battery charger?

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nazar

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Mar 1, 2021
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augusta western australia
hi, new to forum, live in australia. new to caravaning so been doing a lot of research. outings probably 3 times a year for a couple of weeks.

for a battery charger decided on CTEK mxs10 - but i am unsure as they say "10 percent of amps"
currently i have an 85amp CCA deep cycle (yes, i know it is bad)
will upgrade to 2x AMP 110 or 135 deep cycle (which makes 220 or 265)

so thinking the next one up of CTEK, problem is projecta website is really easy to navigate, but the CTEK website is pretty bad for a newby.

am i on the right track? and what is the next model up from the mxs10? - want as easy as possible smart charger.

any help appreciated :)
 

cerd

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MN
Very rarely do I have a problem with charging batteries unless they are lithium. In that circumstance, slower is better. The one time it was an issue was because the battery developed a memory somehow. It wasn't accepting the trickle charger, but it would charge on the alternator. The guy at Napa hooked it to a higher output charger and it started working again. But that was once out of probably 50 batteries in my lifetime. As the guy explained it, the battery was used to a higher charging current and wasn't accustomed to lower currents. In general, I don't go by ratio of the capacity, but the rate of draw and I haven't had an issue. My converter puts out 45A, so when I need to charge the batts, I usually just plug in the rig in the driveway for a day or two.
 

Mark_K5LXP

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Probably the first thing to consider is if this charger is to restore a charge quickly, or just maintain the batteries.

When camping, you often want to recover depleted batteries as fast as practical to take advantage of limited generator run time or AC power availability. Contrasted to when the camper is sitting at home or in storage and you just need a slow or maintenance charge. This distinction is made at the CTEK site -

"The MXS 10 is a fully automatic 8-step charger that delivers 10A to 12V batteries from 20-200Ah and is also suitable for maintenance charging up to 300Ah."

So it's saying it can fully charge batteries up to 200Ah but if it's just maintaining a charge, it can accommodate a 300Ah battery. But charging 200Ah of battery with a 10A charger would take literally a full day or maybe a little more, so that's the tradeoff you make vs a larger charger.

So the question to answer first is how quickly you need to restore a charge and pick your charger accordingly. Most battery data sheets recommend to not exceed 1/10 the battery's capacity for a charge rate but most folks go with up to 1/5 in the interest of recovery time.

Mark B.
Albuquerque, NM
 

Gary RV_Wizard

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I didn't find "10 percent of amps" on the Ctek site, but maybe there is a different site/page for Australia (I viewed a UK-based site). However, it's a 10A (max output) charger, so an educated guess won't be far off. The charger will deliver at most 10A if the battery(s) is somewhat depleted in charge, but taper off to as little as 2-3A when the battery reaches the 80%-90% charge level.

I'm also unclear about your battery terminology, but if 85A means the battery has an 85 amp-hour (AH) capacity (measured with the industry standard 20 hour rate test), then we can estimate that the charger will require 5-6 hours to restore the battery from 50% charge to 100% charge, i.e. replace 40-43 AH. That's around 3.0 hours at 10A to bring it up to about 90% charge and another 2-3 hours at lesser rates to reach 100%. A bigger charger will get to 85%-90% sooner, but the last 10% will always be slow.

Since you plan to get more & larger batteries, I recommend a larger charger. At least 20A capability.
 

IBTripping

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I see this is your first post. Welcome to the Forum. As you can see from the above responses, the Forum has a lot of helpful experts.
 

nazar

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Mar 1, 2021
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augusta western australia
thanks guys, sorry for the confusion - this is all new to me so been doing lots of research,
currently have a marine deep cycle 85amps that you can crank an engine with (CCA - constant crank amps) - these batteries have a different chemistry and are not as good as the dedicated deep cycles.
so am thinking of upgrading to AGM and when i upgrade, the charger may not be enough..
10% is what is recommended on the forums, not the ctek site

i think mark is right, i should get a faster charger.. can't work out the ctek site - what is the next ctek above 10??????
 

Gary RV_Wizard

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currently have a marine deep cycle 85amps that you can crank an engine with (CCA - constant crank amps) - these batteries have a different chemistry and are not as good as the dedicated deep cycles.
I think you have misunderstood what you read or what you have. 85 amps is about enough CCA to crank a small lawnmower and maybe a small motorcycle. A typical 12v marine deep cycle would be more like 450-500 CCA.

Deep cycle battery capacity is measured by either Amp-Hours (AH) or Reserve Capacity (RC). Learn more about those terms at https://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html

Further, AGM batteries have reduced maintenance requirements vs flooded type batteries but aren't necessarily an upgrade in capacity, whether measured in CCA, MCA, AH or RC. Those values are pretty much determined by the physical size and the amount of lead plate inside.

I've written a brief tech article that tries to simplify battery choices for RVers. A copy is attached. If you would like the longer, more in-depth version, please contact me via private conversation.
 

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Gary RV_Wizard

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Back to your charger size question, a common rule of thumb would be that the peak charging amps should be 1/5 to 1/10 of the battery bank capacity in amp-hours (AH). The combined capacity is often designated as "C" in battery discussions. Using that as a guide, if you had two 12v batteries of 100AH each (a "C" of 200 AH combined), a charger capable of 20A would be minimum (C/10) and a 40A charger (C/5) would be more desirable.

There is no magic number - the more charging amps available, the sooner the battery will reach full charge (within limits, anyway). A 1 amp charger will get the job done eventually, but a 50 amp charger will do it faster, However, there is a practical limit of charge rate for a given size of battery, so a 200 amp charger may not always be much faster than the 50 amp.
 
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