switching to lithiums and truck trickle charger

[robert135]

Hi all,

New member here.

I am switching from AGMs to lithiums in my trailer.

It occurs to me that insofar as the trickle charger from my truck (ram 5500 with cummins 6.7) is also trickle charging the trailer as I drive, and that that voltage is surely set for lead acid voltage, rather than the 14.x required to charge these lithiums, that I may need to do something about this.

My concerns are whether or not allowing the lithiums to be trick charged at much less than 14.4, could cause a problem.........or would just result in less than effective charge when taking place.

I want the lithiums enough to forego the trickle charging if I have to.

May I have your thoughts, please?

Many thanks!

robert

 

 

 

[GlennWest]

Probably be fine. Not much goes thru those small wires. If you don't want to just pull fuse on camper. 

[robert135]

thank you kindly.

[Darryl&Rita]

You need a higher voltage from the truck end to be able to "push" current into the trailer batteriies. Not enough voltage, you may see the trailer trying to charge the truck. Get a DC to DC voltage converter, or live without charging from the truck.

[jcussen]

As Darryl said, you will have to raise the voltage coming from the alternator to one suitable for lithium batteries, normally a constant voltage 14+ volts depending on battery. A dc-dc charger will do that. I use this one,  https://www.victronenergy.com/blog/2019/10/10/new-product-orion-tr-smart-dc-dc-charger/

[robert135]

i am willing to lost the trickle charge completely if that is what this takes.

i figured there was some dc to dc conversion possible, but I want to try to ascertain what that is really worth, compared to what I lose by not having the charge at all.

the only real reason is the inverter powering a residential fridge, and especially with these lithiums being able to go so deep without damaging the batteries, i am not sure...all the ore so with the solar panels on the truck doing some charging anyway.......that i am really losing anything, practically speaking.

i had not even thought about what you said about the trailer trying to charge the truck. could you please be more specific about exactly why that would happen (I am in learning mode)?

thank you.

 

[robert135]

Jcussen,

I was answering daryl, when your post came in. thank you for the link.

do you use the converter for this reason (the trickle charger)?

 

[Darryl&Rita]

5 minutes ago, robert135 said:

i had not even thought about what you said about the trailer trying to charge the truck. could you please be more specific about exactly why that would happen (I am in learning mode)?

Basically, the truck voltage regulator "may" see the higher voltage, and disconnect the alternator. Al the truck electrical will run off the trailer batteries, until the volt drop is enough to bring the alternator back online. It won't hurt anything, except run tome on the trailer bank.

[robert135]

thank u again.....

 

[jcussen]

31 minutes ago, robert135 said:

Jcussen,

I was answering daryl, when your post came in. thank you for the link.

do you use the converter for this reason (the trickle charger)?

Yes, I have a motorhome, but same situation,  lithiums take a fast charge, and the dc-dc charger will handle that, and still keep your lithium batteries charged and protect your alternator as well.

 

 

[oldjohnt]

Welcome aboard Robert, good question, here are my thoughts.

1) At best, charging any house batteries (regardless of chemistry) via the engines alternator may NOT provide the quantity and quality as a modern 3/4 Stage Smart Charger that's suited for the battery chemistry, especially if Lithium.

2) The house battery charge also depends on the size of wires used, their length, the regulation scheme of the alternator,  the state of the engine battery, and if the mixed batteries intended for charging are the same type, which they are NOT. I just don't envision good charge balance trying to charge Lithium and Lead Acid at the same time !!!!!!!!!!!!

3) If you want the trucks alternator to provide at least some degree of charge to the house batteries (still subject to some variables)  I SUGGECT USE OF A DC TO DC CONVERTER/CHARGER suitable for the Lithium house batteries.

4) Given the expense of Lithium batteries I would NOT risk damaging them or voiding a warranty. IE charge them using a quality charger (even if DC to DC)  tailored for Lithium batteries.

NOTE Im NOT saying your idea may not provide at least "some" charging (even if not perfect or recommended) to the Lithiums, I'm ONLY saying it wouldn't be my choice for those reasons above.....

 

 John T

[GlennWest]

There is only #10 wire going thru that plug

[jcussen]

If as Glen says, you only have 10 gauge, you will not be able to supply much with a dc-dc charger, considering the length of the run from the truck to the trailer. If you don't have a residential fridge or other heavy load running all the time, I would just disconnect the trailer charging line. Make sure your converter is set up for lithium charging, so when you do plug in, it does charge properly.

[Lou Schneider]

3 hours ago, jcussen said:

If as Glen says, you only have 10 gauge, you will not be able to supply much with a dc-dc charger, considering the length of the run from the truck to the trailer. 

The Renogy DC to DC battery charger produces it's full charging current with inputs as low as 8 volts - that's a 40% voltage drop if the alternator is putting out 13.5 volts.

This makes the voltage drop loss along the charging wire irrelevant.  You'll never see that much loss unless the charging wire is running red hot and melting it's insulation.  

Edited August 23, 2020 by Lou Schneider

[GlennWest]

So you saying one can put a Dc/DC charger and charge a battery from a #10 wire. 

 

[oldjohnt]

Glenn, It depends on WHERE the DC to DC charger is located. If its right at the house batteries IE short output charge wire, that reduces output line voltage drop from charger to batteries. HOWEVER, if its located at the energy source (like near the engine alternator) and far from the house batteries, then there will be more output line voltage drop all (either end) subject to Current,,,,,,,,,,,Wire Size,,,,,,,,,,,,Length of wire.

I interpret Lou's post as saying even if there's a lot of line voltage drop from alternator to a DC to DC charger (like say it was located way back at the house batteries far from alternator OR a small wire was used) and even if its down to 8 volts, the house batteries can still get "some" charge via the DC to DC system operation.    

REGARDLESS, one should avoid line voltage drop on EITHER side of the DC DC charger, Input or Output, as that's wasted I Squared R heat energy grrrrrrrrrrrrrrr...........The more the current, the greater the distance, the smaller the wire THE GREATER THE VOLTAGE DROP on either side of the DC to DC.

i agree if the charge wire from say an engine alternator all the way back to a rear RV plug, especially if 10 Gauge wire is used, can subject to length and current, reduce the charging capacity. I'm talking about a straight battery to battery connection  here  NOT an improved DC to DC method.

 As far as straight battery to battery (NO fancy DC DC) using the engines alternator to charge house batteries that TYPICALLY IN  MY EXPERIENCE does NOT provide the quality or quantity of charge as a Smart 3/4 Stage RV converter/charger.  

 Best wishes yall

John T

 

[jcussen]

1 hour ago, Lou Schneider said:

The Renogy DC to DC battery charger produces it's full charging current with inputs as low as 8 volts - that's a 40% voltage drop if the alternator is putting out 13.5 volts.

This makes the voltage drop loss along the charging wire irrelevant.  You'll never see that much loss unless the charging wire is running red hot and melting it's insulation.  

I guess you are suggesting putting the dc-dc charger in the trailer and letting the 10 gauge wire from the trucks alternator feed the charger. From actual experience, the dc-dc charger I mentioned will accept 35 amps and output 30. You may be comfortable with running 35 amps through 30 feet of 10 gauge, but I have seen too many overloaded burnt wires to be comfortable with that. I have cut corners in the past, and not followed the recommended dc wiring ampacity charts, and have regretted it.

[jcussen]

2 hours ago, oldjohnt said:

Glenn, It depends on WHERE the DC to DC charger is located. If its right at the house batteries IE short output charge wire, that reduces output line voltage drop from charger to batteries. HOWEVER, if its located at the energy source (like near the engine alternator) and far from the house batteries, then there will be more output line voltage drop all (either end) subject to Current,,,,,,,,,,,Wire Size,,,,,,,,,,,,Length of wire.

I interpret Lou's post as saying even if there's a lot of line voltage drop from alternator to a DC to DC charger (like say it was located way back at the house batteries far from alternator OR a small wire was used) and even if its down to 8 volts, the house batteries can still get "some" charge via the DC to DC system operation.    

REGARDLESS, one should avoid line voltage drop on EITHER side of the DC DC charger, Input or Output, as that's wasted I Squared R heat energy grrrrrrrrrrrrrrr...........The more the current, the greater the distance, the smaller the wire THE GREATER THE VOLTAGE DROP on either side of the DC to DC.

i agree if the charge wire from say an engine alternator all the way back to a rear RV plug, especially if 10 Gauge wire is used, can subject to length and current, reduce the charging capacity. I'm talking about a straight battery to battery connection  here  NOT an improved DC to DC method.

 As far as straight battery to battery (NO fancy DC DC) using the engines alternator to charge house batteries that TYPICALLY IN  MY EXPERIENCE does NOT provide the quality or quantity of charge as a Smart 3/4 Stage RV converter/charger.  

 Best wishes yall

John T

 

Good info John,  the advantage {or disadvantage] of many lithium batteries is that they will take a 1C charge when their voltage is low. So for two 100 amp lithiums, they will accept 200 amp charge. Lead Acid is completely different and charge rates are a lot lower so you must size your wire for the possible charge rate.

[hemsteadc]

In the long run for otr charging solar is best.

[oldjohnt]

On 8/23/2020 at 12:40 AM, hemsteadc said:

In the long run for otr charging solar is best.

  Yo hemstead, FWIW I agree. I like to let my solar charge my house batteries when driving in daylight. Sure, using the engines alternator (NOT talking DC to DC Chargers here) can supply some degree of charging (subject to wiring and other factors) to the house batteries, yet as noted above it's likely NOT the quality and quantity as a so called properly matched "Smart" 3 or 4 Stage regulated charger might deliver.  IE  An advantage of using Solar is if coupled with a "Smart" 3 or 4 Stage MPPT Charge Controller, its probably better regulated then using the engines alternator (and whatever wiring method) and its charging scheme for the the deep cycle house batteries.

 My method is to let my panels and MPPT controller charge my house batteries when the sun shines, but if I'm driving at night (seldom) then if its even needed (probably not) I flip a switch which basically ties my lead acid house batteries and lead acid engine battery together. While that's NOT as good as a DC to DC Charger (considering a purchase but its not something I really need) in my opinion, its an available option all subject to wiring methods.  I would NOT use such a system if my house batteries were Lithium.

 As an example, my MPPT alone (subject to battery SOC) may charge at 14.4 + volts for some time, then drop to around mid 13 volts,  then settle in and float at something like 13.2 volts. With no sun and coupled to my engine battery (after driving a while)  the house battery voltage (sure varies with SOC) may be say 12.9 to the low 13 volt range. Of course sure IF NEEDED that still pumps some charging amps into my house batteries. Im NOT saying it cant "work" Im ONLY saying its not the absolute best method in my opinion.............. 

PS The voltages I noted immediately above (driving and batteries effectively in parallel) ARE DIRECT ON THE HOUSE BATTERIES Id guess its higher on the engine battery (perhaps 13+ to even 14 depending on the alternators regulation scheme, SOC, and house battery current draw) as there can be some line voltage drop in the 8 Gauge 10 ft run wires from engine to house batteries. NUFF SAID 

 Take care, fun sparky chatting with all of you.

John T  

Edited August 24, 2020 by oldjohnt

[hemsteadc]

12 hours ago, oldjohnt said:

  Yo hemstead, FWIW I agree. I like to let my solar charge my house batteries when driving in daylight.  

My cat rides in the 5er and to keep her cool I run air on hot days.  83° seems to work fine and doesn't overtax the system. 800w of solar doesn't do the whole job, but it does enough.

Edited August 25, 2020 by hemsteadc

[30West]

I’m confused. Are you folks referring to the trickle through the 7 pin connector or a separate wire dedicated for charging? If 7 pin exactly how would you disable it?

[GlennWest]

5 minutes ago, 30West said:

I’m confused. Are you folks referring to the trickle through the 7 pin connector or a separate wire dedicated for charging? If 7 pin exactly how would you disable it?

The camper umbilical cord usually go to a set of fuses. If so, just removed it.