Optimal alternator setup?

[justinm001]

Currently I have a 24v 70a alternator set at 27v then have a 24v 270a alternator set at about 28v. The big alternator is oil cooled, industrial and weighs like 100 lbs. Well the field wire came loose on the big one so I'm replacing it and now wondering if there's a better setup.

Currently have 24v chassis batteries and loads connected to small alternator the 4/0 from small to large alt then 2/0 40ft from the mfg to the front where the DC converters are swapping it to my 12 and 48v lfp systems.

I figured if the 270a has a higher voltage the 70a one won't really be doing anything and just sorta backup. Is this correct?

Any other options that'll be optimal? 270a alt alone pumps out like 6500w but since 2/0 I can only use like 145a or 195a which is 3500w or 4600w. I've always been confused on how much power I can safely pull from a cable.

I've also rewired my coach so all my normal loads go through the 12v 5kw inverter the the 48v feeds into this. The 48v feeds 4 of the 6 ACs and other high loads. I'm hoping Victron releases an Orion XS 48/12 and I'll go DC DC smart over DC to AC to DC. I figured if I'm on power reserve I can kill the 48v dual inverters and save 80w draw.

 

[NIFE]

Currently I have a 24v 70a alternator set at 27v then have a 24v 270a alternator set at about 28v. The big alternator is oil cooled, industrial and weighs like 100 lbs. Well the field wire came loose on the big one so I'm replacing it and now wondering if there's a better setup.

Currently have 24v chassis batteries and loads connected to small alternator the 4/0 from small to large alt then 2/0 40ft from the mfg to the front where the DC converters are swapping it to my 12 and 48v lfp systems.

I figured if the 270a has a higher voltage the 70a one won't really be doing anything and just sorta backup. Is this correct?

Any other options that'll be optimal? 270a alt alone pumps out like 6500w but since 2/0 I can only use like 145a or 195a which is 3500w or 4600w. I've always been confused on how much power I can safely pull from a cable.

I've also rewired my coach so all my normal loads go through the 12v 5kw inverter the the 48v feeds into this. The 48v feeds 4 of the 6 ACs and other high loads. I'm hoping Victron releases an Orion XS 48/12 and I'll go DC DC smart over DC to AC to DC. I figured if I'm on power reserve I can kill the 48v dual inverters and save 80w draw.

I have no experience specifically with coach wiring. I am mostly following this but a basic wiring sketch would help. Was the 4/0 wire from the 70A alternator to the 270A unit original or did you add that? Nice to have 2 alternators but I think they should not be tied to each other. You also stated the 48V feeds the 12V inverter. Is there some kind of converter device between them? Does 48V feed the the AC units directly or is it thru an inverter? Also, is the 270A alternator rating a continuous or intermittent rating?

 

[justinm001]

I have no experience specifically with coach wiring. I am mostly following this but a basic wiring sketch would help. Was the 4/0 wire from the 70A alternator to the 270A unit original or did you add that? Nice to have 2 alternators but I think they should not be tied to each other. You also stated the 48V feeds the 12V inverter. Is there some kind of converter device between them? Does 48V feed the the AC units directly or is it thru an inverter? Also, is the 270A alternator rating a continuous or intermittent rating?

Originally the 270a alt used a 12v regulator to make it 12v. It works for lead acid but not lfp. I swapped back to 24v regulator. Also I connected the alternators together using the 4/0. I figured having 4 massive lead acid chassis batteries will help protect the DC converters as lead acid absorbs voltage spikes.

The 270a (Delco 50dn) is continuous rated 100% I believe. They make the same model but a plus that's 450a rated even.

I have 4 24/48v Victron DC DC converters 8.5a. And 2 24/12 Victron DC DC converters 70a. So when driving each gets over 1500w.

The 48v inverters (dual Quattro 5000s split phase) ac output goes into the 12v inverter AC input. So I just switch the 12v inverter from on to invert only if I want to drain the 12v batteries or the 48v.

 

[NIFE]

Originally the 270a alt used a 12v regulator to make it 12v. It works for lead acid but not lfp. I swapped back to 24v regulator. Also I connected the alternators together using the 4/0. I figured having 4 massive lead acid chassis batteries will help protect the DC converters as lead acid absorbs voltage spikes.

The 270a (Delco 50dn) is continuous rated 100% I believe. They make the same model but a plus that's 450a rated even.

I have 4 24/48v Victron DC DC converters 8.5a. And 2 24/12 Victron DC DC converters 70a. So when driving each gets over 1500w.

The 48v inverters (dual Quattro 5000s split phase) ac output goes into the 12v inverter AC input. So I just switch the 12v inverter from on to invert only if I want to drain the 12v batteries or the 48v.

As a starting point, it looks like 40 ft. of 2/0 might be good for 100 amps or less. Being your system is 24V, you may be able to factor in a larger voltage drop. The ~100 amp rating would be in free air, not buried under insulation or inside conduit. Treat your coach electrical system like aircraft. Keep the alternators and their electrical systems separate. That is a pretty big unit. If it is cooled with engine oil, that may be close to a continuous rating.
The UK link below has a wiring calculator.

Cable Size Calculator - Cable sizing and selection | 12 Volt Planet

Cable Size Calculator - Read our guide to selecting cable of the correct type and size for your automotive, marine or leisure wiring application. Auto and Marine Electrical Components from 12 Volt Planet

www.12voltplanet.co.uk

Automotive Wire Amperage Capacity Chart - Jasco Automotive Ltd

AUTOMOTIVE Wire Amperage Capacity Chart Recommended Length and Amperage for Automotive Wire while maintaining a 2% or less voltage drop at 12 volts Automotive Wire Size 5 Amps 10 Amps 15 Amps 20 Amps 25 Amps 30 Amps 20 Gauge Wire (AWG) 4.5 ft 2.2 ft 1.6 ft . 18 Gauge Wire (AWG) 7.3 ft […]

jascoautomotive.com

 

[justinm001]

As a starting point, it looks like 40 ft. of 2/0 might be good for 100 amps or less. Being your system is 24V, you may be able to factor in a larger voltage drop. The ~100 amp rating would be in free air, not buried under insulation or inside conduit. Treat your coach electrical system like aircraft. Keep the alternators and their electrical systems separate. That is a pretty big unit. If it is cooled with engine oil, that may be close to a continuous rating.
The UK link below has a wiring calculator.

Cable Size Calculator - Cable sizing and selection | 12 Volt Planet

Cable Size Calculator - Read our guide to selecting cable of the correct type and size for your automotive, marine or leisure wiring application. Auto and Marine Electrical Components from 12 Volt Planet

www.12voltplanet.co.uk

Automotive Wire Amperage Capacity Chart - Jasco Automotive Ltd

AUTOMOTIVE Wire Amperage Capacity Chart Recommended Length and Amperage for Automotive Wire while maintaining a 2% or less voltage drop at 12 volts Automotive Wire Size 5 Amps 10 Amps 15 Amps 20 Amps 25 Amps 30 Amps 20 Gauge Wire (AWG) 4.5 ft 2.2 ft 1.6 ft . 18 Gauge Wire (AWG) 7.3 ft […]

jascoautomotive.com

The 2/0 is just going to the DC DC converters so voltage loss isn't an issue it's the concern of heat or something else. It's gotta be in large 3in conduit with other wires. I have like 6 tubes going front to back. I'd like to pump as much power as possible but not sure if it's worth swapping to 4/0.

Im not sure if I can run the alt not connected and it just go to DC DC converter. Although if I do this I could ramp up the voltage and pump more through as the DC converters are 18-35v

If I keep them combined I figured it'll protect the smaller alternator and everything else. If separate and the small alternator dies then I'll be stuck on the side of the road.

Another problem is now that my 270a isn't working I have to turn off half my converters because the 70a can't run them all plus my normal coach needs.

 

[NIFE]

I looked at a bunch of electrical ampacity charts. In rather broad terms, most charts show 2/0 is good for 100-140 amps. If you are looking at maxing out the alternator capacity, looks like you definitely need to be at least 4/0. This depends a lot on the insulation temperature rating of the conductor. As far as heat goes, watts =amps x volts. If you get a 3 volt drop at 100 amps, you are generating 300 watts of heat inside the 3 inch, 40 ft conduit. That actually is quite a bit .

 

[justinm001]

I looked at a bunch of electrical capacity charts. In rather broad terms, most charts show 2/0 is good for 100-150 amps. If you are looking at maxing out the alternator capacity, looks like you definitely need to be at least 4/0. This depends a lot on the insulation temperature rating of the conductor. As far as heat goes, watts =amps x volts. If you get a 3 volt drop at 100 amps, you are generating 300 watts of heat inside the 3 inch, 40 ft conduit. That actually is quite a bit .

195 amps at 24v is 5.93% drop or 1.44 volts so 280w. Or 7 watts per foot which I feel like isn't that much. In comparison I'm sure my dash heat and ac lines go through another conduit tube and heat is pumping 200 degree coolant through the same 40ft. It's also possible it's open there's a whole stack of wiring and tubes that goes from front to back.

Voltage Drop Calculator | Southwire

www.southwire.com

2/0 at 90C is rated for 195amps. I'm not sure if the jacket is 95c but I'm assuming it's very good cable just because everything is very well built.



Also I have 20kwh total battery so right now at 3kw/125a it'll take 7 hours to fill from 0 if I bump it up to 4700w/195a it'll take just over 4 hours which doesn't seem that long for heat to cause any issues. And that's from 0%. Although if running ac and other loads it could be full that whole time. But 5-6 hours of driving is kinda my limit anyways.

I don't really know if 300w over 40ft inside sch40 pvc conduit is safe or something to be on the look out for. I'm also guessing on the size being 3in, could be 2 or 4. There are openings in places too as some wires are coming/going in various bays.

But I'm thinking you're right and I should just keep the 125 max amps and call it a day. Plus it's frame grounded which seems like a bunch

 

[NIFE]

Was the 270A alternator and 2/0 wire original from the factory or added at a later time. If original, what was it feeding back when new?
It seems to be pushing the limits connecting 270A to 2/0 wire. It would be ok for a very short term (minutes) but not continuous unless it was designed to be running the wire/insulation/crimps/terminals at a high temperature. We have a lot of winter visitors here. I occasionally see motor homes in flames on I-17 and wonder how that happened. They appear to not start in the engine compartment either..

 

[justinm001]

Was the 270A alternator and 2/0 wire original from the factory or added at a later time. If original, what was it feeding back when new?
It seems to be pushing the limits connecting 270A to 2/0 wire. It would be ok for a very short term (minutes) but not continuous unless it was designed to be running the wire/insulation/crimps/terminals at a high temperature. We have a lot of winter visitors here. I occasionally see motor homes in flames on I-17 and wonder how that happened. They appear to not start in the engine compartment either..

Yes the 270a alt was from factory. Idk if factory or converter ran the 2/0 wire, assuming converter did as they handle house system. It was connected to 4 or 6 huge 8d batteries. I'm sure they didn't expect to use close to 270a for that install. The coach has a bus air option where that 270a alt powers 225k btu aircon when driving and uses a 3rd alt for house.

It seems like a ton of work to try and swap that 2/0 to 4/0. If anything I'd add another 4/0 wire going right to the 48v bay which is in the middle then just move those 48v converters over.

 

[NIFE]

The hard part is done. You have a factory installed large alternator that apparently is rated for 100% continuous duty. I looked at the Delco factory spec. They claim 80% output at idle speed. That is pretty impressive. It would be nice to use all that safely.

 

[jberger]

Unless you have a dual alternator controller like the Balmar centerfielder, I think you need to separate the alternators.
Run the smaller alternator for your engine battery bank and wire the 50DN to the House.
I think you run the risk of burning out both units when the batteries are charged or if there is a BMS disconnect with the current topology.
The 50DN puts out a lot of current at idle, so it could completely overpower the smaller alternator at idle or low speed.

I upgraded from the 50DN to an Almott 400a air cooled and use a controller to connect and disconnect the Engine and House battery banks based on load. Since the alternator is always connected to the AGM Engine bank, I don't worry about any flyback current taking out the voltage regulator or the alternator. The 50DN is a great unit, I just had repeated issues with leaking oil, and my last refurb started leaking in less than 5,000 miles. I still have it on the shelf just in case but I moved to air cooled so I didn't have to worry about it. Taking it out of the oil loop also gave me more oil pressure too (just something to think about).

Putting a DC to DC charge controller at the 50DN would let you regulate the amperage on the long run cabling to make sure you don't overload it. I ran new 4/0 and covered it in PET braided wire loom so I didn't have to worry about it for years.

 

[justinm001]

The hard part is done. You have a factory installed large alternator that apparently is rated for 100% continuous duty. I looked at the Delco factory spec. They claim 80% output at idle speed. That is pretty impressive. It would be nice to use all that safely.

Yeah at idle it doesn't drop .1volt when pumping over 3000w. Now it's not working and just using the 70a one it struggles pumping 1000w and I have to run just 1 70a converter and turn it off when I drive in the city.

 

[justinm001]

Unless you have a dual alternator controller like the Balmar centerfielder, I think you need to separate the alternators.
Run the smaller alternator for your engine battery bank and wire the 50DN to the House.
I think you run the risk of burning out both units when the batteries are charged or if there is a BMS disconnect with the current topology.
The 50DN puts out a lot of current at idle, so it could completely overpower the smaller alternator at idle or low speed.

I upgraded from the 50DN to an Almott 400a air cooled and use a controller to connect and disconnect the Engine and House battery banks based on load. Since the alternator is always connected to the AGM Engine bank, I don't worry about any flyback current taking out the voltage regulator or the alternator. The 50DN is a great unit, I just had repeated issues with leaking oil, and my last refurb started leaking in less than 5,000 miles. I still have it on the shelf just in case but I moved to air cooled so I didn't have to worry about it. Taking it out of the oil loop also gave me more oil pressure too (just something to think about).

Putting a DC to DC charge controller at the 50DN would let you regulate the amperage on the long run cabling to make sure you don't overload it. I ran new 4/0 and covered it in PET braided wire loom so I didn't have to worry about it for years.

I thought a centerfielder or similar only helps the alternators communicate together to maximize output. Right not they both have their own controllers and the 70a is lower voltage than the 270a. I figured this is ideal so the 270a will overpower and leave the 70a basically sitting idle ready to go.

I like the oil cooled as it keeps the alt at perfect temps and since my coach is severely over built with oil cooling and everything it seems most efficient at keeping engine bay cool.

I don't think I'm losing oil from that but could be, im also replacing my 50dn this week since the field lug is broken (unless there's an easy way to swap that out). I'm worried about opening it up and braking something and causing a oil leak.

I do have an oil leak or something going on. It's on my list. The rear of the coach gets oil all over like crazy. The exhaust is rusted and no tip so I'm hoping that the exhaust is going all into the engine catching the oil from it and sprinkling it out the back... But Idk. I haven't checked oil and fluids in a while it's also on my list.