts. What type of battery (deep cycle, AGM, Calcium/calcium, normal wet cell etc..) and how to charge and isolate it. As you have already seen, there are many strong opionions on how to do this and most suggestions will likley work, it just depends on your requirments that will make one way more cost effective.
What I have done for my last 3 vehicles is to use a hybrid wet cell as the 2nd battery. It is a cross between a starting battery and a deep cycle, it will allow you to start the vehicle if the main battery dies on you, but also gives reasonable deep cycle capacity for normal use. Others may suggest AGM's or true deep cycle etc.. and they are not wrong, but all have plus and minuses.
An AGM is arguably the best battery type, but it is more sensitive to temperature and relatively pricey. True deep cycle will give better performance if only running an Engel, but if you ever want to run a winch or some other high current application (start the vehicle) then you will quickly kill a deep cycle battery. Choose the type that suits your needs and budget best, there is no one answer here.
Most dual battery installations go under the bonnet (hot!) as this is typically the easiest place to locate it. It also minimises the cable run, thus voltage drop. I run AGM's in my van but use hybrid wet cells under the bonnet. I figure I can charge my van battries under optimal conditions thus get the value out of the pricey AGM's. But under the bonnet, the high temperature is a battery killer so I go the cheaper hybrid wet cell as its more cost effective. There are many other technical reasons why too, but this reply is already way too long!.
Now all thats left is to charge/seperate the 2nd battery form the main battery. Again there are several ways to do this and their cost varies considerably. One is a "dumb" solenoid, it joins both batteries together when the vehicle is running and isolates them when the vehicle stops. Connect your Engel to the 2nd battery and it will never impact on your main battery.
The next step up is to use a voltage sensing solenoid, typically a redarc or some other brand. These are very similair to the above, but moniotr the main battery voltage to determine when to connect/disconect. The majority of 4WD 2nd battery systems use this type of system, its relatively cheap, relaible and proven in the field.
Another way is to use a DC-DC charger, it too can isolate the battery but has the advantage of being able to charge at the correct voltage. For under bonnet installations I reckon its overkill but if there is a long cable run (say the 2nd battery was in the rear tray), then it will help in charging the battery properly, especially if the cables have been undersized - but it adss considerable $$$.
So, I have now got probably you totally confused for what seemed to be such a simple question (this happens on many 12V threads!). The one thing I know is that I have successflully used a Redarc isloator with a hybrid wet cell battery under the bonnet on many, many vehicles very successfully over ~20 years. Sure there are other ways to do this, but IMHO its the most cost effective way for the majority of 4WDrivers and their typical usage patterns.
Cheers
Captain
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