Running Two Alternators

[mesquaukee]

I have 2 alternators. One (150 Amp) is regulated by a Xantrex regulator.
The other one (90 amp) has a switch on it that bypasses the internal regulator. Should I wish to have a high charging current I flip the switch and it charges at full output, the regulated alternator regulates the voltage, after a period of time I turn it off (when charging rate decreases).

[S&S]

Originally Posted by David M

I think its getting unnecessarily complex. The downside to complexity is the increased chance of failure.

Dunno- doesn'y seem overly complicated to me.
In any event, the good folks at C.E. Niehoff have a fine 400A alternator which should be good for the house bank. At 80% discharge it'd fill it in 3.2 hours ( I'm neglecting the tail). 215A at idle (wow!)

Here's the options:

1) Easy Peasy- big alternator charges house bank, little one on the engine is for the start bank only- essentially two seperate systems.

2) More complicated, but pretty straightforward- wire them so either Alt can charge either bank. If I go with all LiFePO4 it'd still be pretty simple- if I mix chemistries I think that I can still use the charge regimen for LiFe to charge AGM's ( I have to confirm this but I heard it from two regulator Mfr's.) I like the redundancy.

3) Electrical artistry: Either, or or both- ability to link them up. Westerbeke says I can get 190A on the engine so 590A total if combined but the regulation gets more complicated- I'm not going there if I'm mixing chemistries. It'd save me about 1 hr of run time (2.2 hrs from 80% discharge)

So: Which option do you all recommend.

[s/v Jedi]

Think about the wiring. At 600A you need 4 times 4/0 cable (2 red plus 2 black).

Anyway, I would keep it separate, standard alternator just for starter bank and 2 big ones (2 x 200A if you want 400A) that cancel each others side-pull so the engine bearings survive it. Connect their fields together using one regulator that has enough oompf to feed that (Ample Power SARv3, you need 15A field current rating on the regulator)

cheers,
Nick.

[S&S]

Originally Posted by s/v Jedi

Think about the wiring. At 600A you need 4 times 4/0 cable (2 red plus 2 black).

Anyway, I would keep it separate, standard alternator just for starter bank and 2 big ones (2 x 200A if you want 400A) that cancel each others side-pull so the engine bearings survive it. Connect their fields together using one regulator that has enough oompf to feed that (Ample Power SARv3, you need 15A field current rating on the regulator)

cheers,
Nick.

Good except:
1:The engine mount alt is already on one side
2: I have no extra room on the port side of the engine and tons of room on the starbord side
3: I'll have to check if the SARv3 will charge LiFe cells.
4: Even so, I need to regulate idle output because the alt will see a dead short at idle as the cells have a very low internal resistance- the Niehoff rep said they have a regulator (it's a military product so I'll have to figure a way to get one) that senses alt temp and will cut the field at idle to prevent overheating. Also I need an overvoltage tap to hook to the battery manager which I'm not sure AP provides. I'll give them a call though.

Niehoff has a ready made rig with 2 300A alts for 600A (common regulator)

I have a straight run to the bank so 2 x 0000 isn't an issue. I'd use 2 x 000 anyway at 400A- I'll bus between cells.

I'm leaning toward "Option 2" as the most versatile. (Man, this is getting interesting )

[s/v Jedi]

You can NOT put 400A worth of alternators on one side of the engine without wearing down the engine's bearings quickly. As you have no room at the other side, you will either have to settle for a lower output, like under 200A, or find another way to charge the batteries, like a genset.

I know a 3rd way now I think of it: Replace the stock alternator with a hydraulic pump and mount a 2nd one on the available space on the other side. Use a hydraulic motor to power the mother of alternators and echo charge the starter battery from that source.

Very low resistance does not create a dead short. A dead short is a 0-Ohm connection, which is very different from very low resistance. As long as the battery has a voltage on it's posts, it has internal resistance and the more it is charged, the more resistance it gets. But you might be right that normal alternators will burn up charging those babies. There's only one solution I know for that and that's pulse-width modulation on the alternator field (switch it on&off all the time). The duty cycle of this PWM modulation would be controlled by the temperature of the alternator housing. This is no secret military technology. A first year electronics student can built it for you if it's not available yet.

How are you supposed to charge these batteries? What information does the manufacturer provide you with. They should point you to the right kit for it when they want to sell batteries!

You will also have to mount the alternator diodes externally on a heatsink with forced air cooling (it probably already is like that for 400A alternators).

Yes, we use doubled-up 4/0 for 400A service on Jedi. I didn't find much boats with more engine-mounted charging power, so I'm interested how you fare! ;-)

ciao!
Nick.

[mesquaukee]

If you have some room on the front of the engine you can add a frame that allows you to take off as much power as you want and solve the side load problem of the bearings, see attached sketch.
Alignment of the shafts is simple as the pillow blocks can be moved laterally.
Since the frame traps the belt for the water pump wire tie a couple of spare belts to the frame. You do not want to have to remove the frame to install a new belt.

[S&S]

Originally Posted by s/v Jedi

You can NOT put 400A worth of alternators on one side of the engine without wearing down the engine's bearings quickly. As you have no room at the other side, you will either have to settle for a lower output, like under 200A, or find another way to charge the batteries, like a genset.

What I can do is put a layshaft on the other side and tension a belt to it. Won't drive anything but would relieve some of the side loading.

Very low resistance does not create a dead short. A dead short is a 0-Ohm connection, which is very different from very low resistance. As long as the battery has a voltage on it's posts, it has internal resistance and the more it is charged, the more resistance it gets. But you might be right that normal alternators will burn up charging those babies. There's only one solution I know for that and that's pulse-width modulation on the alternator field (switch it on&off all the time). The duty cycle of this PWM modulation would be controlled by the temperature of the alternator housing. This is no secret military technology. A first year electronics student can built it for you if it's not available yet.

I know the tech isn't secret, the issue is whether they can sell it to me (stupid regs). It's not a true 0 ohm load but for practical purposes there isn't enough resistance to keep the alt from overheating at idle.These dont work like PbA batteries- the internal resisitance is very low and the back voltage doesn't rise until the very end of the charging curve. I think this is simpler- a varistor coupled to a temp sensor ramps the field current down. I have to have another conversation with the rep.

How are you supposed to charge these batteries? What information does the manufacturer provide you with. They should point you to the right kit for it when they want to sell batteries!

The normal mode for these is a line voltage charger so alt charging is new territory.

You will also have to mount the alternator diodes externally on a heatsink with forced air cooling (it probably already is like that for 400A alternators).

that's part of the alt design so no worries there

Yes, we use doubled-up 4/0 for 400A service on Jedi. I didn't find much boats with more engine-mounted charging power, so I'm interested how you fare! ;-)

ciao!
Nick.

Good man, you can't get in trouble going up in wire size.

[S&S]

Originally Posted by mesquaukee

If you have some room on the front of the engine you can add a frame that allows you to take off as much power as you want and solve the side load problem of the bearings, see attached sketch.
Alignment of the shafts is simple as the pillow blocks can be moved laterally.
Since the frame traps the belt for the water pump wire tie a couple of spare belts to the frame. You do not want to have to remove the frame to install a new belt.

As above, I don't have too much room on the front but I could either:
1. Put a dummy layshaft on the other side to relieve some loading or
2. I may be able to do a PTO like what you show, but I'll have to figure a different frame design to make it easier to get belts on and off (and clear everything else).
Thanks!

[S&S]

Talked to Westerbeke and max side load is 6hp or about 200A. So a bracket it is. I think there are mounting points on the front of the engine that will work and they are checking into it now.

[btrayfors]

FWIW, 6 horsepower = 6 x 745.7 watts = 4474.2 watts / 13 volts = 344 amps.

[S&S]

Originally Posted by btrayfors

FWIW, 6 horsepower = 6 x 745.7 watts = 4474.2 watts / 13 volts = 344 amps.

At 100% conversion efficiency. Would be nice,wouldn't it.
Anyway, I'm merely quoting the guy from Westerbeke and it's not good practice to engineer "to the edge" anyway

[Cheechako]

"C.E. Niehoff have a fine 400A alternator which should be good for the house bank. At 80% discharge it'd fill it in 3.2 hours..." No it wont, your batteries limit what can be put in ! You could have a 1000 amp alternator, but your batteries wont take it for more than a minute or two! or maybe you have a 5000 amp bank?

[S&S]

Originally Posted by Cheechako

"C.E. Niehoff have a fine 400A alternator which should be good for the house bank. At 80% discharge it'd fill it in 3.2 hours..." No it wont, your batteries limit what can be put in ! You could have a 1000 amp alternator, but your batteries wont take it for more than a minute or two! or maybe you have a 5000 amp bank?

They are not lead acid batteries. With LiFePO4 the charge rate is 3C up to over 90% charge. Which I believe I mentioned before.

Ain't new technology wonderful?

[Cheechako]

hmmm.... I stand corrected... interesting....so how much can those take for how long? I dont think the load on the enigne is going to be an issue as keeping the diesel loaded up adequately is more the problem when recharging right?... however the side load could be an issue....

[btrayfors]

Originally Posted by S&S

At 100% conversion efficiency. Would be nice,wouldn't it.
Anyway, I'm merely quoting the guy from Westerbeke and it's not good practice to engineer "to the edge" anyway

Absolutely right! At the 60% efficiency typical of car and many marine alternators, that's 344 x .6 = 206 amps. Surprise :-)

Sounds like a fun project.

B.