On my fourth alternator....??

[wholybee]

Balmar regulators cut field to 50% at 225F/107C. Since they manufacture alternators, that is probably the closest you will find for a manufacturer recommendation. If you have a 160A alternator, a 40A DCDC is very conservative. I would expect you could run at 160A for a few minutes, then cut in half to 80A and be ok, unless there is a cooling/ventilation issue.

 

[Goboatingnow]

Pity you did not ask here before going Lithium.
All sailboats should use lead acid batteries for the engine starter battery for safety and reliability.
If you have a lithium house battery, use a battery to battery charger to charge from alternator power. Your alternator is perhaps a 80A unit, for reliability a B2B in the range 30 to 50 amps should be OK.
The B2B charger connects between the lead acid starter battery and the house battery.

View attachment 105093
For all my marine installs I only use Victron electrical units.


whoever told you that knowing the application, was either untruthful or had no knowledge of marine systems.

Mike

There’s no issue using lithium as a starter like everything you just need to understand the fundementals

 

[roly1]

DIY LiFePO4 Batteries On Boats - Marine How To

DIY LiFePo4 On Boats Last edit;3/26/23:The base of this article was written a number of years ago (2010) but this does not mean the information here is outdated. We have been keeping it updated and have added to it when ever we had the time. This article deals

marinehowto.com

Lithium battery systems | Nordkyn Design

nordkyndesign.com

Read and gain understanding. You have many options which can be hard to evaluate but it’s not rocket science. If not inclined , hire a reputable installer and pay moonbeams for layers of safety that are idiot proof.

 

[Rocketman]

After you get the new alternator, look at cooling the alternator- maybe install another blower that sucks air right by the alternator- thus giving a cooling effect. - leave that blower running during operations.

Good Luck

 

[roly1]

First line of defence should be temperature monitoring by your ext regulator to cut back field and thus
the load on the alternator, reducing windings temp.
I am cost/value conscious and used a Bosch alt out of a Porsche 944 in
which the internal regulator is externally mounted with the brushes. Throw that away (2screws) and install a
brush holder with terminals, then that connects to an external configurable regulator, say mc614, wakespeed or mark grasser.

Secondly, extra cooling so you can increase alternator output by never getting to max temp.
Extra cooling without temp monitoring is building in failure.
The Bosch has a factory hood for external forced cooling, perfect! ($100 ebay for alt and brushes, $300 for mc614)

 

[Marinepower]

First line of defence should be temperature monitoring by your ext regulator to cut back field and thus
the load on the alternator, reducing windings temp.
I am cost/value conscious and used a Bosch alt out of a Porsche 944 in
which the internal regulator is externally mounted with the brushes. Throw that away (2screws) and install a
brush holder with terminals, then that connects to an external configurable regulator, say mc614, wakespeed or mark grasser.

Secondly, extra cooling so you can increase alternator output by never getting to max temp.
Extra cooling without temp monitoring is building in failure.
The Bosch has a factory hood for external forced cooling, perfect! ($100 ebay for alt and brushes, $300 for mc614)

Sounds great.

Pictures?

What's your continuous output at idle or cruising?

 

[hwse]

I Charge LFP on both my sailboat and my motorhome from the alternator without burning up anything. They both use different means of controlling the heat that will build up if not done properly.
On the sailboat, I have a 108A hot-rated alternator that will run fine at 100ºC. I derate the output and provide powered cool outside intake air and exhaust air.
On the motorhome, I the run of wire from the alternator to the battery and back is about 90' so even though it is 2/0 wire, the 160A alternator will not supply more than 60A to the LFP batteries.

 

[Browneye]

Voltage drop doesn’t use less current, it just turns it into heat.

 

[Zapper77]

Voltage drop doesn’t use less current, it just turns it into heat.

I see similar results on my motor home. Due to the 60 feet of wire my Lithium batteries when charged from alternator only receive 13.5v and max out around 20-30 amps. One word of caution when my Lithium batteries are below 13v or I have a heavy load like the microwave, (due to voltage sag) the alternator is able to push 90 amps (2004 Ford 220 amp OEM Alternator). So unless I'm careful and pay attention it's not hard to fry the alternator.

 

[brb58]

That is a fairly common question, with lots of replies in a google search. From cruising forums, to corvettes, trucks, and on and on.
Lots of results for: 'alternator how hot is too hot'.

The general consensus is 70-100C is max. One comment I saw said diodes start to degrade at 70C. That's about 160 degrees F.

If it's smoking it's too hot.

The commercial max temp range for components is typically 70C with industrial grade parts 85C

 

[LeoThomson]

The reason why the alternator fries

 

[brum]

Drop-in replacement exists. At least according to the manufacturer. Here is one - https://dakotalithium.com/product/d...ar-truck-battery-plus-deep-cycle-performance/.

But the price is quite unpleasant...

 

[hwse]

Voltage drop doesn’t use less current, it just turns it into heat.

The way that the system works with long wires is that the voltage at the LFP which is a long way from the source will be 12.0v - 13.5v which is well below the alternators setpoint so it will ask for the max output from the alternator. As the amperage increases, the resistance in the long wire will cause heat and a drop in voltage. Because the wire is so long on my coach, they have about 0.017 ohms of resistance. This causes the alternator output voltage to be about 1volt higher at the alternator than it is at the battery. This causes the internal regulator to limit the current to maintain 14.2v at the alternator which only feeds 60A to the battery. If I turn on a high load like the invertor, this power is supplied by the battery and has no affect on the alternator. On my BMK battery monitor, I will see 60A charging and then when the microwave is pulling a bunch of amps, it will read -100A. The normal load for the microwave is -160A so that works out to 100A from the battery and 60A from the alternator.

 

[hwse]

One other option for charging from the alternator is to use a LiBim on the house circuit. it will limit the charging time by connecting for 15-minutes and disconnecting the alternator 20-minutes from the battery to give it a chance to cool down.

 

[Zapper77]

The reason why the alternator fries

Just remember who produced that video. They provided the test details. They disabled the battery BMS and they tested the alternator at a specific rpm that's typically too low for most gas engines. Comments are also disabled on that video...wonder why.

The ratio in my gas motor home from crank pulley to Alt pulley is 3 to 1. Every revolution of the engine is 3 at the alternator. Engine Idle is 850-900 rpms. Even at idle my alternator is spinning at 2,500 rpms...not 1,500 as shown in their video. Additionally as my 2004 Ford oem alternator heats up it internally limits output current. New vehicles are even worse and the alternators are controlled by the vehicle computer.

While their video is accurate and resulted in their intended results, you should keep in mind that they hand picked an alternator and ran it at less than the designed speed.

From my limited knowledge of boat alternators they are typically just basic low-end and have no built-in safety features. So in this case yes you will melt your boat alternator unless you use some type of charge limiting device.

 

[Skypower]

This is exactly why I told a boat owner, that just because they say it’s a “drop in replacement” and it has the 1000 cranking amps that he shouldn’t be using a lithium starting battery for his 225 Mercury outboard. Run that battery down a bit and the next time he runs that engine he’ll smoke that expensive alternator. Mods are mandatory

 

[brb58]

One other option for charging from the alternator is to use a LiBim on the house circuit. it will limit the charging time by connecting for 15-minutes and disconnecting the alternator 20-minutes from the battery to give it a chance to cool down.

I hate those stupid things. Use a DC to DC converter instead.

 

[Skypower]

I hate those stupid things. Use a DC to DC converter instead.

That doesn’t protect nearly as well as a properly sized DC to DC charge control. Before I’d use LiBim, I’d use a long wire resistance method which I also hate. One gentleman had that without realizing from his truck to his fifth wheel. (Under sized wire that had current/voltage drop under high load, but was within the ampacity to be safe.) Not an accurate method all conditions.

 

[wholybee]

Just remember who produced that video. They provided the test details. They disabled the battery BMS and they tested the alternator at a specific rpm that's typically too low for most gas engines. Comments are also disabled on that video...wonder why.

The ratio in my gas motor home from crank pulley to Alt pulley is 3 to 1. Every revolution of the engine is 3 at the alternator. Engine Idle is 850-900 rpms. Even at idle my alternator is spinning at 2,500 rpms...not 1,500 as shown in their video. Additionally as my 2004 Ford oem alternator heats up it internally limits output current. New vehicles are even worse and the alternators are controlled by the vehicle computer.

While their video is accurate and resulted in their intended results, you should keep in mind that they hand picked an alternator and ran it at less than the designed speed.

From my limited knowledge of boat alternators they are typically just basic low-end and have no built-in safety features. So in this case yes you will melt your boat alternator unless you use some type of charge limiting device.

They could have controlled the test much better. Testing the alternators at different RPMs, and all fairly low speed, just above idle depending on the pulleys uses. (2:1 is common) But the conclusions are not wrong. And running an alternator full-tilt at idle on a boat is common practice for many.

Boats seem to have no "in between" alternators. Either the stock alternator is a dumb, basic, 1970's design, or the owner upgrades to a top-of-the line externally regulated, temperature controlled, marinized alternator. Anyone planning LFP on a boat needs to know what they have, and plan accordingly.

 

[Levo]

This video is interesting.

I have a DC-DC 40A working very well, but I'd be interested to hear other members' opinions on this approach.