Scoping out chargers...

[ssullivan]

I wanted to see if anyone had a line into some really inexpensive bulk battery chargers in the 200amp range (or two 100 amps I can hook up to make 200amps).

Remember... I have alternating current running an hour or two each day, and I will be out at anchor constantly... so I will be only charging up through the bulk phase and equalizing once a week or two.

I am considering building my own, after realizing that it's much cheaper to build your own refrigeration and/or watermaker. If a simple bulk charger is way overpriced, I'll gladly get out my soldering iron and an electronics parts catalog.

If you are still considering a large inverter, many of the inverters come with built in chargers in that range.

[CaptainK]

You could always have a treadmill. And have a dog chasing a cat all day long that'll work.

Or you could pick up some horny teenagers. And have the male teenager running on the treadmill, chasing after a nude lady? That'll keep the charge constant!!

[coot]

I have two of the IOTA 75 amp battery chargers. I bought them from http://www.jackrabbitmarine.com

Each is wired to on a separate 20 A ac power circuit. The absolute maximum current draw in the specs is 18 A at the low end of the AC input voltage range. My generator is rated for 35 amps, so in practice I have power to run both of them and a few small AC loads.

I use them to charge 840 AH of AGM batteries with my generator. I usually discharge the batteries to the low 700's and then recharge from the generator for about 2 hours. I shut off the generator then because that is the point of diminishing returns. It takes about 4 to 4.5 hours to recharge to 100%, but I'm not going to run the generator for an hour to put 20 AH in.

These units are not "really cheap" at around $300 each, but these are well-built switching power supplies. They do not get very hot.

I guess you have some electrical engineering training, but even so I think it would be a lot of work do design and build something similar.

If you go that route, I highly recommend using several lower capacity chargers in parallel. I've been very happy with the ability to run just one of them at a time because I can shut off one when I want to run another high load AC device. I also like that I can run at half capacity in event of a failure.

[ssullivan]

Kai Nui once whispered in the wind:
If you are still considering a large inverter, many of the inverters come with built in chargers in that range.

Thanks, Kai Nui. Already saved big $$ over the standard inverter/charger scheme by using two smaller inverters. I never needed the power one of those huge units delivers, especially with a genset. I ended up opting for the inverter I already had (500 watts) and another 1.5KW inverter for my entertainment center and the very VERY occasional hair dryer. Neither is hooked up to the main AC supply, so it's easy to control/wire them. There is one outlet built into my "entertainment center" that runs off the 1.5KW inverter, and this can be used with an extension cord to vacum, run power tools, blender, etc... (short bursts of energy)

Total cost... $300?

Now I'm trying to find a charger to just dump a continuous current into my expanded battery bank. This will bring my batteries up through the bulk phase of charging, where the "point of diminishing returns" on running a genset is. I'll cycle my batteries through 80-90% charge, down to 50% charge on a normal day, then blast 'em every once in a while to avoid sulphation. (or charge them fully)

Great advice, Coot. I'll take a look at those. Sounds like we are just about in the same situation. I have a slightly smaller bank (600AH), but still will need something similar. I'm hoping to cut charge time down to under 2hrs. I have to do a little math to see what my projected charger amps need to be to acheive that.

[ssullivan]

What about the "el cheap-o" car chargers that come in 100AMP(starting current) models?

Can you leave the starting current on for extended periods of time? As in for an hour or two to bring a battery up through the bulk phase?

I had one in the past, but can't recall if you can leave it in "staring mode" and just let it rip or if it will heat up and catch fire or not. ha ha

[markpj23]

The IOTA units look good IMHO. Best of all they are frequently available on eBay direct from the manufacturer for much less than the best reseller prices I've found.

Unfortunately my quick eBay search this morning found no current listings.

[NoTies]

I'm not sure if things have changed since I was drinking large amounts of rum as a student but I was always told you shouldn't charge more than 15% of your battery capacity. Is this till true?

[ssullivan]

Thanks for the input, Pwederell. I know that c/10 (10% of your capacity) is the lowest practical bulk charging amperage. I thought I had read in Nigel Calder's book that the upper limit was around 25%?

Also, I did take a look at the Iota chargers. They are still 3 stage chargers. Here is a little thread drift, but this reminds me a lot of when I was shopping for a stereo amp that would play a stereo signal through a pair of speakers. I didn't want surround, I didn't want it to make coffee, and I didn't want a lot of crap they installed just to jack the prices up on a mediocre unit.

Same thing with these chargers. I just need a constant current charger to do bulk charging, and that's it. I already have a 50AMP charger that will handle absorbtion and float stages when I'm running the genset all day or connected to shore power (which will be very infrequently).

Does anyone make a 100AMP-200AMP constant-current DC power source that just dumps out 100-200AMPs at the bulk charge voltage?

It would seem to me that one might be able to find/build a constant-current rectifier circuit capable of high power (100 AMPs+). Can only seem to find expensive "smart" chargers loaded with features. These are great if you have all day to charge your batteries. I have 2 hours, max.

The percentage thing was discussed to death in another thread, so I won't go there, but the consensus seems to be 25% is OK.
Car chargers are battery cookers unless you go very high end, however, if you size it correctly, and only use it, as you said for a couple of hours to recharge the bank, and do not rely on the float mose, you should have no problems.
I do like the sound of the IOTA units. The price is within reason as well.
The big issue with marine chargers is that most people use them dockside, so they are providing most of the current for the 12 volt accessories, and on all the time. The batteries never cycle, and if the charger is not designed to be a constant power supply, it will fail prematurely. If the float function is what fails, it will take your batteries with it. This is not an issue with your application. With your use as needed set up, you can go cheap. You will still want to look at a charge that is suited for the type of batteries you have. If you have lead acid, anything will work, but if they are gels or agm, you will want to talk to someone who knows the specific charger before purchasing. Hopefully they will give it too you in writing that thier unit is safe for your application

[ssullivan]

Ha ha ha!! Yeah, they better get that in writing... lest they end up on here! (joking)

For any nay-sayers, you can all see that I dish the bad with the good. Check out my reccomendation for Independing Boat Haulers in another thread. See what good customer service does?

Anyway, I just learned something from you, Kai. I had no idea standard 3 stage chargers shouldn't be used as a DC power source dockside. I am currently doing just that with my "original equipment" 50amp, 3 stage charger. Hope it makes it until May, when I leave the dock for good. Any better way to supply dockside power for months at a time? Are you doing something differently with your high-end charger/inverter?

Very curious!

PS: I'm probably sticking with lead/acid. Not 100% sure yet, but most likely. I have a nifty spreadsheet someone made up that analyzes your electrical system to death. You enter loads, gensets, cost of fuel, solar, whatever you have on the boat (there are spaces to fill all this in) and then it calculates operating costs bases on a zillion factors.

Hey, is there a way I can put this file up for all to have access to on this board?? It's very helpful.

[CaptainK]

I could send you my email address in a PM, Sean. Would ya do that for little ole me?

Sean, good with the bad right?
I am familiar with that form. I used to have one on my computer. It is a great tool when planning a system. I strongly recommend downloading one (there are lots available online), and filling it out before making any changes to a power system on the boat.
As for the charger as a power supply, some do better than others. I had the West Marine cheapo, and it failed. I was told that this is the reason. I purchased a Guest that is specifically rated for this type of service. OTOH, I used to use small automotive chargers for my ham radios with no problem.

[CaptainK]

Hey Kai!!

Could you email me that downloadable planning system, that you and Sean were talking about?

K, I no longer have the worksheet on my computer, and I am having problems downloading off the internet. Computer issues that I do not want to get into. Too drawn out.
Simple list:list all appliances that require electricity
list their voltage (12 or 110)
list their maximum draw
seperate electric motors and multiply draw by 3 for start up
estimate hours used per day including 30 second at 3x rating for each start up of motors
This will give you your daily usage in amp/hours.
multiply the amp hours of all the 12 volt, and the amp hours of all the 110 volt items times the voltage. This will give you watt hours. This will give you usage. Your system should be based on this final number. Ideal battery capacity should reflect discharge of no more than 20% of total battery capacity. While batteries can handle a deeper discharge, this is a safe average.
sample:TV 5amps @ 12v=60watts x 2 hours=120watts
+refer 10amps @ 110v=1100watts x 4 hours=4400watts
daily usage is 4520watt/hours
To add another factor, the ac components wil be run through an inverter. if the efficiency of the inverter is 90%, multiply the ac usage by 1.1=4840
this leaves a total of 4960 watt hours per day. divide this by 12 volts=413.33amp/hours per day. An ideal system, that will require recharge once per day will be 413.33amp/hours x 5=2066.65 amp/hours. This would be a huge system, and the draw shown the above appliances does not relect reality, but is just a sample number. I will not get into recharging, as that is a big subject, with lots of variables. Also keep in mind that this is highly simplified, and you can get away with running the batteries down 40%. THese are optimum numbers. Based on the formulas here, you should be able to build a spread sheet to design a system.