23 replies to this topic

[Vic Harder]

Rover John
I think the alternator was overheating due to load. I think the test was set up to see what would happen to the alternator when battery was in a discharged state hence no controller.
BMS internal protecting battery. ( I’m thinking about the internal battery BMS)
Am I wrong, I thought you could put a lot of current into a discharged battery.

Thanks Russ

You can put a lot of current into a discharged battery.  Hence the danger to the alternator.  From the Rolls Battery (AGM) manual:

 

"The recommended charge current is 10%-20% of the AH capacity of the battery bank, based on the 20 Hr AH rate (C20). Higher current levels may cause the battery bank to overheat. A lower current may be used; however, this will prolong charge time and increase the potential for sulfation build-up."

 

10% of the 250AH battery bank I had before is 25A.  Because of the internal resistance of AGM (all lead acid actually) I would see an in-rush of 90A and then it would quickly scale back to 40 and then continually decrease as the battery charged up.

 

With Lithium batteries, there is negligible internal resistance, so they will charge to full at whatever you can throw at them.  However, the maximum recharge rate is 1C (or 100 Amps for a 100-Ahr battery), and a recommended max of 0.5C for battery longevity.

 

So my battery bank in the camper (2 100AH Battleborns) will gladly accept 200A... is that smoke I see?    

[CougarCouple]

Thank you Vic for that information.
New Question.

So if there had been a change controller would that have helped? I thought those only regulated the solar. I’m pretty sure the batteries in our camper are direct from the alternator with only a fuse and the isolator to keep camper from draining the starting battery.

My brain hurts. 🥴

Russ

[Old Crow]

Very interesting video.  To me it suggests anyone who has switched over to a LiFePO4 and charges it from their truck may want to measure alternator temperatures under several scenarios (normal and stress conditions) to see if there may be an issue on that specific setup.

 

I'd think a simple $25 infrared non-contact temperature gun would do it-- no need for the FLIR thermal camera in the video.

 

This isn't the best time of year for it but doing it now or early in the season would provide baseline numbers for testing again in warmer and then very hot weather.

 

In the meantime, find operating specs for the alternator .   The video used a Balmar alternator for part of the test and Balmar is good at specs. I picked one of theirs just looking for a general idea of range and see the specs show a normal operating temperature of 180*F and max of 225*F. 

 

The other thing to do in the meantime is to seek out more info on this topic.

 

I just did a search on the Battle Born site and on this page see these comments from Battle Born staff.  They refer to a Precision Circuits Li BIM device included in the package they're selling.

 

"1. The Li-Bim is used when you are charging your batteries off of the alternator. We usually suggest using this device when you have 3 or more batteries charging off of the alternator. Because lithium batteries can take a lot of power they will try and pull as much power off of your alternator as possible which could cause your alternator to overheat. This device is specifically made for lithium batteries and will prevent your alternator from overheating. It works on a duty cycle so it will charge the batteries for 15 minutes then take 20 minutes off. It is used for 2 batteries as well depending on the amperage your alternator is outing out. If your alternator is producing around 100 amps when charging the batteries this is a good device to use. If it’s producing a lot more, say 120 amps then you might want to look into a battery to battery charger that limits the current."

.

[Atlin]

Although expensive, I bought a Redarc DC-DC charger that handles both solar and alternator inputs.  Mine limits the input to 60A.  Haven't actually tried it yet, still getting installed.

[Vic Harder]

Two comments i've seen recently.... 

1) Above "We usually suggest using this device when you have 3 or more batteries charging off of the alternator."

2) From the Sprinter forum "I haven't heard of any alternators failing"

 

I'm guessing that maybe we (I am anyway) over reacting?  Maybe there is no real threat in most situations?

 

When I put the camper back on the truck after my build up this year, I will make sure they are fairly discharged and let the truck idle for a bit and see what the temps are like

[Stokeme]

I’m looking to learn about functional (with my intermediate understanding) charging options, preferably at lower $$.

Edited by Stokeme, 08 February 2020 - 07:02 AM.

[Vic Harder]

A while back rando posted a way to inexpensively do this

http://www.wanderthe...c-dc-cheap-b2b/

[rando]

While the video is illustrative, I am not sure their test setup is really representative of the situation in a camper.  As others pointed out, that alternator is running screaming fast and only has ~2-3' of fairly beefy wire between the alternator and battery.    In our situations you typically have 20-30' of wire (10 AWG with the factory install) and the resistance in these wires is more than enough to limit the current from the alternator to the battery.   On my Tacoma I have upgraded the wire to 6AWG and still was only seeing 10A to the LiFePO4 battery. 

 

I guess this would be another case of wait to see if you really have a problem before worrying about it.   If you see that your battery is charging at 50+ Amps, then maybe you need to address it (either a DC-DC or skinnier wire).   But more likely is the case that your battery doesn't see enough current and you will want to boost it with a DC-DC. 

 

The take home from this is more - get a battery monitor - so you know what is going on and IF you have a problem. 

[smlobx]

Very timely topic.

i have one 100AH Battleborn battery in my camper and am in the process of upgrading the wire from the alternator to the plug in the truck bed. The company who did the original install ran the wire from the front of the 8 ft. Bed back to where the 7 pin pug is at the bumper and then of course it runs back up, through a crew cab and finally to the alternator.

 

I am planning on running 8AWG wire directly from the front of the truck bed to the alternator. Hopefully the distance, which is still considerable will help restrict the amperage going to the battery.

 

Another question should I install a fuse along the way....?

[Vic Harder]

Very timely topic.

i have one 100AH Battleborn battery in my camper and am in the process of upgrading the wire from the alternator to the plug in the truck bed. The company who did the original install ran the wire from the front of the 8 ft. Bed back to where the 7 pin pug is at the bumper and then of course it runs back up, through a crew cab and finally to the alternator.

 

I am planning on running 8AWG wire directly from the front of the truck bed to the alternator. Hopefully the distance, which is still considerable will help restrict the amperage going to the battery.

 

Another question should I install a fuse along the way....?

Along the way?  As in half way down the wires?  Nope.  One at each end, as close to the respective batteries as possible