Considering an extra alternator for charging the house bank of Trojan T105s.

[GILow]

Hi all,

A month or so into the cruising life, and I’m looking ahead to what is likely to be a cold winter with pretty poor solar input.

My power budget is pretty light, I am guessing I’m going to want to find about 150 AH @ 12 volts on those days that the sun doesn’t shine.

I think the simplest option will be to add an after market alternator to my Beta 50. It comes standard with a 75 amp alternator, but I bet it is the sort that will not sustain 75 amps for long.

I’d like to match the second alternator to my needs and my house bank:

The house bank is a set of 6 Trojan T105s, wired to provide 675AH @ 12 volts.

I usually wake up in the morning with the bank at 85 to 90% full. No problem for the 760 watts of solar if the sun is shining.

Reading the Trojan manual, it would appear that this setup would best be charged with at about 90 amps, or 30 amps per parallel string.

Seems a bit low to me.

I wonder, therefore, where to pitch the alternator capacity. If I fit the 175 amp secondary alternator kit supplied by Beta, for example, how much benefit will I really gain? I suspect the battery bank is going to max out a bit over 100 amps acceptance, but maybe the Trojans are happy to accept more!?

Does anyone have real world experience of the same or similar sized Trojan T105 bank with a big alternator to let me know how much they accept, particularly at these higher charge states.

Matt

[Scott Berg]

Your 675 FLA bank can take a bulk charge of more than .2c. I can start my 50% discharged bank at a charge of 180a and it will quickly slow to 140 till about 75%, and 100a till 80%. Slower from there. I'd recommend you consider at least a 170a alternator derated to 130 or so for temp control/long life. I'm a big fan of Wakespeed controllers... we install a lot of them and our customers love them.

[BillKny]

It will be true that your FLA batteries CAN accept a faster charge than 0.13C. And in the "real world" people do it all the time.

But Trojan didn't pick that number to make your life difficult, they picked it to optimize the lifecycle of the batteries they sell. Charging at a higher rate will use more water, increasing maintenance, and if you aren't good about that, a dry plate is a dead plate. It will also raise the temperature of the batteries much higher than a slower charge, and that greatly shortens their lifespan.

Maximum charge rates are something that people seem to ignore all the time, and in case you haven't noticed there are a lot of threads started by people with batteries dying an early death.

If you want the best experience from your batteries, follow the technical advice of the manufacturer, not random internet people who will eventually give you the answer you most want to hear.

If you want batteries that charge faster, you should have read the spec sheets FIRST and gotten AGM or other fast charging type. Of course if you pump 200 amps into your existing bank you'll be getting those AGM's sooner instead of latter.

[sailorboy1]

I think the extra alternator is a waste of time and might save 20-30 minutes of charging for the times you need to use the engine just for charging.

I use 150-200ah/day. Have 464ah of batteries, 640w solar, a 100a alternator belt reduced to 70 amps. I also have a Honda and a 70 amp charger. I never run the engine just to charge and when i run the Honda it rarely runs an hour before the charger is supplying less than 70a.

Unless your plan is to maintain your batteries less than 80% charge the high amp sources are a waste of money.

[Wotname]

You could whack in another 2 (or 4) T105s (no???). Just fire the engine as required every few days. Don't fit another alternator until you KNOW it is required.

[GILow]

Originally Posted by Scott Berg

Your 675 FLA bank can take a bulk charge of more than .2c. I can start my 50% discharged bank at a charge of 180a and it will quickly slow to 140 till about 75%, and 100a till 80%. Slower from there. I'd recommend you consider at least a 170a alternator derated to 130 or so for temp control/long life. I'm a big fan of Wakespeed controllers... we install a lot of them and our customers love them.

Scott, just to be clear here, is your battery bank the same size and brand?

If so, it suggests that there’s no point in looking at any more than a 100 amp alternator, as I rarely, if ever, get to 80% or below charge state.

[GILow]

Originally Posted by BillKny

It will be true that your FLA batteries CAN accept a faster charge than 0.13C. And in the "real world" people do it all the time.



But Trojan didn't pick that number to make your life difficult, they picked it to optimize the lifecycle of the batteries they sell. Charging at a higher rate will use more water, increasing maintenance, and if you aren't good about that, a dry plate is a dead plate. It will also raise the temperature of the batteries much higher than a slower charge, and that greatly shortens their lifespan.



Maximum charge rates are something that people seem to ignore all the time, and in case you haven't noticed there are a lot of threads started by people with batteries dying an early death.



If you want the best experience from your batteries, follow the technical advice of the manufacturer, not random internet people who will eventually give you the answer you most want to hear.



If you want batteries that charge faster, you should have read the spec sheets FIRST and gotten AGM or other fast charging type. Of course if you pump 200 amps into your existing bank you'll be getting those AGM's sooner instead of latter.

Mate, this is the sort of response that almost makes me give up in despair. You’ve been so anxious to tell me what I am doing wrong that you didn’t actually read the question.

[GILow]

Originally Posted by sailorboy1

Unless your plan is to maintain your batteries less than 80% charge the high amp sources are a waste of money.

That was my gut feeling, but to be clear, are you using the Trojan T105s? For some odd reason I thought you had AGMs?

[sailorboy1]

Originally Posted by GILow

That was my gut feeling, but to be clear, are you using the Trojan T105s? For some odd reason I thought you had AGMs?

I used the t105s for years, but now have Firefly because I got tired of the “need to get to 100%” all the tine.

Mainesail has a write up on charging AGMs that showed that larger charge capacity is mostly wasted because the batteries only accept it at lower state of charge. It is the same for the T105s.

Take the money you were going to waste on this monster alternator and buy a Honda generator instead.

[GILow]

Originally Posted by sailorboy1

I used the t105s for years, but now have Firefly because I got tired of the “need to get to 100%” all the tine.

Mainesail has a write up on charging AGMs that showed that larger charge capacity is mostly wasted because the batteries only accept it at lower state of charge. It is the same for the T105s.

Take the money you were going to waste on this monster alternator and buy a Honda generator instead.

Thank you, that clarifies it a bit.

The Honda is an option, but it would get pricey. I’d have to buy a mains charger, and that would cost more than the alternator. Plus, of course, the Honda itself. If I had more need of mains power the Honda would be a good option.

[smac999]

instead of running the engine every morning when you are at 80 %. do it the next day when you are at 60%. at 60% it'll take the ~150a of the 2nd alt. and your engine run time will be smaller. charge untill ~80% or amps drop down a bunch.

then each day charge from 60-80% with engine if there is no sun. instead of trying to go from 80-100. you will never get to 100% on the engine. or a honda. you need the sun, or a dock for that. from 60-80 each day might be 1 hour of engine running. but 80-100 will be 5 hours of running. no mater how big the alt is.


not getting the batteries to full often is not great. but neither is running the engine for 5 hours charging at 10amps tryin to get from 95 to 100%.

if you get one sunny day a week and get them up to 100 once a week you'd probably be ok.

[wingssail]

I would install a bigger alternator, and for security, keep the original one as a spare.

I think the 174 amp alternator would do well putting out 100 amps for an hour and a half to meet your daily needs when no solar has been available. At that rate the alternator might have a long life.

You could determine the best charge cycle (daily, or alternate days) to meet your power needs.

Many people don't like the idea of charging with your main engine but frankly, that is old advice. My Yanmar has been supplying our power needs for 24 years, now has 6500 hours of mostly charging, and it seems to be in good shape.

I think you will want to invest in a mains charger, probably an inverter/charger at some point for when you are at the dock and it will give you AC power when you are sailing or anchored, very handy.

[GILow]

The alternate charging days idea is interesting.

I do have a lot of solar though, and I feel like, even on the bad days, it should manage things if I give it a head start with the engine in the morning.

I’ll do the alternate charge days thing as a thought experiment over the next couple of weeks and see how it feels.

I already have a Victron mains charger for the dock. At 25 amps it is heaps for my needs at dock, but no good for the Honda approach.

[Wotname]

Originally Posted by sailorboy1

.......

Unless your plan is to maintain your batteries less than 80% charge the high amp sources are a waste of money.

This needs repeating - it is almost always ignored. Once you get into the vicinity 80+% SOC, your lead acid batteries ain't going to take anymore current than what they want - they decide.

You can have fifteen large frame 200A alternators on five engines but your 675Ah bank will still only accept a diminishing current.

There is no perfect solution, batteries are life limited. The best you can do is not kill them prematurely. Treat as best as you can and let them live their allotted life span until they expire.

Once you have as much solar as you can fit / afford and sufficient battery capacity to meet your daily needs, you are at the whim of the sun.

After that, you need to move dockside .

However if you getting into 50%SOC territory and you have a big bank, then yes, you need a big alternator - until then, not so much.

[more]

Originally Posted by GILow

Hi all,

I think the simplest option will be to add an after market alternator to my Beta 50. It comes standard with a 75 amp alternator, but I bet it is the sort that will not sustain 75 amps for long.

I’d like to match the second alternator to my needs and my house bank:
Matt

You can put 1 million amp alternator,or 1 mw generator in dingy ,but your battery bank only accepts current by charging curve your battery chemistry.
I have Winston life battery bank , 150 AH AGM for bow thruster, connected to starter batery downsized from 180 ah to 75 Ah.
2 inverter pure sine one
havy trafo 4000 W surge 12000 w but consume in standby 50w efficiency sucks except 100% capacity i use this for mini wash,dive compressor and icemaker

Now interested for you
have smart 500-1000 w pure sine vave (smart hm, smart is only fan and No-load power consumption: 0,67A 9W)
i conect this inverter to bow thruster (i have battery selector 102 starter-service battery)

and i connect phone charger, laptop charger, and Victron Blue Smart IP22 30A Charger
only solar good MPPT and Blue Smart IP22 Charger & end other marine smart CC curent charger can charge 100%

battery bank . in winter no sun, simple on phone give command Blue Smart IP22 Charger charge 30A or 15A (200-400 Watt) start engine 900-1000 rpm also 100 amp alternator charge 20-30A boath battery bank. take dog for walking - pooping and drink coffee in bar return in boat battery is almost full