Dual Shore Power Chargers?

[Birdman737]

Greetings all!

I am considering adding to my current 40A ProTech4 shore power charger a new 50A ProNautic 1250, and using both chargers on my 390Ah lead acid house bank when charging via generator power.

Why do I want more charging capacity? I have both a fridge and a freezer, and when you add their power consumption when running (6A + 6A) plus a few amps of house loads (maybe 3A), there's not much left to charge my batteries (40A - 6 - 6 - 3 = about 25A actually feeding the house bank). I've confirmed this with my battery monitor. When plugged in at the dock it doesn't matter since I've got all night. When anchoring out, though, replenishing even 75 or 100 Ah takes a while. I don't like disturbing the peace more than I have to even though my generator is pretty quiet.

My proposed two charger configuration could provide 90A of power, where effectively 75A would flow into a discharged house bank... tripling my charging rate. 75A is also still below the 20 or 25% max charge rate I could realistically expect from a 400Ah lead acid house bank.

So my question is, can I run two chargers into the same house bank at the same time? I expect both would run in "bulk" mode until the charger with the lowest preset voltage changed to "acceptance," at which time the other charger would gradually take over the remainder of the charging.

I realize it would be simpler to just have ONE big shore power charger, but that also costs lots more since my existing charger still works. I kinda like the possible redundancy this configuration could offer as well.

I think each charger would have its own switch on the AC panel, so I could easily control the charge rate of the batteries.

Am I crazy? Or is does this sound like a good idea? Thanks!

 

[Stu Jackson]

Sure you can, think of it like solar working when your alternator is running.

Thing is though, you could reduce your charging time by working between 50 and 85% of SOC and reduce your running time considerably. Putting that last 15-20% in takes a loooong time due to battery acceptance.

Do a search here on battery acceptance by Maine Sail and read away.

 

[Stu Jackson]

Save you the trouble of finding it:

http://forums.catalina.sailboatowners.com/showthread.php?p=674108&highlight=battery acceptance

 

[Rich Stidger]

Birdman,

I have had two chargers for years. I have my OE Guest 30A charger and I have a 80A Progressive Dynamics 4-stage charger. I run both from my genset to charge my 4 golf cart units.

The charge current starts at about 70A and drops quickly to 50A when the batteries are at 75% SOC.

 

[Birdman737]

Thanks guys! That's what I was hoping you'd say!

I realize the charge rate drops off a bunch over about 80% SOC, but I've found my main limitation when charging off the generator is capacity of the charger, not the battery's willingness to accept a higher rate. I actually verified this a few times by running the propulsion motor with the generator to see how many amps I could pump into my batteries near 50% SOC... and was still limited by charge capacity (50A alternator + 40A charger). I don't want to regularly charge my batteries with both engines, however.

I don't plan on attempting to "top off" the batteries' charge state with the generator... using shore power or a day of motoring every week or two fits in well with my current cruising style. My cruises typically don't last longer than two months either, so I'm limiting my exposure to "chronically undercharging" them as well.

 

[Benny17441]

I don't think we can isolate rate of acceptance as the sole factor in anticipating charger performance. In this case Birdman needs to replenish around 100 consumed amps while simultaneously continue to provide around 15 amps per hour. The charger(s) will be unable to discern between the acceptance rate of the batteries and the draw of the appliances and will respond providing more charge power for a longer period of time. The expectancy is that the charger(s) is/are able to supply the required 15 a/h in addition to the maximum acceptance charging rate. I do think the two chargers will work quite nicely, while keeping recharging time from extending. It also provides redundancy and perhaps extended battery usage between recharges.

 

[onecoolair]

Greetings all!

I am considering adding to my current 40A ProTech4 shore power charger a new 50A ProNautic 1250, and using both chargers on my 390Ah lead acid house bank when charging via generator power.

Why do I want more charging capacity? I have both a fridge and a freezer, and when you add their power consumption when running (6A + 6A) plus a few amps of house loads (maybe 3A), there's not much left to charge my batteries (40A - 6 - 6 - 3 = about 25A actually feeding the house bank). I've confirmed this with my battery monitor. When plugged in at the dock it doesn't matter since I've got all night. When anchoring out, though, replenishing even 75 or 100 Ah takes a while. I don't like disturbing the peace more than I have to even though my generator is pretty quiet.

My proposed two charger configuration could provide 90A of power, where effectively 75A would flow into a discharged house bank... tripling my charging rate. 75A is also still below the 20 or 25% max charge rate I could realistically expect from a 400Ah lead acid house bank.

So my question is, can I run two chargers into the same house bank at the same time? I expect both would run in "bulk" mode until the charger with the lowest preset voltage changed to "acceptance," at which time the other charger would gradually take over the remainder of the charging.

I realize it would be simpler to just have ONE big shore power charger, but that also costs lots more since my existing charger still works. I kinda like the possible redundancy this configuration could offer as well.

I think each charger would have its own switch on the AC panel, so I could easily control the charge rate of the batteries.

Am I crazy? Or is does this sound like a good idea? Thanks!

Okay I have read all the postings so far and not in disagreement. But here is another option. And what I have done. That is why not just give the batteries a break. I installed a continuous 12 volt power supply (120vac to 12vdc) that will run my freezer or just about anything else I need to have running on 12 volts while at the dock on shore power or out anchored and on generator. That way you may not need to spend the bucks for a extra charger.

 

[Benny17441]

A converter is a good idea to use with shorepower but at anchor it would require a constant running of the generator. I think one of Birdman's objectives is to cut down on the time he is running the generator.

 

[Stu Jackson]

To expand on Benny's thought: if the converter is being used for limited AC loads, AND the charger is not engaged, the skipper could be cutting off potential charging time if the generator is larger than the converter load.

 

[onecoolair]

That's the purpose of selector switch.

A converter is a good idea to use with shorepower but at anchor it would require a constant running of the generator. I think one of Birdman's objectives is to cut down on the time he is running the generator.

What?
That's the purpose of selector switch. #1 is 12v continuous power supply and #2 is House batteries.
Now if your freezer has an automatic switch over set up thats even better. Mine does not. So I went low tech .

 

[Maine Sail]

Am I crazy? Or is does this sound like a good idea? Thanks!

Not crazy at all. It will work fine

 

[Birdman737]

Thanks for your advice everyone... I'm planning on installing the second charger. The transformer / rectifier idea isn't really going to fit my needs.