Sunday, Dec 04, 2011 at 19:51
Hi Cobsy,
Frank has given some very good advice and I agree with it. I would suggest though that your vehicle aux
battery is likley stuffed if you have run it down to 6V on a few occassions. If that is the case, it doesn't matter what you are charging it with (dc-dc, alternator, 240v charger), you will never get the life out of it you want.
I would try charging the aux
battery on a good 240V multistage charger so you know its fully charged, then apply a known load like a spotlight (not a fridge, they cycle too much - or keep the lid open) and run the
battery down to 12V and measure the time it takes. 12v is approx 50% State of Charge (SoC) and thus you can work out just what capacity your
battery now has.
If you have a N70Z
battery, it will likley have a 75a/hr rating, or in that order of magnitude. If you use a 100W spottie as the load, that uses approx 8a/hr so it should take aprox 4.5 hours to get down to 12V.
I am guessing that it will take a lot less time to get down to 12V and thus the nominal a/hr rating of your
battery is way down due to running it down to 6V occasionally. If that is the case, I suggest you replace the
battery and in future try to minimise the time it is below 12V and definetly try and avoid lower than 11.5V as you will impact
battery life.
Now, a dc-dc charger for the camper is a must IMHO for the new cruisers due to voltage loss over the distance. However, I do believe that a dc-dc charger for the vehicle aux
battery will not give the same benefits - provided you use big cables between the main and aux
battery. There is certainly no harm using a dc-dc charger for the aux
battery, but the cost benefit is not the same. I have found in my 200 that the aux
battery remains fully charged and have not required a dc-dc charger.
The Ctek 250s is a good dc-dc charger, but the MPPT solar controller has a few limitations. It cannot run panels smaller than 80W in low light conditions and some users have reported troubles with even 160W panels in very low light. For this reason I went with the Redarc bcdc1240 charger in my camper and have found no issues with it in low light conditions - bit I do have 160W panels. I spoke to Redarc before buying my bcdc and they gave some good technical reasons why their MPPT controller can handle lower rated panels. If not running solar, no problem with the Ctek but if buying it for the MPPT capabilities then please be aware of its limitations.
Finally, I think that expecting 4-5 days from a 75 a/hr
battery (assumption here!) is too much if you want long
battery life. Even at a setting of 1, the Engels would draw over 1 amp and likley closer to 2 amps per hour (I have 2 x 40L Engels plus an 82L Evakool and have measure power draw over different conditions). Lets just say 1.5amps for the Engels and thats 36 a/hr for a 24 hour period. And thats about the max you would want to run your
battery down to (50% SoC) if you want long
battery life. Sounds like you may need the solar sooner than you think!
Cheers
Captain
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