Additional 220V->12V battery charger

[SVI]

I am considering buying the catamaran. The target boat is equipped with 9kw Onan 220V generator, 800ah service gel batteries (recently renewed) and 60A 220V -> 12V battery charger.

It looks to me it is not very efficent to use 9kw generator to charge batteries with just 60A (720W) charger (will take 6 hours to charge 50%). 800ah can take up to 180A charging current - can I add 2 more chargers and charge in 2 hours? how do I connect them? same model, or not necessary?

Thanks.

PS or I just buy a large 3-6kw inverter (will need it anyway) with charging? And use 60A charger as a spare.

[smac999]

if you don't have a charger / inverter I would get one of those. it will not be much more money as a good 100a 12v charger anyways. turn them both on at once. for faster charging.

do gels only take under 25%? agms take 40%

[SVI]

Can I plug in 2-3 chargers in parallel to the batteries? How are they measure voltage then?

[Dockhead]

Originally Posted by SVI

I am considering buying the catamaran. The target boat is equipped with 9kw Onan 220V generator, 800ah service gel batteries (recently renewed) and 60A 220V -> 12V battery charger.

It looks to me it is not very efficent to use 9kw generator to charge batteries with just 60A (720W) charger (will take 6 hours to charge 50%). 800ah can take up to 180A charging current - can I add 2 more chargers and charge in 2 hours? how do I connect them? same model, or not necessary?

Thanks.

PS or I just buy a large 3-6kw inverter (will need it anyway) with charging? And use 60A charger as a spare.

There has been a lot of discussion about this recently -- have a look in the archives, as I doubt if all the experts on here will rewrite everything they wrote in some recent threads.

Charging lead-acid batteries is complicated, and there are some conflicts of opinion about how long it takes to do properly, how much current they can take, etc. It would reward you to read the various opinions and make up your own mind.

The main thing you need to know is that lead-acid batts won't accept full charging current throughout the cycle. It takes much, much longer than just dividing amps of charger capacity by amp/hours of batts, and is generally not worthwhile to take beyond 80% with a generator. Although you will damage the batts if you don't take them from 80% to 100% regularly. Read the discussion.

My own short answer to your question is you should buy one charger (preferaly charger/inverter) with the right capacity; leave the existing one as a spare. I would not go over 20% of battery capacity, myself, as you can't practically use it, really, and when you do, it's not really good for the batts to charge them that intensively. 160 amps or so would be fine, in my opinion.

My own battery bank is similar to yours -- 420 amp/hours at 24volts, like 840 amps at 12v. I have a Victron 70 amp charger (like 140 amps at 12v) with nominally 3000 watt inverter built in.

I have a 6.5kW genset. I have never felt the need for more charging capacity -- my charger puts out its full output only for a while anyway during the charging cycle.

You will want to avoid running your genset just to do a single task like charge batts. It's good to charge yours batts at times when you have other uses for the AC power -- even heating water. Washing clothes (if you have a washer/dryer), cooking (if you have any electrical equipment in your galley), etc.

Good luck and let us know what you end up doing.

[djmarchand]

Dockhead is correct. Go with the large inverter/charger with 150 amps of charging capacity. And add a battery monitor. Let the batteries drop to 50% before starting the genset and stop when they reach 80-85%

But you need to charge them to 100% at least every week or so, otherwise they deteriorate. A solar panel is good for this.

David

[omgitsgela]

Depends how the batteries are connected. If they are all in parallel (12 volt system), then power will (mostly) distribute across the batteries, however strange readings can occur on the charger during the finalization cycle if one of the batteries isn't in good health.

The best way to do this is to network a series of inter-disconnect switches between each battery or battery group, then wire in your chargers. Say, for example, having DPDT switch that goes between regular setup and charger lines, and run one charger per battery (or one per two, if you are going to ignore the battery health warning)

One thing's for sure: an energy-depleted battery will NOT charge in two hours. Think more like 10 hours under ideal conditions for a full charge from zero. This limitation is due to chemistry.

Lead acid's want to be at full charge as much as possible. When you start draining and going back to 80% over and over, they sulfate and develop deteriorations in the lead. The danger in running chargers ganged on multiple batteries is that if one charges more than another, you'll boil off electrolyte. Make sure specific gravity and fluid levels are matched for sets of batteries, as well as capacity, and hell, even when you purchase them. I run two 12v 85 ah in parallel on one charger, but only because I bought them at the same time.

Charging Information For Lead Acid Batteries

You're absolutely right that a 9kw generator is overkill. Change your idle speed down maybe?

[SVI]

What are the recommended brands for an inverter/charge combi?
I would need a 3kw one - plan to run washer and microwave from the inverter.
Will add some solar on the roof as well.

[omgitsgela]

Originally Posted by SVI

What are the recommended brands for an inverter/charge combi?
I would need a 3kw one - plan to run washer and microwave from the inverter.
Will add some solar on the roof as well.

Oh, I have no idea! :P

The stuff I came up with is via hacks and third party equipment. I don't buy any fancy nautical this or cruisers that nonsense overpriced stuff. Sorry!

[SVI]

Originally Posted by omgitsgela

Oh, I have no idea! :P

The stuff I came up with is via hacks and third party equipment. I don't buy any fancy nautical this or cruisers that nonsense overpriced stuff. Sorry!

I do not mind using third party equipment - please kindly provide the details.

Otherwise, what's the point of replying if you have "no idea"

[Dockhead]

Originally Posted by SVI

What are the recommended brands for an inverter/charge combi?
I would need a 3kw one - plan to run washer and microwave from the inverter.
Will add some solar on the roof as well.

Solar is very good for your batteries -- highly recommended.

The premium charger/inverter brands are Victron and Mastervolt, both made in the Netherlands. I have all Victron equipment on my boat and have had a lot of failures. It is beautiful and fantastic when it works, but wouldn't really recommend it. I've had a lot of problems with it. The warranty service is fine, but that's little comfort when the installation costs more than the unit itself.

I have no idea about Mastervolt; never used it. It's original equipment on Oyster yachts. It's expensive -- like Victron.

A budget brand made in the UK is Sterling -- inexpensive, and I have heard great things about it from users and professional electricians. Maybe worth a try.

Newmar makes a high quality charger, but I don't know if they make a charger/inverter.

Xantrex is notoriously unreliable from what I hear -- but I can't imagine that it is less reliable than the supposedly premium Victron stuff.


Be very careful about sizing your inverter. The practical working load is far less than what's on the box, and even less at higher temperatures. Mine is nominally 3000 watts (actually, if you read the fine print, 3000va, which is not the same thing), but a practical working load is not really more than 2000 watts. Of course, with an 800 amp/hour bank, you won't want to be using loads of 2000 watts for long periods of time anyway.

I use a full sized microwave fine with my battery bank and inverter. Also Nespresso machine, toaster, power tools, and all kinds of other things on board. I could not run a load of laundry off batteries, however. I have done it when the main engine was running, but since my charger/inverter blew up last fall for no apparent reason, leading to a torturous and horrendously time-consuming removal and replacement for warranty service, I don't think I'll be pushing it that hard any more.

[Dockhead]

Originally Posted by omgitsgela

You're absolutely right that a 9kw generator is overkill. Change your idle speed down maybe?

Huh?

[omgitsgela]

Well, I did post useful information, including links to how lead acid batteries work BEFORE that post, but the forum decided to be dumb and ask for moderator approval before posting. Maybe it'll still go through

As I wrote, I have two 85 Ah batteries hooked up in parallel to offer twice the capacity. I keep them ganged together, but only because they were both bought together and will share equal wear and loads together as they age. I wouldn't dare try this with batteries of differing age per bank due to specific gravity differences that would affect charge duration. If you apply 14 volts for charging to an already full battery in the bank, bad juju happens.

I use a smart 25 amp black and decker charger for continuous draw on a 120 volt input system. It's easy, automatic, and doesn't require any button pushing to operate. For the sake of the forum, I'm not going to post the link should the gods of the links reign terror on me.

If you do have batteries of different condtions, capacities, etc together, consider rigging up a battery charge disconnect panel with DPDT switches to cut out the batteries from the main circuit and put them into smaller charging banks for parallel charging. Those little 25 amp black and decker chargers are small enough that you could definitely stack them up on different banks, but don't expect any less than 10 hours charge time if you are going from depleted all the way to full. That last 20% is super important for the health of the battery.

Another thing -- running loads off a battery charger IS possible, but ill advised. Depending on what kind of voltage drop occurs in your system as devices are turned on, the charger might think the batteries are dead instead of just running your devices and apply a 14 volt current to already charged batteries. In theory, the electricity should only flow to the devices being used, but I don't know what the resistance is of a lead acid battery across its terminals when full.

[SVI]

Dockhead,
Thanks, really helpfull.
Will change the system design for a small loads from the inverter / large loads (washing/watermaking) from the generator directly.
Will probably separate charging and inverting: will put 2-3 60A chargers and one 3000W inverter.

[goboatingnow]

Originally Posted by SVI

Can I plug in 2-3 chargers in parallel to the batteries? How are they measure voltage then?

yes you can , both will contribute during bulk phase, one will most likely contribute all the current during the absorption phase


dave

[SVI]

Actually, I am thinking to try this Chinese inverter with 100A charger. They all are made in China anyway, so why to pay double-triple?
May want to put a smoke detector next to it and fuse it well )