General questions about alternator charging

SeattleNewbie

2013 NCV3 2500 170" WB
I'm playing with the idea of charging our 200 AH house battery bank (two x 100 AH LiFePO4 BattleBorn batteries) using the current generated by the Sprinter alternator. My system diagram is here:

https://docs.google.com/drawings/d/11bQNj6b6N-zwF_2teqO6HNCvf-l3wURnMc1h1YpPFvk/edit?usp=drivesdk

1. What are the practical limits to how much current I can expect to draw from the NCV3 alternator?

My datamb.com profile claims that we should have a 220 A alternator: "14 V/220 A ALTERNATOR"

Though presumably some / most of the current is needed for running various systems in the van. Is that a valid assumption?

2. I understand that one way to accomplish my goal is to install a DC-DC charger such as these Renogy devices:
https://www.renogy.com/12v-dc-to-dc-on-board-battery-charger/

Are they downsides to this approach?

Are there substantially superior dc-dc chargers which I ought to research?

3. Are there other / "better" ways to accomplish this goal?
 

sparkplug

Well-known member
I'm going to answer this post even though I'm a lot less knowledgable than many on here when it comes to electrics. My reason for doing so is that I have a working solution in my van so am happy to share my personal experience.

1. Newer NCV3 alternators are 'smart' alternators and will sense the amount of load and adjust their output accordingly. In the real world I think that your 220A alternator is never going to struggle to charge your house batteries. Unless your vehicle battery is failing you should be OK. Yes, some of the power will be needed by the van but the extra load demanded by the house batteries will simply make your alternator generate the extra current required.

2. Yes. When I installed mine I didn't have very much knowledge and didn't really do as much research as I perhaps should have done. I have a Duritic Voltage Sensitive Relay (VSR) which is not as good as a DC-DC (aka Battery to Battery or B2B system) - however it still works absolutely fine for me as I have an older 'dumb' alternator. VSRs will NOT work with 'smart' alternators. I am not aware of any downsides to this approach. Renology seem to have a good reputation in the US. In the UK I hear of a lot of people using the Sterling B2B units. There's an article which I found quite helpful here

3. Other ways to accomplish charging your house batteries? I don't know of any unless you want to include solar or shore power as potential options. I have a mix of solar and VSR and I can get 4-6 days of 'off grid' power from my 2 x 110AH batteries (not LiFePO4 so only about 110 useable AH) without driving to charge. Of course that depends on which solar panels you have, how much sun you get, how much power you use... but in broad terms I think you could fit a renology to your current set up and not really have to worry about your house batteries as long as you don't plan to park up for prolonged periods without driving the van or topping them up with an alternative power source.
 
B

billintomahawk

Guest
3. Other ways to accomplish charging your house batteries? I don't know of any unless you want to include solar or shore power as potential options./QUOTE]

You can power a pure sine inverter from the vehicle 12 volt system. Use the 120 volt AC output to power a shore power charger. That way you can get a proper 3 stage charge profile.

https://www.ortontransit.info/electrical
Hey Dave, just trying to understand the physics.

So I have to think about this but basically what I think you are saying is that you can take 13.3VDC in a house battery and convert is to AC and run an AC charger outputting DC at a higher voltage(less Amps)and boost the DC charge to say 14.3VDC to profile charge your house battery using a smart charger.

Is that how it works?

I'd be going from solar panel to house battery to pure sine wave inverter to AC charger making DC back to battery via smart charger.

Good thing electrons travel at the speed of light.

bill
 
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calbiker

Well-known member
So far I have nothing but praise for the 40A Renogy B2B charging a 180AH LiFePO4 battery. I've found lower amp charging is better than say 50A. You will get a more complete charge as the internal BMS will get fooled by cell resistance (IR drop), believing the cell is full when it is not.

Can't beat the $110 price for a 20A B2B. No need for a temp sensor.
 

Graphite Dave

Dave Orton
Hey Dave, just trying to understand the physics.

So I have to think about this but basically what I think you are saying is that you can take 13.3VDC in a house battery and convert is to AC and run an AC charger outputting DC at a higher voltage(less Amps)and boost the DC charge to say 14.3VDC to profile charge your house battery using a smart charger.

Is that how it works?

I'd be going from solar panel to house battery to pure sine wave inverter to AC charger making DC back to battery via smart charger.

Good thing electrons travel at the speed of light.

bill
No. That is not how it works.

The vehicle powered inverter output is switched to power the shore power 3 stage charger. 12 volt power comes from the vehicle 12 volt system. The inverter is powered by the vehicle 12 volt system and is not powered by the house battery.

The other uses for the 120 volt power (with engine running) are to heat shower water electrically or to power a 750 watt air heater.

Charging with the shore power charger powered by the vehicle powered inverter is my backup method of charging if weather conditions force its use if the 300 watt solar panel does not keep up with electrical usage.
 

OrioN

2008 2500 170" EXT
I'm playing with the idea of charging our 200 AH house battery bank (two x 100 AH LiFePO4 BattleBorn batteries) using the current generated by the Sprinter alternator. My system diagram is here:

https://docs.google.com/drawings/d/11bQNj6b6N-zwF_2teqO6HNCvf-l3wURnMc1h1YpPFvk/edit?usp=drivesdk

1. What are the practical limits to how much current I can expect to draw from the NCV3 alternator?

My datamb.com profile claims that we should have a 220 A alternator: "14 V/220 A ALTERNATOR"

Though presumably some / most of the current is needed for running various systems in the van. Is that a valid assumption?

2. I understand that one way to accomplish my goal is to install a DC-DC charger such as these Renogy devices:
https://www.renogy.com/12v-dc-to-dc-on-board-battery-charger/

Are they downsides to this approach?

Are there substantially superior dc-dc chargers which I ought to research?

3. Are there other / "better" ways to accomplish this goal?
The advantage of using the alternator with its upper voltage limit of ~14.1V with a LiFePO4 bank is that all you need is a battery monitor that can control a relay to open or close the charge current, instead of a dedicated DC-DC charger.

Li's do well with a constant current or voltage type charge, and 14.1v is the ideal voltage to achieve a full charge. When the batteries reach 14.1v you want the relay to stop the charge AND not apply any sort of float charge.

Your 200aH should ideally be charged a 0.3C rate or 60aH, which is approximately the charge current the alternator will supply and on a consistent basis.

In order to a achieve a ~60A charge, you will need to connect the relay to alternator side cable of the chassis battery. (Not a MB Aux. battery setup circuit).


The above is from a person with 5 years of service and with a 400aH DIY bank.





.
 
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SeattleNewbie

2013 NCV3 2500 170" WB
3. Other ways to accomplish charging your house batteries? I don't know of any unless you want to include solar or shore power as potential options.
You can power a pure sine inverter from the vehicle 12 volt system. Use the 120 volt AC output to power a shore power charger. That way you can get a proper 3 stage charge profile.

https://www.ortontransit.info/electrical
Gasp! That's a brilliant alternative! Thank you for your suggestion Dave :cheers:

I already have a charger in my inverter/charger combo, so presumably I'll only need a second inverter to connect to the Sprinter battery with a regular extension cord connected to its output

I'll do the math on cost and conversion efficiency tradeoffs and report back.
 
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OrioN

2008 2500 170" EXT
Gasp! That's a brilliant alternative! Thank you for your suggestion Dave :cheers:

I already have a charger in my inverter/charger combo, so presumably I'll only need a second inverter to connect to the Sprinter battery with a regular extension cord connected to its output

I'll do the math on cost and conversion efficiency tradeoffs and report back.
You will require an 1800W inverter to supply the needed 15A to the inverter/charger you already have and get a 60A Dc charge output.
 

autostaretx

Erratic Member
Good thing electrons travel at the speed of light.
They don't.

They're really really pokey. 5 millimeters per second or less in copper wire.

But (in the wire) they're like a stack of pennies in a roll ... if you push one in at one end, one pops out of the other end almost instantaneously. (but not quite).

The two refs i quickly found differ quite a bit in their speed calculations. One is a quarter of a millimeter per second, the other is 4 mm per second. (current, voltage and wire diameter affect this ... i'm not going to try to normalize the two references)

Electrons can randomly rattle around in copper at speeds closer to a million meters per second (one 300th of the speed of light), but they're constantly bashing into obstructions.

refs: http://www.mogami.com/e/puzzle/pzl-05.html
and https://www.physlink.com/education/askexperts/ae69.cfm

Just to mess with your head on a Sunday...

--dick
p.s. electromagnetic waves do travel near the speed of light in copper (0.9c) ... but, just like water at a beach, the speed of the wave coming towards you is *not* the velocity of the water that the wave (information) is passing through. Ducks floating 100 feet out are still 100 feet out after the wave has gone by.
 
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Graphite Dave

Dave Orton
Gasp! That's a brilliant alternative! Thank you for your suggestion Dave :cheers:

I already have a charger in my inverter/charger combo, so presumably I'll only need a second inverter to connect to the Sprinter battery with a regular extension cord connected to its output

I'll do the math on cost and conversion efficiency tradeoffs and report back.
Both my sold 2008 Sprinter and the 2015 Transit conversions have used the vehicle powered inverter. The advantage over a B2B is having 120 volt AC power available for multiple uses. Using a selector switch I can select either real shore power or "shore power" from the vehicle powered inverter. The second selector switch selects charging & powering the duplex plugs or heating shower water or heating air with 750 watt air heater.
 

SeattleNewbie

2013 NCV3 2500 170" WB
You will require an 1800W inverter to supply the needed 15A to the inverter/charger you already have and get a 60A Dc charge output.
That was my first reaction but then I realized that my Renogy 2000W Inverter / 50A Charger combo with an underestimated 85% efficiency would need a maximum of 6.5A AC as input.

50A DC * 12V = 600W
600W / 0.85 = 706W
706W / 110V = 6.5A AC

So presumably a 750-1000 Watt inverter powered by the vehicle alternator would do the job of providing the needed input to the charger. 1000 Watt pure sine Renogy inverters seem to be priced about $160. The 40A DC B2B charger is also around the same price.

The trade-offs that I like about this approach:
- "2. The house 12 volt system can be completely separate from the vehicle 12 volt system. House system can not affect the vehicle electrical system. House system is not grounded to the chassis." (mentioned in https://www.ortontransit.info/electrical)
- 12/3 AWG Wire for AC power going from the front cabin to the rear of the van rather than 2x2 AWG wires for DC power.
- Having a second inverter for emergency use if/when the current one should decide to retire.

Some minor negative trade offs:
- The second inverter is slightly large than the B2B charger in terms of space.
- The second inverter would ideally be placed close to the front of the cabin rather than the rear where the rest of the electrical equipment is.

Have I missed anything?
 

OrioN

2008 2500 170" EXT
That was my first reaction but then I realized that my Renogy 2000W Inverter / 50A Charger combo with an underestimated 85% efficiency would need a maximum of 6.5A AC as input.

50A DC * 12V = 600W
600W / 0.85 = 706W
706W / 110V = 6.5A AC

So presumably a 750-1000 Watt inverter powered by the vehicle alternator would do the job of providing the needed input to the charger. 1000 Watt pure sine Renogy inverters seem to be priced about $160. The 40A DC B2B charger is also around the same price.

The trade-offs that I like about this approach:
- "2. The house 12 volt system can be completely separate from the vehicle 12 volt system. House system can not affect the vehicle electrical system. House system is not grounded to the chassis." (mentioned in https://www.ortontransit.info/electrical)
- 12/3 AWG Wire for AC power going from the front cabin to the rear of the van rather than 2x2 AWG wires for DC power.
- Having a second inverter for emergency use if/when the current one should decide to retire.

Some minor negative trade offs:
- The second inverter is slightly large than the B2B charger in terms of space.
- The second inverter would ideally be placed close to the front of the cabin rather than the rear where the rest of the electrical equipment is.

Have I missed anything?
Your math is on the 'weak' side.

50A DC x 14.2V = 710W

The AC-DC efficiency coefficient is lower than 0.85 and I'd use 0.7 for 1000W.

You will need 8.5A Ac to drive your inv/chgr.

This 8.5A is 1000W, so your require and inverter size of 1000W x 1.15 or 1200W MIN. to be sure that things don't go sideways when things get hot.
 

SeattleNewbie

2013 NCV3 2500 170" WB
Your math is on the 'weak' side.

50A DC x 14.2V = 710W

The AC-DC efficiency coefficient is lower than 0.85 and I'd use 0.7 for 1000W.

You will need 8.5A Ac to drive your inv/chgr.

This 8.5A is 1000W, so your require and inverter size of 1000W x 1.15 or 1200W MIN. to be sure that things don't go sideways when things get hot.
Thanks for your comment. A larger margin of safety is usually better :cheers:
 

SeattleNewbie

2013 NCV3 2500 170" WB
The inverter will also last longer if it runs cooler. The LiFePO4's 's will drive this system at full charge rate for over 80% of the charging time.
That's good to know. I have noticed that my current charger will run all of its fans at full speed when the charging rate is turned up to 50A.

I suppose I should dust off the old KillAWatt and see what the conversion (in)efficiency actually is.
 

Graphite Dave

Dave Orton
Your math is on the 'weak' side.

50A DC x 14.2V = 710W

The AC-DC efficiency coefficient is lower than 0.85 and I'd use 0.7 for 1000W.

You will need 8.5A Ac to drive your inv/chgr.

This 8.5A is 1000W, so your require and inverter size of 1000W x 1.15 or 1200W MIN. to be sure that things don't go sideways when things get hot.
My Magnum 1000 watt house inverter/charger/transfer switch has a charger rated at 50 amps. I program it to charge at 40 amps. Works fine with a 1000 watt vehicle powered inverter. The vehicle powered inverter is my backup method of charging if weather conditions prevent the solar output. Solar is the primary method of charging and the backup is seldom required.
 

SeattleNewbie

2013 NCV3 2500 170" WB
That's good to know. I have noticed that my current charger will run all of its fans at full speed when the charging rate is turned up to 50A.

I suppose I should dust off the old KillAWatt and see what the conversion (in)efficiency actually is.
I got a KillAWatt and measured the AC wattage drawn by the Renogy 2000 watt inverter / 50 A charger.

The results are worse than the 70% efficiency assumption we used above:

To charge at 10 A DC drew 280 watt or equivalent of 20 A @ 13.5 v (50% efficiency)
To charge at 20 A DC drew 480 watt or equivalent of 35 @ 13.5 v (57% efficiency)
To charge at 30 A DC drew 670 watt or equivalent of 49 @ 13.5 v (61% efficiency)
To charge at 40 A DC drew 870 watt or equivalent of 64 @ 13.5 v (62% efficiency)
To charge at 50 A DC drew 1150 watt or equivalent of 85 @ 13.5 v (59% efficiency)

Sharing this so smarter folks can let me know if I've missed something and so that other readers can plan accordingly.

I got the new inverter today and look forward to figuring out how to connect it to the mystery box under the driver seat.
 

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