RV News RVBusiness 2021 Top 10 RVs of the Year, plus 56 additional debuts and must-see units → ×


Reply
 
Thread Tools Display Modes
Old 11-29-2020, 07:11 PM   #1
Junior Member
 
Join Date: Sep 2020
Posts: 26
E450 155A alternator for charging 2 LiFePo4 batteries

I was wondering if anyone had real world experience charging 2 LiFePo4 batteries (Renogy Smart Lithium 100Ah), using a 155A alternator while driving?

I just ordered a DC amp clamp to do some testing but in the meantime, I'd like to hear about anyone who has gone this route (vs DC to DC). The specs of the batteries mention a max charge current of 50A. Set up in parallel, does that mean the maximum charge current, if they were completely empty, could be as high as 100A?

Would having a bigger alternator be a good idea (even required?) or if the current 155A one would be enough?
lduchesne is offline   Reply With Quote
Old 11-29-2020, 09:12 PM   #2
Member
 
Join Date: Mar 2018
Posts: 82
TitanMike has some experience on that, I'm sure he will chime in. But I will say that the DC-DC charger will limit the current depending on the model you buy. So I don't think the 155 amp alternator will be taxed at all.
__________________
Northern Indiana
2018 Salem Cruise Lite M-241QBXL
2018 GMC Canyon Denali
Rick the Rocket is offline   Reply With Quote
Old 11-29-2020, 09:28 PM   #3
Junior Member
 
Join Date: Sep 2020
Posts: 26
Quote:
Originally Posted by Rick the Rocket View Post
TitanMike has some experience on that, I'm sure he will chime in. But I will say that the DC-DC charger will limit the current depending on the model you buy. So I don't think the 155 amp alternator will be taxed at all.
I was actually looking at _not_ installing a DC to DC charger and just let the batteries pull whatever they can
I'm curious what TitanMike think about this plan. But again, I don't mind going to the Ford Truck center and have a really big alternator installed. I just don't want to do it if it's not necessary.
lduchesne is offline   Reply With Quote
Old 11-29-2020, 10:17 PM   #4
Senior Member
 
Join Date: Jul 2017
Location: North of Seattle, WA
Posts: 10,292
Just some things to consider.
Lithium batteries will draw all the power you can throw at them from an alternator limited only to the voltage drop due to wire size and distance. That can be bad, very bad actually, if the current exceeds .5 C which would be 100 amps for 2 LiFePo4 batteries in parallel.
Of course factory wiring won't carry enough current without large voltage drops so damage probably won't occur unless larger wire is installed.

Second issue. Alternator regulated voltage won't provide more than around 90% SOC and also won't provide cell balancing.

Next, some form of isolation neexs to be provided or starting battery will draw down house batteries when engine is off.

Lastly, price out a large alternator then price out a DC-DC charger. The charger will run $130-$200 and a high output alternator up to 3X that. The DC-DC charger will also act as an isolator so when ignition is turned off batteries are isolated.

There's more but this covers the major issues.

The nice thing about a DC-DC charger is that it can be tailored for a LiFePo4 battery' desired charging profile without altering the desired charge profile for the lead acid starting battery.
__________________
"A wise man can change his mind. A fool never will."

"You only grow old when you run out of new things to do"

2018 Flagstaff Micro Lite 25BDS
2004 Nissan Titan
TitanMike is offline   Reply With Quote
Old 11-29-2020, 11:26 PM   #5
Junior Member
 
Join Date: Sep 2020
Posts: 26
Quote:
Originally Posted by TitanMike View Post
Lastly, price out a large alternator then price out a DC-DC charger. The charger will run $130-$200 and a high output alternator up to 3X that. The DC-DC charger will also act as an isolator so when ignition is turned off batteries are isolated.
Yes that's very true especially that I would not be installing it myself. I just finished installing this Li BIM-225 to replace the original solenoid and was hoping to not have to change it right away.

Looking at how a DC to DC is installed, it looks like I need both negative wires in there, which is something I don't have right now. On the house battery side, it goes directly to the chassis so it seems easy. On the chassis battery side, do you know if there's any way to avoid running a cable all the way to the battery-?

It's not clear to me, looking at the wiring diagrams for my RV, where that negative terminal ends up.
lduchesne is offline   Reply With Quote
Old 11-29-2020, 11:35 PM   #6
Junior Member
 
Join Date: Sep 2020
Posts: 26
There's also two thing I notice I would lose: the easy setup of for momentary switch for boosting my chassis battery in case it is too low and the ability to charge the chassis battery, again if too low, when plugged into shore power (or when the house battery is charged enough).
lduchesne is offline   Reply With Quote
Old 11-29-2020, 11:41 PM   #7
2012 Solera
 
Join Date: May 2012
Posts: 1,516
On my MBS, the chassis and house grounds - negatives - are common. Don’t think using both the LiBIM and a dc-to-dc is going to work. When the BIM relay closes connecting the chassis and house batteries in parallel, it will short the input to the output of the dc-to-dc converter.
__________________
JLeising
2012 Solera "S"
Calif SF Bay Area
JLeising is offline   Reply With Quote
Old 11-30-2020, 12:59 AM   #8
Junior Member
 
Join Date: Sep 2020
Posts: 26
Quote:
Originally Posted by JLeising View Post
On my MBS, the chassis and house grounds - negatives - are common. Donít think using both the LiBIM and a dc-to-dc is going to work. When the BIM relay closes connecting the chassis and house batteries in parallel, it will short the input to the output of the dc-to-dc converter.
I was kind of thinking of doing that, both LiBIM and DC to DC converter, but I guess that's not going to work.

So in your case, you would just wire both negative from the charger together to the same point on your chassis? Just thinking about that, my simplistic view of electrical systems breaks down completely
lduchesne is offline   Reply With Quote
Old 11-30-2020, 03:20 AM   #9
2012 Solera
 
Join Date: May 2012
Posts: 1,516
Quote:
Originally Posted by lduchesne View Post
I was kind of thinking of doing that, both LiBIM and DC to DC converter, but I guess that's not going to work.

So in your case, you would just wire both negative from the charger together to the same point on your chassis? Just thinking about that, my simplistic view of electrical systems breaks down completly
Yes - that is what I did after I disabled the battery interconnect relay by disconnecting the coil primary wire (my 2012 didnít have a BIM as such, but had a battery control center with a battery interconnect relay).
__________________
JLeising
2012 Solera "S"
Calif SF Bay Area
JLeising is offline   Reply With Quote
Old 11-30-2020, 02:44 PM   #10
Senior Member
 
Join Date: Jul 2017
Location: North of Seattle, WA
Posts: 10,292
This "conversation" is pointing out the major difficulties in mixing battery chemistries, LiFePo4 and Lead/Acid and trying to use the same charging system.

The LiBIM is a compromise at best which merely tries to decide which battery needs charging and in order to prevent overcharging of one or the other by switching on the charge intermittently.

If a Lithium battery bank is almost totally discharged to 10% SOC, on a 200 amp bank that means 180 amp hours needs to be replaced. If the starting (coach) battery started the engine quickly that means it will be fully charged in short order and charging voltage from alternator will drop to ~13.6-13.8 volts. How much charging current will the LiFePo4 batteries receive under this condition? For the sake of discussion let's say 50 amps. If the LiBIM is switching on charging current for 20 minutes or so then off for 30 minutes that means that the LiFePo4 batteries are only receiving 25 amp hours of charging current. Our hypothetical battery bank is going to take 7.2 hours to charge under that scenario.

With a DC-DC charger capable of delivering 40 amp rate (Like a Renogy DCC 1212-40) that same battery bank under same conditions will only take 4.5 hours.

If one leaves a campsite and drives to the next which is more likely, a 4.5-5 hour trip--------or a 7.5-8 hour trip.

Yes, all the obstacles of inability to use the "Dead Battery Start" and charging of coach battery on shore power are there without the LiBIM but not insurmountable.

The Battery interconnect switch for a boost start is as simple as using a Relay controlled by a SPDT switch. Using the normally closed contact it sends the control signal to the DC-DC charger which keeps it active whenever the ignition switch is on and engine running. When the switch is activated for a "boost" the Ignition signal is then changed to the other contact which then activates the interconnect relay ad the DC-DC charger is no longer active, isolating the batteries from the system and re-routing their connection through the relay. No Shorts, back-feeding, etc. Release switch/button and all is back to charging the house batteries.

As far as keeping the coach battery charged while on shore power, a simple battery minder left plugged into a nearby house AC receptacle and permanently connected to the coach battery will definitely lessen the possibility of the coach battery going dead while shore power (or generator power) is available. Will also work whenever an inverter is on and powering outlets but power draw on most maintainers is nominal, especially if the battery is not discharged. They're maintainers and often don't draw more than 20 watts (~ 2 amps of inverter input which drops to milliamps when the "maintained" battery is full.)

I don't have a motorhome but the only difference is the distance from alternator to batteries and how I connect the two.

A BIM is a good idea as long as battery chemistry is identical. With Lithium it's at best a poor compromise if one wants full batteries when they arrive at their boondocking location. As with all compromises, something is given up in order to "make the deal".

I'd rather (and have) built two different systems where the starting battery is maintained the way the charging system was designed and the LiFePo4 batteries are maintained the way they need to be, including cell balance with the higher voltage.

That's how I see it based on how the makers of the LiBIM describe their product and watching the actual voltages available on my charging system. I do see 14.7 volts when I start the engine and drive for a few miles but once the starting battery is fully charged the voltage drops to 13.6-13.8 which will charge a LiFePo4 battery but unfortunately not fully and it won't provide any cell balance which is essential when the batteries are Deep Cycled.

I'm open to discussion on this and if I'm wrong, please feel free to point out where. I may be old but I learn new things every day.
__________________
"A wise man can change his mind. A fool never will."

"You only grow old when you run out of new things to do"

2018 Flagstaff Micro Lite 25BDS
2004 Nissan Titan
TitanMike is offline   Reply With Quote
Old 11-30-2020, 08:29 PM   #11
Junior Member
 
Join Date: Sep 2020
Posts: 26
Thanks TitanMike for taking the time to write this up. I agree the downsides (which can be worked around, as you said) are probably not worth taking on the risk of burning a big piece of equipment.

Ultimately, my personal use case is that I'll be installing 600W of solar panels within the next year, and that we're always camping in or around California. That means in the end, that this charging capacity will not be used much.

You convinced me to go DC to DC just for the safety/peace of mind of it. Looking at various models, I think I prefer the Victron Smart 12/12, which they only do in 30A as far as I can see. It would be marginally better than the LiBIM for charging time, but would do it safely.
lduchesne is offline   Reply With Quote
Old 12-03-2020, 02:50 PM   #12
Senior Member
 
Tom48's Avatar
 
Join Date: Apr 2015
Location: Ontario, California
Posts: 1,613
That all gets pretty deep but especially Titan Mike's stuff is good. For my part I understand that a hungry LiFePo will have demand that may exceed the wiring, BUT WILL surely exceed the duty cycle of the alternator and fry the alternator or the wiring or Both


Good Luck
__________________
Tom48
In Sunny So Cal /w
Now in 2005 Holiday Rambler Ambassador DP and The Hot Air Balloon RESTLESS
NO MORE Tricked out
2017 Sandstorm 250 T.H.
Tom48 is offline   Reply With Quote
Reply

Tags
batteries, charging

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by Forest River, Inc. or any of its affiliates. This is an independent, unofficial site.



All times are GMT -5. The time now is 08:26 PM.