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Old 29-11-2009, 05:09   #31
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Originally Posted by R_C View Post
Not Sure,

I disagree. While I'm only using 20 to 25% of the Ah capacity of my bank in 24 hours, in practice I may be discharging the bank to about 65% state of charge many days. That's because I don't attempt to fully charge while at anchor.

- Rick
Rick, I see that you say you go down to 65% so you are probably using around 150a per day just like me.
I put this back in around 1 hour.
I think that with a 90 amp charger you will need just under 2 hrs. Remember that you do not get all 90 amps as you are probably using 10amps dc for other stuff at the time of charging so you only get 80 amps.
John
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Old 29-11-2009, 10:40   #32
R_C
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Originally Posted by john Fussell View Post
Rick, I see that you say you go down to 65% so you are probably using around 150a per day just like me.
I put this back in around 1 hour.
I think that with a 90 amp charger you will need just under 2 hrs. Remember that you do not get all 90 amps as you are probably using 10amps dc for other stuff at the time of charging so you only get 80 amps.
John
John,

When charging we have very little DC load. Our refrigerator automatically switches to AC from the genset and we deliberately switch our two laptops to AC to maximize charge current.

150Ah per day is my calculated maximum. We typically use closer to 100Ah in a day. I know I could use an even bigger charger or even run both the new 90A and existing 40A charger simultaneously during bulk charging. With my current 40A charger it takes over 2.5 hours to restore 100Ah during the bulk phase. For about $400 for the Iota 90A charger I should be able to cut that time in half.

- Rick
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Old 29-11-2009, 11:03   #33
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Hi Rick,
Yes thats what I do, run both chargers at the same time. Then your generator time comes down to under an hour each day which is what I have as well.

Under an hour is fine, but more than 2 is a pain.
I often wonder why generator boats dont have their battery chargers sized right to minimize the run times on the generator.
John
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Old 29-11-2009, 15:49   #34
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John,

When we bought our boat it had a very old 30A charger and a 400Ah house bank. I mistakenly (I swear I read this in a Nigel Calder book) believed the maximum charge current for AGMs was 10% of the Ah capacity of the bank or 40A for a 400Ah bank. I've since learned that is not true. Although the technical manual for my AGMs does not list the maximum charge current it does include a charging current vs. time graph which tops out at 80A on a 200Ah 4D battery. 80A is 40% of 200 so if I extrapolate, I should be able to apply 240A to my 600Ah bank.

Now I'm thinking I should just run both chargers simultaneously during bulk charging for up to 130A. Have you had any problems running both your chargers? To occasionally get a full charge, do you turn one off after the bulk phase and let the other charger continue?

- Rick
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Old 29-11-2009, 23:16   #35
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Hi Rick,

No I have no problem running both chargers. They both run in bulk mode until reaching 28.5v, then they go into absorbtion mode and reduce the amps gradually until float mode, once the amps have dropped off to around 10a I think.
My engine alternator is 170 amp, so i can even run this at the same time. Nothing bad happens, as all devices are monitoring voltage and react accordingly.
The good thing is that you have a battery monitor so you can try it and see.
Just for a test, you could run you engine as well (I assume you have an alternator 3 stage regulator) and see how many amps the batteries will accept when you are at 65%. I am sure it will be more than 130a.

John
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Old 30-11-2009, 16:42   #36
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2 chargers

I have the same question and a new one:

I have two banks, a single group 27 for cranking and 3 group 27s for the house.

I just bought a Xantrex 2000 watt inverter charger that will put 100 amps to the batts. I also have a dual lead 20 amp charger that's almost new I have been using for the 2 banks that works fine but it's slow. I'm about to go cruising for 6 months and wanted a short recharge time, so I got the 100 amp unit.

Quandry #1 Can I use the 100 amp on the bank of 3 and the 20 on the single? I'm connecting the chargers to the batts via the hot sides of the battery selector switch. What would happen if I tie everything together with the 100 amp and the 20 amp by turning the bank selector switch to ALL? Would I fry the 20 amp charger, or simply have 120 amps of charging?

Quandry #2: I also have 2 solar cells. When I put the 100 amp charger on line, will it hurt my solar cells in any way. Do I need to take them out of the loop when I charge heavy. I don't take them out with the 20 amp charger.

I don't want to creamate low flying birds that might come too close to my solar cells with this 100 amp behmouth!...lol Thanks in advance for some wisdom here.

SV "Sea Yawl Later!!"
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