20A vs. 40A charger?

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williamabernathy

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Hi, all. I am in the market to replace my Xantrex Truecharger2 40A, which seems to have bit the dust. From comments on BE, I'm not so taken with Xantrex and am looking at Charles or ProMariner.

My question here is what power rating I need: 20A or 40A (or somewhere in between)? I have two 8D house/starter batteries (for a pair of DD 6v53's), am usually on shore power and won't be on the hook for many nights (if that matters).

So what's the practical difference between a 20A and 40A charger?

Many thanks for comments (and brand comments are welcomed, too).

V/R
 
My 40a charger will only output 20a to each of two banks, so if you are considering a 20a charger, you may only see 10a per. I personally wouldn't go 20a, for the 10a per issue and for the time to charge. However I often overnight and can easily take a hundred amps out of my 300ah system in a couple of days. I want to recover a fast as reasonably possible. But that's me.
 
For my info, should the charger ever rate more per side than the A/C input per side or does it matted?
 
quote:
Originally posted by KiDa

For my info, should the charger ever rate more per side than the A/C input per side or does it matted?

Click to expand...


Outputting more then say 30a on a 120v/30a circuit is completely possible, as you're talking 14v vs 120v.

For ex: 120v at 30amps is 3600watts of power, while 14v at 30 amps is only 420 watts. So you could theoretically have a 14v 250amp charger with a 120v 30 amp supply. That's only theoretical, as there is of course loss in the conversion. - note that I'm not an engineer and just using my limited knowledge of power conversion for these numbers. But for sure total power is directly related to voltage AND amperage.

*If that's what you meant anyway...
 
A charger amp rating is for the the output side, at 12 or 24v. Nothing to do with the AC feed.

With 2 8Ds, I'd probably stick to a 30 or 40amp charger to make sure the batteries recharge fairly quickly especially if you run the generator only to recharge batteries while on the hook. At the dock, keep in mind the charger acts as a power supplies for your DC loads so if you use a lot of DC stuff incl. Halogen lights, unwatered lights, etc.. A larger charger will cope better.
 
40A it is, then (and tracking that the charger refreshes the house bank while on shore power, especially when 12v induction motors turn, such as head or shower sump, etc.).

Many thanks for all comments.

V/R
 
Bill, I'm one of the people on this forum that's had issues with Xantrex products. I have a 40-amp from them on the boat installed as a spare (my third warranty replacement), but I use a ProMariner "ProNautic" 40-amp charger as my main. It has been in service for about 3 years now and just does it's job. It also plays well with my 230-watt solar system. I'm charging a 315 amp-hour bank made up of 3 group 31 flooded batteries. I full agree with Pascal that for your 8D bank you should at least have 40 amps. I have heard nothing but good stuff about Charles, but my personal experience with ProMariner has been very good as well.
 
Kurt,
Thanks for the mention of ProMariner. I definitely had them in mind, along with Charles. Looks like a ProMariner 40A charger would be money well spent.

V/R
 
It depends on how you use your boat and what you have onboard using battery power such as a fridge. For example, if your boat is never away from the slip for more than a day or so, then a 20 ampere charger may work if you have enough batteries. If you spend days or weeks on a mooring or anchor, you need the largest charger you can reasonably purchase. You will want to replace as much charge as possible in the shortest time possible..........even if it requires monitoring the battery temperatures for charger shutdown.

And do not be fooled thinking a 40 ampere charger is going to charge at 40 amperes. The charging current is related to the fixed output voltage of the charger minus the battery voltage divided by the sum of the total circuit impedance which consists of battery source resistance, charger resistance and wiring resistance.

It will charge 40 amperes for a short time and as the battery terminal voltage increase, the charging current will decrease.

I have a fridge plus tv and other electronics depleting my battery bank. My charger is a 50 ampere Xantrex. When on anchor my generator would have to run all day to recharge the battery bank. For that reason I also installed 4 each 150 watt solar panels that pump out between 15-25 amperes depending on the sun condition. Heck, they are charging as much as 10-12 amperes at 8AM.

Foggy
 
Greetings: Had a 40 amp Xantrex for ten years with no difficulty. However made a change to a new Blue Seas 40A to look after three banks. The system manages the batteries. One bank generator, start, other banks two parallel deep cycle 31 series in each bank. Lived on the anchor for 7 weeks with genny running 3 hrs perday. No problems. Take a look at Blue Seas.
 
Running frig/freezer and maybe a fan for the heater at night some inefficient lights or microwave, I can put up 200-300 ah a day pretty easy. By day two I would be at 400-600ah. A 40amp charger would take more than a night to replace this. When I used to have a 65amp charger and an alternator that would only charge around 40 amps on a good day, we could actually almost go backwards if only spending 1 night in port. So depending upon one's situation, even only being out for one or two nights at a time could make life difficult if you were not going to be in port for more than a night. My charge rates now are around 100amps on the charger, 150ish on alternators and 200 on the DC Gen. Also, batteries like to stay charged, so its nice to be able to put charge back quickly when you can. So as you can see, if your going to be mostly a docked boat a 40 amp charger is more than fine. If you are out for more than a day or only at a dock for a night before leaving again, 40 amps can be considered quite puny.
 
It's all in how one manages power. We've anchored in the middle of nowhere for multiple days at a time. I've never had an issue keeping my 315ah house bank charged with a 40-amp charger. It is easier now that I have over 200 watts of solar, but even before that it wasn't a huge issue. We're running an ice maker (inverter), 12v water maker, freezer, and refrigerator. I can technically crank out 80 watts of charge as I have two 40-amp chargers, but I've never had to turn both on at the same time. My old engines (2 outboards) only put out about 9amps each. The new ones are closer to 16 amps each and even that is plenty to keep up with things.

As for batteries liking to be charged, you're darn right on that. I had a horrible experience with AGM batteries. I'm back to lead acid/flooded now. AGM batteries can't be equalized and thus must be brought back up to 100% each time they're discharged (hence, we only got one year out of them). Gel and LA batteries are fine with living between 50 and 80% charge since they can be equalized at the dock every so often to clean the plates off. I'd go with gel but outboards aren't set up to charge them correctly. I'm researching LiFePO4 batteries but I'm in no hurry since the 1 year old LA bank is holding up just fine.
 
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