Using alternator for 48v battery bank

[f-stopLuke]

Hey folks,

I’m currently designing a 48v system using the following components...

(4) LG Neon 350 watt panels : https://tandem-solar-systems.com/buy-solar-products/lg350n1c-v5-neon-2-blkwht-module/

MPP 3048LV-MK 3000 watt, 48v inverter/charger : http://www.mppsolar.com/v3/catalogs/PIP-LV-MK.pdf

(2) 24v 200ah lithium batteries wired in series : Lifepo4 100ah 200ah 300ah 400ah 24V Lithium ion Battery for Solar System/Motor Home/Boat/Golf Carts car battery (24V 200ah ×1pcs) https://www.amazon.com/dp/B07TWCQRBK/ref=cm_sw_r_cp_tai_qNDTEbXNK45ZM

The next concern I’m trying to address is the ability to charge my 48v battery bank using the alternator. I’ve done a little looking around and I have found this Sterling 12v - 48v dc-dc charger : https://www.sterling-power-usa.com/SterlingPower12volt-to-48volt-batterytobatterycharger.aspx

My first concern is that I have a 120 amp alternator, and this is the only 12v to 48v b2b charger that I have been able to find, but it’s only rated for 70a input. My question for this concern is.. Will this still work? Or will it totally fry the b2b charger? Do I need to find this same type of component but one that is rated for 120+ amps? If so, does anyone have a link to one? Or is there perhaps some other workaround for this?

My second concern is how to go about wiring it into the solar charging system. I’ve looked around a bit and seen some designs that use a relay system. Does anyone know of one that would work for this application? Has anyone done this or tried this before?

Any useful information regarding this setup would be greatly appreciated. I’m aware I could probably solve this issue on my own with a little deeper research but I’ve kind of run out of steam searching threads and forums.

 

[dgjonesy]

So the Sterling DC-DC charger could suck up to 70 A from your 120 A alternator which I think could stress your alternator if done for long periods of time with other high vehicle loads.

I’ve attached a Victron doc which shows a system similar to yours, except with Victron products of course. But the point is they tie the inverter/charger and DC-DC charger together to the battery. I think you should be able to do something similar.

 

[f-stopLuke]

So the Sterling DC-DC charger could suck up to 70 A from your 120 A alternator which I think could stress your alternator if done for long periods of time with other high vehicle loads.

I’ve attached a Victron doc which shows a system similar to yours, except with Victron products of course. But the point is they tie the inverter/charger and DC-DC charger together to the battery. I think you should be able to do something similar.

thank you for the reply! So if I’m understanding you correctly.. you’re saying the amperage rating is for how many amps it will actually push to the battery? Because I was under the impression that the charger had to be rated for the same amperage of the alternator. And I couldn’t find anything like that on the market.

My next question then is, how do you know how much amperage you can ‘steal’ from the alternator? Is there any kind of existing formula??

 

[dgjonesy]

thank you for the reply! So if I’m understanding you correctly.. you’re saying the amperage rating is for how many amps it will actually push to the battery? Because I was under the impression that the charger had to be rated for the same amperage of the alternator. And I couldn’t find anything like that on the market.

My next question then is, how do you know how much amperage you can ‘steal’ from the alternator? Is there any kind of existing formula??

Yeah so the spec sheet on the Sterling charger says that at 12V in and 48V out the “Amps in” is 70A. So assuming 90% efficiency the current output at 48V would be

.9 * 12/48 * 70A = 15.75 A

 

[mikeb]

why couldn't you input your alternator 14v output to the D.C. input to the MPP inverter/charger and let it charge the bateries? i believe even if you had to disconnect you solar panels while doing this it could be done.

 

[dgjonesy]

why couldn't you input your alternator 14v output to the D.C. input to the MPP inverter/charger and let it charge the bateries? i believe even if you had to disconnect you solar panels while doing this it could be done.

MPPT controllers usually require input voltage to be at least 5 volts greater than output voltage

 

[mapguy525]

On the alternator charging.
The alternator needs protection against:
Heat
Duty Cycle
abrupt load dump

The challenges of alternator charging are discussed very well on the Marine How To website:
https://marinehowto.com/lifepo4-batteries-on-boats/

Search on "Alternator Protection Devices". This will get you directly to solutions, but to understand the full implications of multiple charge sources read and analysis the whole article.

This website is a very good reference on implementation challenges of LFP installs that have multiple charge sources.

 

[dgjonesy]

So on reading the Sterling charger spec sheet more closely I see this :

6) Night Time Setting: Allows the unit to ran at half the power so the fan noise is kept down.

So supplying 35A might be doable for your alternator without too much stress

 

[f-stopLuke]

You can "steal" it all . As long as everything is off and the engine is running. But like he said above, your putting extra wear on your alternator, and avoid doing it if the heater, headlights, or wipers have to be on too. I've been playing with electrolysis on my truck, and taking every bit of amprage to make hydrogen gas. Its just like turning everything on at the same time on high

Ah okay okay, do you happen to know at what point I would be putting any kind of ‘stress’ on the alternator? I certainly would want to avoid damaging it or having to replace sooner than expected. I would even be interested in eventually installing the 220 amp alternator option but for now I wanna be able to get on the road by mid-July. Once again, I very much appreciate the responses!

 

[f-stopLuke]

On the alternator charging.
The alternator needs protection against:
Heat
Duty Cycle
abrupt load dump

The challenges of alternator charging are discussed very well on the Marine How To website:
https://marinehowto.com/lifepo4-batteries-on-boats/

Search on "Alternator Protection Devices". This will get you directly to solutions, but to understand the full implications of multiple charge sources read and analysis the whole article.

This website is a very good reference on implementation challenges of LFP installs that have multiple charge sources.

Very good information! Thank you for the source, I’ll be keeping this all in mind as I continue the design

 

[f-stopLuke]

So on reading the Sterling charger spec sheet more closely I see this :

6) Night Time Setting: Allows the unit to ran at half the power so the fan noise is kept down.

So supplying 35A might be doable for your alternator without too much stress

Y’know when I first read that I figured “why would I need that” and just kinda forgot about it. But you bring up a very good point! Thank you for that reminder as that’ll probably come in handy

 

[f-stopLuke]

I feel like I’ve gotten a good bit of information about using the alternator. But I’m still concerned about the idea of hooking the DC-DC charger directly to the positive bus bar that would be connected to my battery and the MPPT/inverter/charger.

Does anyone know if charging the batteries from the alternator AND the MPPT at the same time would be problematic?

Then my next question is a basic one about gauging your battery cables..

Should I be gauging the battery cable (and fuses) for both the charging current AND the load currents? Let’s just say I’m charging at 80 amps and I’m using 80... Do I need 80 (100) amp rated cable or 160 (200) amp rated cable? Or does the charge current sort of just supply the load current directly at the bus bar?

 

[dgjonesy]

I feel like I’ve gotten a good bit of information about using the alternator. But I’m still concerned about the idea of hooking the DC-DC charger directly to the positive bus bar that would be connected to my battery and the MPPT/inverter/charger.

Does anyone know if charging the batteries from the alternator AND the MPPT at the same time would be problematic?

Then my next question is a basic one about gauging your battery cables..

Should I be gauging the battery cable (and fuses) for both the charging current AND the load currents? Let’s just say I’m charging at 80 amps and I’m using 80... Do I need 80 (100) amp rated cable or 160 (200) amp rated cable? Or does the charge current sort of just supply the load current directly at the bus bar?

Should be fine connecting DC-DC charger and MPPT together to battery busbar (see this and Victron system diagram above) even if they have diff charge profiles. Make sure your battery can handle combined current of MPPT and DCDC charger.

Currrents are additive so if you are charging at 80 A and using 80 A the battery will need to supply zero current. So your battery cable gauge needs to be sized for max of max load current or max charging current.

 

[f-stopLuke]

Should be fine connecting DC-DC charger and MPPT together to battery busbar (see this and Victron system diagram above) even if they have diff charge profiles. Make sure your battery can handle combined current of MPPT and DCDC charger.

Currrents are additive so if you are charging at 80 A and using 80 A the battery will need to supply zero current. So your battery cable gauge needs to be sized for max of max load current or max charging current.

wow, very helpful thread you’ve linked to. I appreciate the time taken to share resources and knowledge! I *think* this clears up the few concerns and questions that I just couldn’t seem to find on my own. thank you!

 

[f-stopLuke]

Should be fine connecting DC-DC charger and MPPT together to battery busbar (see this and Victron system diagram above) even if they have diff charge profiles. Make sure your battery can handle combined current of MPPT and DCDC charger.

Currrents are additive so if you are charging at 80 A and using 80 A the battery will need to supply zero current. So your battery cable gauge needs to be sized for max of max load current or max charging current.

wow, very helpful thread you’ve linked to. I appreciate the time taken to share resources and knowledge! I *think* this clears up the few concerns and questions that I just couldn’t seem to find on my own. thank you

The moment you turn your headlights on, your stressing it. The moment your flicking a toggle to activate your electrolysis , your stressing it, when you put your wipers on high, your headlights on , and the heater is maxed , your severely stressing your alt, duh.

Maybe I need to clarify what I mean by stressing.. I’m aware that putting any load on an alternator/generator makes it work harder.

What I mean by ‘stress’ is using it to the point of actually damaging it or causing it to overheat or using so much power that it can’t keep up with the current output.

For example, I work in the television industry as a lighting technician and we regularly use big generators like 1200A or 1400A plants. Sometimes smaller like 500A or even just a 60A or 20A putt putt.

Our general rule is to never use more than 80% of the generator’s capacity. So if I know we’ll be using 2 18k lights I could theoretically get away with a 500A plant but we would typically just size up to a 1200 so we don’t ‘stress’ the generator. Same goes for balancing a load in 3 phase but that’s kind of a different subject.

Anyway, I wasn’t sure if there was any specific or detailed information on choosing a size of a dc-dc charger relative to the alternator size.

 

[dgjonesy]

wow, very helpful thread you’ve linked to. I appreciate the time taken to share resources and knowledge! I *think* this clears up the few concerns and questions that I just couldn’t seem to find on my own. thank you


Maybe I need to clarify what I mean by stressing.. I’m aware that putting any load on an alternator/generator makes it work harder.

What I mean by ‘stress’ is using it to the point of actually damaging it or causing it to overheat or using so much power that it can’t keep up with the current output.

For example, I work in the television industry as a lighting technician and we regularly use big generators like 1200A or 1400A plants. Sometimes smaller like 500A or even just a 60A or 20A putt putt.

Our general rule is to never use more than 80% of the generator’s capacity. So if I know we’ll be using 2 18k lights I could theoretically get away with a 500A plant but we would typically just size up to a 1200 so we don’t ‘stress’ the generator. Same goes for balancing a load in 3 phase but that’s kind of a different subject.

Anyway, I wasn’t sure if there was any specific or detailed information on choosing a size of a dc-dc charger relative to the alternator size.

I’m not an expert on alternators but I think your experience with generators is applicable here. Running close to 100% of capacity for long periods will impact lifetime usually because of excess heating. This suggests not using more than 2/3 of your alternator capacity. So a DCDC charger load of 70A on a 120A alternator seems significant.

 

[f-stopLuke]

I hear all kinds of warnings from people, but have not noticed the impact people claim it will have. Weather its having a huge stereo amplifier that actually dims your headlights with every bass impact, or using additional fog lights . Once I did the rough math, it seems to me that the alternators have X amount of life, and that doesn't seem to change when adding new draws to it, it just uses X faster is all. I hope that makes sense, and its not scientific, just a life time of observation and I always have done my own mechanic work. Did I mention I'm very old ?

Haha well thank you for the information! It seems that the topic of electricity tends to be surrounded with fallacies and incomplete data to support certain fears.

I’m with you on just testing something out and seeing how it goes. I’ll try this alternator charger out and if my alternator dies in a few years I’ll get a nicer bigger one ?‍

 

[dgjonesy]

Haha well thank you for the information! It seems that the topic of electricity tends to be surrounded with fallacies and incomplete data to support certain fears.

I’m with you on just testing something out and seeing how it goes. I’ll try this alternator charger out and if my alternator dies in a few years I’ll get a nicer bigger one ?‍

So you might be able to avoid the expense of a new alternator by using an inexpensive thermocouple thermometer like this and monitoring alternator temps. Seems like temps over 225F could be a problem (see this )

 

[f-stopLuke]

So you might be able to avoid the expense of a new alternator by using an inexpensive thermocouple thermometer like this and monitoring alternator temps. Seems like temps over 225F could be a problem (see this )

Once again very useful information! I’ll be keeping this in mind as I move forward with installing the sterling. Perhaps I’ll go ahead and get a temp monitor and look into what kind of temp protection my stock alternator already has or if I should invest in a component/device that I could use to monitor and control that.

Just from what I’ve read so far it seems like the night time mode of 35A charge wouldn’t be much stress on the diodes, unless of course I was idoling and also running heat or something like that. I plan on trying to only run the dc-dc charger if I’m actually driving a long distance. I’m probably just going to put a switch in line so I can turn the charging on and off manually

 

[dgjonesy]

Once again very useful information! I’ll be keeping this in mind as I move forward with installing the sterling. Perhaps I’ll go ahead and get a temp monitor and look into what kind of temp protection my stock alternator already has or if I should invest in a component/device that I could use to monitor and control that.

Just from what I’ve read so far it seems like the night time mode of 35A charge wouldn’t be much stress on the diodes, unless of course I was idoling and also running heat or something like that. I plan on trying to only run the dc-dc charger if I’m actually driving a long distance. I’m probably just going to put a switch in line so I can turn the charging on and off manually

Sounds like a smart approach!