Alternator charging above 50 amps

[Sipma02]

Hello all! I've been snooping around here for the past few weeks, and have all my questions answered by searching and just reading and researching. There is such a wealth of knowledge, it's incredible!

I'm currently working on building out a 2006 Sprinter (you can see details here: https://www.facebook.com/groups/573929156547519) and I've come across LiFePo4 batteries and being pretty much ideal for a house/leisure battery setup.

I've done a fair amount of research, and there are a staggering amount of options. I know I want a pretty big battery bank, and I plan on getting 4 280ah 3.2v Xuba Lifepo4 batteries and wiring them in series for a 12.8v pack. There's a strong possibility that I would add another 4 3.2v 150ah or possibly even another 4 3.2v 280ah down the road. Our daily predicted energy usage is around 1Kw, and we want to be able to be offgrid for 3-5 days. I'll for sure be running a BMS, probably a Choice BMS or Electrodacus.

My roof setup pretty much dictates that I stick with 450 watts of solar, split between 3 150 watt panels. By my calculations, this isn't really going to be enough solar. It will help extend our time between drives though. We want as much flexibility as possible. Since we'll be full time in the van, we'll probably be driving pretty frequently. The van has a 150 amp alternator, and after standard vehicle loads, I can draw about 80-100 amps from the alternator. Estimating conservatively, 60-80 amps. I'd like a DC DC charger capable of charging the 280ah (and potentially larger in the future!) pack as fast as possible/least drive time possible.

The Xuba cells are rated for at least a .5C charge rate, and .5C with a 280ah pack is 140 amps! So the fastest I can really charge is around .3C or so (~80amps from the alternator)

The main problem I'm running into is all the DC DC chargers rated for 50+ amps are very expensive. I currently have my eye on the Kisae DMT1250, which will provide 50amps of alternator and solar input. If I go with the Electrodacus, it has a built-in solar controller, but isn't the most efficient (PWM vs MPPT) but I've read that might not be as big of an issue as I think. I would still need a large/expensive DC DC charger...

• Can I wire 2 DC DC chargers in parallel?
• Something alternative to a DC DC charger? (just confirming... I do need a DC DC charger, correct? The BMS does not take place of a DC DC charger, right?)
• Is there any BMS options with a build in charger?
• Could I parallel a set of these instead of a DC DC charger? https://usa.banggood.com/1200W1800W...c-Vehicle-Booster-p-1599490.html?rmmds=search
• Are there any other options I have?

...Hoping for some wisdom here! As you can see, I know enough to be dangerous... or maybe not. Ha. Thanks so much

 

[Electric Personality]

I predict a very short alternator life if you suck that much current out of it. You need to know rpm required for continuous output, and what continuous is. 50 amps from a dc to dc charger is likely to be 65 or so from alternator. My truck has a 220 amp alternator, and I only want to tap it for 40 at the output so maybe 50 input. Anyway, I am sure it will get hot.....

 

[Sipma02]

I predict a very short alternator life if you suck that much current out of it. You need to know rpm required for continuous output, and what continuous is. 50 amps from a dc to dc charger is likely to be 65 or so from alternator. My truck has a 220 amp alternator, and I only want to tap it for 40 at the output so maybe 50 input. Anyway, I am sure it will get hot.....

I will double check my numbers. I know other T1N (2002-2006) Sprinter owners have pulled as much from their vans without problem. The van is stock with a 120amp alternator (edit: actually 90a stock!), so the 150a is an upgrade. Its actually possible to go further to a 200amp alternator, maybe someday.

Thanks for the input!

 

[mapguy525]

The issue is not the amount of output available from the alternator. It is where in the RPM range the output is located. Need a output graph to review the Alternators output as built.

The real issues are heat and duty cycle -especially with LFP batteries being charged. If discharged much these batteries will accept all the output of the alternator. Effectively this puts nearly 100% duty load on the alternator which most are not designed for. Lead acid and AGM batteries are not as efficient at charging -so you don't see many over-production based failures of the alternator like seen with LFP.

 

[boondox]

I pull 50 amps from a 150 amp alt on my Transit. As noted above, you will pull around 60-65 amps to charge at 50 amps. I can tell you that at idle the alt gets hot! On the road it does better. Remember that your alt is doing more than charging your house battery. You might look into a second alternator.

 

[mapguy525]

I pull 50 amps from a 150 amp alt on my Transit. As noted above, you will pull around 60-65 amps to charge at 50 amps. I can tell you that at idle the alt gets hot! On the road it does better. Remember that your alt is doing more than charging your house battery. You might look into a second alternator.

What range of temps are you seeing with the alternator. Depending on temps - external regulation could help the long term reliability of the system by keeping the diodes and control circuits in the proper operating temp range.

 

[boondox]

What range of temps are you seeing with the alternator. Depending on temps - external regulation could help the long term reliability of the system by keeping the diodes and control circuits in the proper operating temp range.

I don't know the actual temperature. I have a lot of experience pulling maximum power from alternators so I can tell that running it at idle is pushing it and limit it to 20-30 minutes, after which the alt is hot but not critical. I could break out my non contact thermometer but I don't think reading the outer case means all that much. With most modern vehicles I don't think you can do external regulation, if you mean control the field coil, unless you install a second alt. In my case if I do end up hurting the alternator's feelings too badly I'll upgrade to a 200 amp alt. Although improving the cooling at idle would be another solution and I have done that before but it is so hard to work on a van under the hood that just getting a larger alt would be easier.

 

[mapguy525]

I speak about the long term reliability because I know how difficult alternator replacements are on Moho's and vans of all kinds. Considering that Murphy's Law will have the failure happen 40 miles from Stanley, Idaho at the end of a narrow two track...….prompts me to weigh all the plus and minus of the installed system.

Check out the link. They are on ebay too.
https://alternatorparts.com/quicktifier-external-bridge-rectifier.html

 

[Sipma02]

The issue is not the amount of output available from the alternator. It is where in the RPM range the output is located. Need a output graph to review the Alternators output as built.

The real issues are heat and duty cycle -especially with LFP batteries being charged. If discharged much these batteries will accept all the output of the alternator. Effectively this puts nearly 100% duty load on the alternator which most are not designed for. Lead acid and AGM batteries are not as efficient at charging -so you don't see many over-production based failures of the alternator like seen with LFP.

Interesting. That is good to know. What exactly does "discharged much" mean? There is always the chance we'd be boondocking for 3-4 days, with nearly dead batteries. I think I feel good about pulling 60-70 amps from the upgraded alternator – I'll def watch temps though.

I speak about the long term reliability because I know how difficult alternator replacements are on Moho's and vans of all kinds. Considering that Murphy's Law will have the failure happen 40 miles from Stanley, Idaho at the end of a narrow two track...….prompts me to weigh all the plus and minus of the installed system.

Check out the link. They are on ebay too.
https://alternatorparts.com/quicktifier-external-bridge-rectifier.html

This is super awesome! It's a big block of text. I read/skimmed most of it. What exactly does it do? Convert AC (from alternator) to DC? Normally an alternator does that internally, correct? So this basically externalises the AC to DC conversion which makes the alternator run cooler?

 

[boondox]

Map, do you have any idea if these will work on a late model vehicle? I would suspect not in the case of my Transit and I don't even have the "smart" alternator. I would consult the equivalent of the Body and Equipment Mounting Manual for your Sprinter.

 

[mapguy525]

Contact the people on the webpage. They have been helpful in the past tailoring equipment to application.

 

[mapguy525]

Interesting. That is good to know. What exactly does "discharged much" mean?

___SNIP__

Situation where you start engine and the alternator is charging 100% capacity for a lengthy time due to depleted batteries. Understanding the charge and discharge characteristics of LFP batteries compared to Lead Acid/AGM is important here.

 

[Sipma02]

Situation where you start engine and the alternator is charging 100% capacity for a lengthy time due to depleted batteries. Understanding the charge and discharge characteristics of LFP batteries compared to Lead Acid/AGM is important here.

Makes sense. I've got a fairly firm grasp of C ratings when it comes to charging/discharging. Where can I read up about any more differences?

 

[mapguy525]

Marine based system info:
https://marinehowto.com/lifepo4-batteries-on-boats/

http://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/

280a prismatic cell specs here:
https://diysolarforum.com/resources...-product-specification-version-e-2019-7-5.15/

 

[Sipma02]

Wow. Been reading a lot the past few days. Thanks! Really appreciate those links!