diy solar

diy solar

Debunk: Alternator DC to DC charger not required for big Lithium Battery

Aussieguy said:
if you are unsure of your alternator disconnect the wiring in the BIM which allows the batteries to parallel

I would spend the $$$ first on upgrading the solar
which will be more value for money... works while at the camp site or while driving.
Click to expand...
Yes, solar is the first place to invest. Then a switch to manually manage the connection that you only turn on at highway speeds. Then I will be measuring amperage while driving to see what is really flowing into the LFP house battery.
 
Itechworld lfp batteries are advertised as true drop-in under the bonnet for direct cranking and alterator charging.

The mind ponders....
 
scubadoo said:
Just repeating a previous post of mine on this forum.
Take it or leave it. 9 years full-time on the road and no smoke yet.
The alternator is regulated to 14.5V. I added a Victron Argodiode Battery Isolator in series
a few years ago to limit the maximum output to nearer 14.1V.

Our setup:
The "non smart" original 100A rated alternator in our Mitsubishi Canter 3.9l turbo diesel truck based motorhome has survived 9 years of full-time travel direct charging the 4 cell 300Ah LiFePO4 Sinopoly battery at 70-80A without releasing any smoke yet.
No standard "BMS" circuitry involved.
I recently paralleled a 4 cell 280Ah LiFePO4 EVE battery.
As well as powering our house it has also started the truck perhaps a few thousand times over the years. Perfect performance so far.
The "BMS" involves no charging source exceeding 14.1V at which point the battery is always at 100% SOC regardless of charge current. 80A alternator, 50A solar and 30 battery charger.
20% SOC alarm and Victron BatteryProtect disconnect at 12.5V. Never triggered.
Click to expand...
What gauge wire are you using? How are you able to limit it to 80a of the 100a?
 
trad said:
I haven't seen this discussed here (maybe I can't find it)
Click to expand...

trad said:
This video seems to go against the current state of advice regarding using the alternator to charge lithium directly.
Click to expand...

This is a DIY forum. IMO it is fair to assume that folks interested in DIY have more curiosity, more willingness to experiment, and a higher tolerance for risk than the general retail-buying public.
  • Would I encourage a mouth-breathing, aisle-blocking walmart rando to charge their lithium bank with a relay? Nope. If I had a gun to my head I'd tell them to buy a 20A DC-DC which might not do much charging but can be assumed safe for most alternators and banks.
  • Would I encourage a DIYer who has been successfully charging Pb with a relay and is now upgrading to Li to test how direct-charging actually works in their use case before buying DC-DC? Yes. I would suggest
    • measuring current, chassis voltage, and alternator temp with the existing Pb setup so we have benchmarks
    • adding a switch to disconnect the relay at will, if not already present
    • installing the Li bank and beginning test runs with the bank nearly full and retesting at lower and lower SoC. Compare measurements against with the Pb experience above
I can't accurately predict what will happen in any given case. I can tell you what I have observed in my rig: using a plain VSR my 180A alt charges my 150Ah LFP bank within both current and voltage specs for the battery, and at a rate that is gentle on the alt. 0.2C in middling SoC, ~0.32C when more deeply discharged. ~0.1C when nearly charged. Overall observed current is in the same ballpark as with my original 220Ah GC FLA bank; the main difference is the shape of the taper. The FLA charge acceptance tapered linearly and the LFP taper is very gradual across the broad middle of SoC, which a sudden dropoff as voltage hits the upper knee. I typically disable alt charging at that point.
 
justinm001 said:
What gauge wire are you using? How are you able to limit it to 80a of the 100a?
Click to expand...
The wiring from the alternator to the battery is the original as factory fitted by Mitsubishi.
The alternator delivered c90A by default for about 3 years of traveling trouble free.
For peace of mind I added the Victron Schottky diode isolator about 6 years ago to limit the final maximum charge to 14.1V. It and the associated wiring had the added effect of lowering the maximum current to c80A.
I'm guessing that the slow drop from 80A to nearer 70A over an hour or so is the result of alternator thermal regulation circuitry, battery impedance changes or ???.
It maintains that 70A until almost 100% SOC then rapidly drops to near zero as the battery terminals reach 13.95 - 14.05V.
From 14.0V to the original alternator 14.5V (now 14.1V) occurs rapidly adding no useful energy to the battery. It is already full.

No smoke yet or at least there is still some remaining.
 
100 amps @ idle stopped in traffic vs 100 amps @ 2000 RPM going down the highway.

In case # 2 the underhood air is cooler and the alternator cooling fan is moving twice as much air for the given output.
 
Our 100A rated Mitsi alternator mentioned in the last few posts above spins at c2500 rpm when the 3.9l turbo diesel engine is idling.


3:1 pulley ratio.
 
scubadoo said:
The wiring from the alternator to the battery is the original as factory fitted by Mitsubishi.
The alternator delivered c90A by default for about 3 years of traveling trouble free.
For peace of mind I added the Victron Schottky diode isolator about 6 years ago to limit the final maximum charge to 14.1V. It and the associated wiring had the added effect of lowering the maximum current to c80A.
I'm guessing that the slow drop from 80A to nearer 70A over an hour or so is the result of alternator thermal regulation circuitry, battery impedance changes or ???.
It maintains that 70A until almost 100% SOC then rapidly drops to near zero as the battery terminals reach 13.95 - 14.05V.
From 14.0V to the original alternator 14.5V (now 14.1V) occurs rapidly adding no useful energy to the battery. It is already full.

No smoke yet or at least there is still some remaining.
Click to expand...
Can you check what the alternator model is and if it has a built in regulator or an external? Sounds like you have some thermal regulator or something controlling its field based other measures. Most alternators just use the field to control the voltage and will run at 100% until they burn up.
 
scubadoo said:
Our 100A rated Mitsi alternator mentioned in the last few posts above spins at c2500 rpm when the 3.9l turbo diesel engine is idling.


3:1 pulley ratio.
Click to expand...
This is important to remember, engine RPM does not equal alternator RPM in most cases. pulley ratio adjusts the speed. but to @Checkthisout point 2000rpm engine at 3:1 ratio is 6000 RPM fan on the alternator. Most alternators have a max output amperage well below the engines max RPM so the higher the RPM the better cooling without additional loads on the alternator. Idle 700 RPM might only be 50% of alternator output but 1300 RPM might be 100% and 2000 RPM is still 100%.
 
High resistance in a wire will limit the amps flowing thru to the battery from the alternator due to voltage drop. We had that discussion probably 2 years ago.

Most dc to dc chargers will actually boost the low voltage (circuit resistance) to charge the battery fully.

Now, my favorite saying in these forums. "Just because you can, doesn't mean you should".
 
justinm001 said:
Can you check what the alternator model is and if it has a built in regulator or an external? Sounds like you have some thermal regulator or something controlling its field based other measures. Most alternators just use the field to control the voltage and will run at 100% until they burn up.
Click to expand...
No idea.
I have never seen the alternator in 9 years of full-time traveling.
It is buried in there somewhere.
 
I have a 1/2 ton truck which has a 270-amp alternator and is rated 170 amp at idle. I added a fused wires(dedicated ground wire) from the battery of the truck to an Anderson connector at the back of my truck and ran additional wiring to a Victron 360-watt DC-DC converter mounted in my RV. The wire is high quality 6 gauge. I have used this set up on many trips and have had no issues and am able to charge my LiFePO4 batteries to 14.4 volts. I added this since many of the places where I camp have lots of trees or are in deep canyons and have inconsistent light to charge from solar. I charge when moving from site to site or in an emergency I can run my truck and charge. I disconnect the connector when the truck is not running. The converter does get warm, but I mounted it vertically to improve airflow across the heat sink. I have been very happy with this set up. I have a small trailer, so weight is a limiting factor, so a heavy battery and solar panel load is not an option. However, I would not do this unless you have a large, high-capacity alternator, so for most vehicles it may not be a good option as mentioned in other posts here.
 
100 amps @ idle stopped in traffic vs 100 amps @ 2000 RPM going down the highway.

In case # 2 the underhood air is cooler and the alternator cooling fan is moving twice as much air for the given output.
Click to expand...
I hesitate to add 'pointless' detail but another thing is that the performance of a 'centrifugal impeller' is not linear with rpm so its possible that at some point you spin the fan 20% faster and it functions 50% better. The main idea being, don't load the alternator near max for long periods at low engine rpm. If in doubt, rev higher or just don't do it. If one really wants to know, point a cheap ir pyrometer at the back of the alt and get an actual data point.

One idea i've pondered is that i think a lot of the heat issues with alternators have to do with the fact that the rectifier diodes are dissipating a bunch of heat in a semi circle right around the brushes and the rear case bearing, and then in many cases that heat gets sucked THROUGH the rotor/stator gap (possibly heating both?) and expelled out the fan at the FRONT. I am curious if wiring the stator phases out to an external rectifier would allow a much higher current before the 'next weakest link' became a problem. Infrared camera viewing of a heavily loaded alternator would help sort this out for me. I don't know what the max temp of the stator windings' insulation is, but i figure the brushes are probably the weakest link, followed by the stator winding insulation. Just assumptions, really...
 
I can only comment from my direct experience YMMV.
  • I have 920Ah of LFP installed in my Class A diesel pusher.
  • The batteries are right behind the driver side steer tire.
  • The engine is in the rear.
  • The wires from the house battery are 2/0.
  • They run from the battery compartment to the start battery compartment 30' way, then to the alternator which is another 15'. Total run of 2/0 wire is 2x(30+15) = 90'
  • The 2/0 wires have at least 16 ring terminal connections.
  • I have a BMK battery monitor installed on the house bank to monitor how much current is being received by the house bank,
  • When running with deeply depleted house batteries (-800Ah with resting voltage at 12.5v) the max current received by the LFP batteries was 70Ah with the charging voltage at 13.0v. At the same time, the start battery was receiving 14.4v so there was a 1.4v drop in the 2/0 wire.
  • Per ohms law, this indicates that the resistance in my wiring from the alternator to the house bank was 1.4v/70A = 0.02ohms.
  • I found the alternator to be no hotter than any other component in the engine compartment.
I have no worries that I am over working the alternator because the resistance in the wiring limits the output current to a reasonable level given the 190A output of the alternator.

That said, this is my experience and if I had a gas rig with the house batteries close to the alternator, I would most likely need a different solution. In that case I would install a Li-BIM 225 which opens the circuit to the FLP for a percentage of the time to allow it to cool.
 

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hwse said:
I can only comment from my direct experience YMMV.
  • I have 920Ah of LFP installed in my Class A diesel pusher.
  • The batteries are right behind the driver side steer tire.
  • The engine is in the rear.
  • The wires from the house battery are 2/0.
  • They run from the battery compartment to the start battery compartment 30' way, then to the alternator which is another 15'. Total run of 2/0 wire is 2x(30+15) = 90'
  • The 2/0 wires have at least 16 ring terminal connections.
  • I have a BMK battery monitor installed on the house bank to monitor how much current is being received by the house bank,
  • When running with deeply depleted house batteries (-800Ah with resting voltage at 12.5v) the max current received by the LFP batteries was 70Ah with the charging voltage at 13.0v. At the same time, the start battery was receiving 14.4v so there was a 1.4v drop in the 2/0 wire.
  • Per ohms law, this indicates that the resistance in my wiring from the alternator to the house bank was 1.4v/70A = 0.02ohms.
  • I found the alternator to be no hotter than any other component in the engine compartment.
I have no worries that I am over working the alternator because the resistance in the wiring limits the output current to a reasonable level given the 190A output of the alternator.

That said, this is my experience and if I had a gas rig with the house batteries close to the alternator, I would most likely need a different solution. In that case I would install a Li-BIM 225 which opens the circuit to the FLP for a percentage of the time to allow it to cool.
Click to expand...

great example of when a DC-DC is not needed.
 
sunshine_eggo said:
great example of when a DC-DC is not needed.
Click to expand...
I know how hard it is on an alternator if it runs wide open because I only have about a 6' run of wires from the alternator to batteries on my boat and it would put out the full rated output for +6-hours if I let it and that is in a very hot engine room. In that case, I have external regulator that limit the field current and also has a thermostat that shuts off charging when the alternator's case goes over 200º. I also have an exhaust fan mounted on the fan end of the alternator and a cool air blower on the opposite end to maximize the cooling.

Charging with an alternator CAN cause the loss of magic smoke but as long as you do it right, it works great to maximize the charging current from your engine.
 
Zwy said:
High resistance in a wire will limit the amps flowing thru to the battery from the alternator due to voltage drop. We had that discussion probably 2 years ago.

Most dc to dc chargers will actually boost the low voltage (circuit resistance) to charge the battery fully.

Now, my favorite saying in these forums. "Just because you can, doesn't mean you should".
Click to expand...
The voltage drop is what limits the output but it is the current that creates the drop. When the battery is low, the current will be max and on my coach is self-limiting to about 60A. once the battery gets closer to full, it quits taking so many amps and the voltage drop is less.
To put it a different way, if my LFP batteries need to be charge, I will get 60A and the voltage at the LFP will be 13.0 to 13.4v. If I am coming off the campground and the battery is full, the current to the battery will be nil and the voltage will be 14.4v. No current = no voltage drop.
 
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