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bobct

Advanced Contributor
I have an old ferro 30a, promariner charger that is original to the boat ('88). I just bought a hardly used Charles unit from a guy on craigslist for $80 but it's a 20 amp. Both are 3 bank chargers and I only have lead acid batteries.

The Charles is a few years newer but looks brand new, the SS case doesn't hurt compared to my old rusty one. My questions is, how much longer will it take to charge the batteries at 20a vs 30a assuming an equal state of discharge? I have no idea how long it takes now with the 30amp.

I guess I really don't care in the slip but might when running the generator on the hook. Again, no point of reference whether the difference is mins or hours.

thanks!
 
Hi Bob:


I have an 80's vintage ferroresonant 60 amp unit that is barely adequate for charging on the hook. It just never seems to get the batteries completely topped off (6 group 27's) no matter how long it runs.

We just purchased another boat and it has a 40 AMP charger. I consider this inadequate for the task of charging the 4 D batteries and one group 27 generator starting battery that are aboard. I'm going to upgrade this unit to a 100 charger/inverter. Probably not right away, but quite possibly before the year is out.

You can calculate AMP hour storage capacity and charging rates, etc. If the genset has to run for more than two hours so that the charger can deliver a full charge, than the charger isn't up to the task. Peace and quiet is one of the best things about being out on the water. So how long do you want to run yours everyday?

Best wishes,

Tom
 
Tom,

I only have 3 batteries, Two 6v in series dedicated to a wet bar fridge and a start battery for each engine which also serve the respective side of the boat. I'm going to use a Honda 2000 as needed. I haven't actually done it yet so I'm not sure how long I'll need. An hour a day would be ok with me as you can barely hear the Hondas. If it's going to be a multi-hour event than maybe not so great.

In reality, my fridge bank will run for 2-3 days w/o a charge so I only need the generator on demand (micro, stove) and to top off my start batteries which have the house drain.

I think the total output from the Honda is 13 amps so I'm not sure if it will be any "slower" charging with a 20a vs 30a charger. Or would it be faster with a 60a charger? I don't really care how long the charge takes in the slip.

Bob
 
My questions is, how much longer will it take to charge the batteries at 20a vs 30a assuming an equal state of discharge?
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33 percent longer, assuming constant rate of charge. I know that sounds too simplistic but it is Ohm's Law.

I guess I really don't care in the slip but might when running the generator on the hook. Again, no point of reference whether the difference is mins or hours.
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You can figure it out pretty easily. Tally up your total daily amp-hours draw from your batteries (for example you burn a 20 watt bulb for four hours; that's roughly 2 amps times four hours is 8 amp hours) Batteries are measured in amp hours (ah) and/or reserve capacity. Therefore a 200 amp hour battery can sustain a 20 amp draw for ten hours before is is effectively dead. For safety's sake you never want to go below 50% of that and really 30% is a better number because constant deep discharges will shorten battery life. Anyway, once you know how much juice you have in the "bank" and how much you need to take out every day (with that 30% discharge safety margin figured in) then you can calculate how long it will take to recharge the battery at a given amperage. So, if you have a 200 ah battery, you never want to take out more than about 60 amp hours between charge ups. Doubling your battery bank will give you a lot more reserve and will give you longer battery life because they are being drawn down less by having the load split.

Modern smart battery chargers recharge in stepped increments or phases. This helps get big juice back in quickly and tapers it off as the battery comes back closer to a full charge. These are also programmed for flooded, gel, and AGM type batteries.

One thing that makes a huge difference in power management is switching all your lighting to LED. You can go from 10-15 amps draw to almost zero, which is significant in terms of running the genny and the engines to recharge the batteries. They'd pay for themselves pretty quickly with gas prices the way they are.
 
a start battery for each engine which also serve the respective side of the boat.
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I hate to sound like a tool, but this is just wrong. I'm sure you didn't set it up this way yourself but whoever did wasn't thinking straight. You really aught to take the house loads off the start battery and keep those just for engine starting. Running down your start batteries is a safety issue unless you always boat near shore or within cell phone range so someone can come get you if the start batteries go flat.
I'd put the house loads on a dedicated house bank and connect the alternator and generator output to that with a VSR to bleed off charge current to the start batteries.
 
bob:

for a fixed discharge, it will take about 50% longer...not ohm's law but energy transfer. 30 amps for an hour yields 30 A*hr. with a 20A source, it will take ~ 90 minutes.
 
What's your hurry? The batteries will get charged up eventually, and slower charging is better for them. I use a trickle charger on one of mjne and it's always ready to go.

Jeff
 
I'm running out of time!!!

Actually at the slip, I don't care. It was a generator re-charge I was really questioning w/o having any baseline for how long it takes now on shorepower. Thanks guys, that helps.

o2batsea.... this is my setup from the factory and no battery switches either. I do have a factory "emergency start" switch/solenoid which will bridge the two batts together for starting. Going through the LED upgrades now.

Bob
 
o2batsea.... this is my setup from the factory and no battery switches either.
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If boats had to adhere to federal safety standards the way cars do, then the lawyers would be all over that setup. Good news is that to remedy this requires very little in the way of wiring and rerouting the loads.
 
The batteries will get charged up eventually, and slower charging is better for them.
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The battery manufacturer should be able to tell you the max absorption rate for a particular battery. When recharging, the battery should be charged at this rate (varies by chemistry, temperature and state of charge) until it is up to a full charge and then switch to a float charge level. Float charge won't recharge the battery, but will maintain its state of charge. Trickle chargers like a Battery Tender cannot recharge a battery very fast. Days not hours. Multi step or "smart" chargers monitor the state of the battery and correct the voltage accordingly. They'll recharge much faster than a constant current type charger. In addition they can also supply equalization charge for batteries that are sulfated or "dead" which may bring them back into service...but that's really an emergency type of thing as it will gas the battery fiercely.

If charging from the engine alternators, use of a "smart" alternator regulator will do the same thing when away from shore power.
 
What ever you do, if you go with a higher output charger, ensure that your current wiring will handle the higher output or replace accordingly. Keep in mind that a charger's output rating is devided into it's output banks as required. A 60 amp charger for example will not supply 60 amps to all three banks at the same time...it's 60 amps total. Some multi bank chargers have a set max per bank (ie 40 amp: bank 1=10amp, bank 2=10amp, bank 3=20amp) while others can supply full rating to any given bank. You must keep this in mind and sellect the appropriate charger for the size of batteries you are running. If one bank runs very low, you want to make sure that it will handle a 100 amp dump from a 100 amp charger if that's what you get. Again, you must take this into consideration when determining cable size.
 
after some back and forth and actually trying to install the Charles unit, I ordered a Promariner Pronautic charger the other day.
Even though I only have lead acid batteries now, that might change at some point.

If anyone is looking for a ferro 20a, 3 bank Charles unit shoot me an email. It's a stainless case and looks beautiful.

Bob
 
I know the ferros have a bad rap for cooking batteries. They can't help it, it's the physics involved in the design that make them that way. Having said that, they are much more robust than the fully electronic smart units that are the standard today. I have heard good things about some encouraging strides they're making in newly designed ferro units that incorporate new age electronics to overcome the ferro's inherent physical limitations. If they are successful, these will make very good chargers.
 
I have to say, in spite of all that I heard... the old Promariner ferro unit never did any damage to my batteries. It's been plugged in basically full time for the last three years on the same batteries and the water level never dropped. I've read the same thing that they "cook" the batteries but I'm just not seeing it from a 23 YO charger.
 
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