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Old 24-05-2016, 11:02   #1
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Alternator Wire Size

I've got a 24V 140 Amp Alternator that we just installed. It will be controlled by a Balmar 624 regulator and it is about 12' of wire from the Alternator to the battery. 380Ah LiFePo battery. So I tried out Blue Seas nifty wire sizer App and input the following: 24V, 140A, Length of Conductor (Round Trip) 24', 3% Voltage Drop, Insulation Temp Rate 105, Installed in Engine Room, Wires in Bundle 2-3, 120 minute duration and (Of Course) it is terminated in a fuse.

The App gave me the following:
Voltage Drop (ABYC) AWG 3
Ampacity (ABYC) AWG 1
Ampacity (Blue Sea) AWG 3/0

So with a possible range of AWG 3 to 3/0 I though wow, that is interesting 3/0 seems crazy big.

So said what if it is not terminated in a fuse?? This changed the Blue Sea recommendation to AWG 1. That is a huge change just because I've got a fuse in at the charge bus.

So next I said well let's see if I can stand a 10% Voltage drop. After all the alternator will be regulated to provide the needed voltage at the battery. This changed the Voltage drop size to AWG 8. However just by Ampacity I still need AWG 1. Makes sense.

Since the Alternator output will be reduced to about 100 to 120 amps with the "belt manager" to avoid cooking it. I think I am comfortable with the AWG 1 wire size. I'll probably put a 150Amp ANL or MRBF type fuse on it.

Any thoughts from the forum here?

Thanks to all.
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Old 24-05-2016, 18:37   #2
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Re: Alternator Wire Size

3/0 is super uncommon. 2/0 would be just fine. is the alt an isolated ground? because only if it is do you really have a true round trip. because it's using the engine cable anyways. (which may or may not already be big enough.

fuse it at 200a at the battery end. 150 is too small for a 140a alt. the MRBF's are good for this.

1awg is also not very common.

if you're going to reg it down to 120a. 1/0 would probably be good. aim for 3% for the alt.
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Old 24-05-2016, 20:44   #3
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Re: Alternator Wire Size

Putting what I thought were your parameters into the Blueseas web based calculator, not the app, came up with more like awg 2 depending on how I play with options.
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Old 24-05-2016, 23:15   #4
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Re: Alternator Wire Size

Why could this sailor, not run this to the hot side of the starter solenoid.?


Still surrounded by anchors.
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Old 25-05-2016, 06:00   #5
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Re: Alternator Wire Size

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Originally Posted by lonesoldier0408 View Post
Why could this sailor, not run this to the hot side of the starter solenoid.?


Still surrounded by anchors.
Thanks for the suggestion. Starter soleniod is connected directly to the start battery which lives in the engine room. There is another 4/0 connection that can be engaged in the event the start battery is low.
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Old 25-05-2016, 06:04   #6
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Re: Alternator Wire Size

Quote:
Originally Posted by Paul L View Post
Putting what I thought were your parameters into the Blueseas web based calculator, not the app, came up with more like awg 2 depending on how I play with options.
I just did the same thing and also came up with the same 2 AWG wire size. If I put it in conduit or a sheath it goes up to 2/0. It is very odd the two applications are not identical. Anyone else tried them?
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Old 25-05-2016, 06:20   #7
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Re: Alternator Wire Size

Conduit retains the heating from the current flow. So thicker wire to reduce heat generated. In free air the heat dissipates readily, so thinner wire is acceptable. The insulation on the wires has a max temperature rating, hence the difference.
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Old 25-05-2016, 07:10   #8
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Re: Alternator Wire Size

Off topic a little but what is the pulley size on the alternator? Many of these large alternators never see the RPM required to attain maximum output as the are not turned fast enough. Usually they will come with a 60mm diameter pulley which cannot be reduced any further unless it is a serpentine drive and even then you are limited.

I have a 200 amp 12v alternator with an external Balmar regulator for charging the house bank when motoring and never see anywhere near 200 amps even when I rev the engine to 2100 rpm. Typical output is 75-85amps at 1600 rpm. Lost the genset for a week recently and had to charge house bank with main engine and almost got as much output from the engine alt as the larger 200 amp alt.

Might be worth looking into so you are not disappointed with the outcome.
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Old 25-05-2016, 07:34   #9
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Re: Alternator Wire Size

Quote:
Originally Posted by lonesoldier0408 View Post
Why could this sailor, not run this to the hot side of the starter solenoid.?


Still surrounded by anchors.

That is what I did, and I put the battery switch to "All" and it works fine.
Seeing as how several have told me its a matter of time before i screw that up, I bought a charge combiner or whatever its called that I assume just connects the two banks together when charging, I have yet to install it, but as opposed to running that huge and expensive wire, I don't see the downside?

http://www.amazon.com/Blue-Sea-Syste...ilpage_o05_s00
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Old 25-05-2016, 15:13   #10
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Re: Alternator Wire Size

Undercutter,

Alternator is a BLD3314GH from Leece Neville. The pulley on the alternator is 3" and the crank shaft is 7.5" giving me a ratio of about 2.5. We cruise around 1400 to 1600 rpm so the alternator RPM is 3500 to 4000. So we are in the +120 amp range based on the alternator curve attached. I've also got to keep in mind that Wide Open Throttle is 2800 rpm or 7000 rpm which is a little higher than the max recommended. We don't cruise wide open ever. Occasionally for a few minutes to make sure all is in order and exercise the diesel.

It is all a bit of an experiment, but much improved from the original std alternator. Attached the RPM vs amp curve for this alternator for information too.
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Old 25-05-2016, 15:31   #11
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Re: Alternator Wire Size

Quote:
Originally Posted by JBPohle View Post
I've got a 24V 140 Amp Alternator that we just installed. It will be controlled by a Balmar 624 regulator and it is about 12' of wire from the Alternator to the battery. 380Ah LiFePo battery. So I tried out Blue Seas nifty wire sizer App and input the following: 24V, 140A, Length of Conductor (Round Trip) 24', 3% Voltage Drop, Insulation Temp Rate 105, Installed in Engine Room, Wires in Bundle 2-3, 120 minute duration and (Of Course) it is terminated in a fuse.

The App gave me the following:
Voltage Drop (ABYC) AWG 3
Ampacity (ABYC) AWG 1
Ampacity (Blue Sea) AWG 3/0

So with a possible range of AWG 3 to 3/0 I though wow, that is interesting 3/0 seems crazy big.

So said what if it is not terminated in a fuse?? This changed the Blue Sea recommendation to AWG 1. That is a huge change just because I've got a fuse in at the charge bus.

So next I said well let's see if I can stand a 10% Voltage drop. After all the alternator will be regulated to provide the needed voltage at the battery. This changed the Voltage drop size to AWG 8. However just by Ampacity I still need AWG 1. Makes sense.

Since the Alternator output will be reduced to about 100 to 120 amps with the "belt manager" to avoid cooking it. I think I am comfortable with the AWG 1 wire size. I'll probably put a 150Amp ANL or MRBF type fuse on it.

Any thoughts from the forum here?

Thanks to all.
John,

You are charging LFP batteries which at rest or a light load will be in the 26.6V (3.325VPC) - 26.8V (3.35VPC) range. If you are charging to safe LFP voltages such as 27.6V (3.45VPC) to 28V (3.5VPC) you barely have any room for voltage drop. I would not advise charging above 28V (3.5VPC).

FWIW I have a totally destroyed $10,000.00 24V LFP battery on my bench that was charged to 3.65VPC. It is now a 10K pile of scrap heap junk, do not do this to your battery... That manufacturer now advises 3.55VPC and this is still 100% unnecessary and will only lead to future problems. Their answer to my customer about the destroyed battery? Sorry the cells are balloons, it was over-charged you're not covered. This is the second LFP battery I have seen in my shop destroyed by improper high voltage charging..

A 3% voltage drop on 28V is 0.84V without any terminations fuses etc. accounted for. With LFP between resting/working voltages and full charge you only really have about 1V to 1.4V to play with. Voltage drop in LFP is not like lead where you have 5V to play with between 50% SOC and charge voltage. You really can not afford much if any voltage drop in LFP if you expect charge performance.

What I am getting at is to use the largest pos & neg wire you can, for the least drop, and then be 100% positive your regulator volt-sense positive and Black/B- wire sense directly at the LFP banks terminals. I am of course assuming the alternator is feeding the LFP bank directly and has a proper HVC which interrupts the regulator B+ wire...
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Old 26-05-2016, 19:12   #12
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Re: Alternator Wire Size

BLD3314 Spec's, still figuring out how to upload pictures. How do you post a picture directly so it doesn't have to be opened?
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Old 26-05-2016, 20:01   #13
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Re: Alternator Wire Size

Mainesail thanks for the detailed reply. It was very timely since I am just working on balancing my new cells right now. I've got the HY3030EX parallel charging 8ea CALB CA180's. Been working on it for a week. Batteries all came at 3.28 volts. 30 amps into 8 cells results in only 3.75 amps per cell, so its a slow roll. So after a week off and on, when I am on the boat supervising, we are up to 3.345V and have reached the CV phase which I set to 3.6V. Interestingly I've got 0.25V loss from the terminals on the power supply to the terminals on the battery. Yep that's about a 7% voltage drop. I figured the voltage drop will get less as the amps drop off.

The CALB manual, at least what EVTV published, recommends terminating the CC/CV charging of the CA180's at 9amps and 3.6volts. So I am not sure when I am going to stop the top balancing. We're trickling in the amps so to take to 3.6 doesn't seem prudent. So I think I'm going to let the amps drop to 2 amps/cell at whatever voltage we get to.

All this completely illustrates how voltage loss can lead to problems so I am going to stick to <3% as advised for wire size.


You are charging LFP batteries which at rest or a light load will be in the 26.6V (3.325VPC) - 26.8V (3.35VPC) range. If you are charging to safe LFP voltages such as 27.6V (3.45VPC) to 28V (3.5VPC) you barely have any room for voltage drop. I would not advise charging above 28V (3.5VPC). Absolutely, just starting to put together the program for the Balmar 624 and also the Victron Quattro 5000/24.

FWIW I have a totally destroyed $10,000.00 24V LFP battery on my bench that was charged to 3.65VPC. It is now a 10K pile of scrap heap junk, do not do this to your battery... That manufacturer now advises 3.55VPC and this is still 100% unnecessary and will only lead to future problems. Their answer to my customer about the destroyed battery? Sorry the cells are balloons, it was over-charged you're not covered. This is the second LFP battery I have seen in my shop destroyed by improper high voltage charging.. Ouch thanks for helping the rest of us keep out of trouble. Was that a charge profile that terminated at high amps still or did it end in trickling in the amps?

A 3% voltage drop on 28V is 0.84V without any terminations fuses etc. accounted for. With LFP between resting/working voltages and full charge you only really have about 1V to 1.4V to play with. Voltage drop in LFP is not like lead where you have 5V to play with between 50% SOC and charge voltage. You really can not afford much if any voltage drop in LFP if you expect charge performance.

What I am getting at is to use the largest pos & neg wire you can, for the least drop, and then be 100% positive your regulator volt-sense positive and Black/B- wire sense directly at the LFP banks terminals. I am of course assuming the alternator is feeding the LFP bank directly and has a proper HVC which interrupts the regulator B+ wire...[/QUOTE] Yes we will be charging directly from the alternators to the battery on a charge bus and will have the HVA relay terminate the ignition input. The 624 doesn't have a voltage sense wire for the battery, so we'll run a much larger wire for the regulator power wires to keep this loss to a minimum.

Thank you again for the thoughtful response.
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Old 27-05-2016, 04:13   #14
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Re: Alternator Wire Size

Just a heads up... the Balmar 624 regulator does NOT have remote voltage sense, so it won't compensate for voltage drop between the alternator and batteries. The 12V version does, but for some unknown reason the 24V version doesn't. The wire that powers the device is also the sense.

This leaves you with 2 ways to wire it up, each with tradeoffs. You can wire it to the alternator + terminal as recommended by Balmar, but understand that you may need to tweak your charge voltage to compensate for loss in the cables.

The other way to do it is to run a cable and power it directly from the battery. Then it will sense battery voltage, but you again need to size the wires for the current draw of the Balmar itself, including the field current for your alternator. The cable won't be 2/0, but it will probably end up a lot bigger than you expect. I would strive for 1% voltage drop.

Personally, I would use at least 2/0 for the alternator cables, and probably go with 4/0 unless there was something that made it impossible.
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