Differing batteries

[Scott'n'Wendy]

While reading another thread, I was given a sniff of info about dc/dc chargers. Which led me to Yoda's DC/DC install project, which leads me to the following question.
What negative effects, if any, occur when my TV has an FLA or AGM battery and my trailer has a LiFePO4 battery while I roll down the road? No other electrical mods other than installing the LiFePO4 in the trailer.

[Jkwilson]

Not going to matter.

[howson]

While reading another thread, I was given a sniff of info about dc/dc chargers. Which led me to Yoda's DC/DC install project, which leads me to the following question.
What negative effects, if any, occur when my TV has an FLA or AGM battery and my trailer has a LiFePO4 battery while I roll down the road? No other electrical mods other than installing the LiFePO4 in the trailer.

Jkwilson (John), of course, is right.

Using my setup as an example, the reason is the Renogy DC-DC Charger effectively isolates the two different batteries. My Ford will charge it's batteries appropriately (as intended by the OEM) and the Renogy takes the incoming 12v and properly conforms the output to charge the Battle Borns.at the right voltage level.

[Scott'n'Wendy]

Thanks Gents
The electrician in me was wondering of the effects of having a low input resistance load in parallel with a higher resistance load coupled to an alternator. Both potentially having high current demands..at the same time.

[Jkwilson]

Thanks Gents
The electrician in me was wondering of the effects of having a low input resistance load in parallel with a higher resistance load coupled to an alternator. Both potentially having high current demands..at the same time.

With the wire size and length of the 12V charge circuit on the trailer plug, the lithium battery will get around 8A max.

[Country Campers]

I thought the question was " with out any dc-dc charger what effect does the TV charge system have on the Lithium battery?", is this the original question?

The charging profile for the TV is much different than that of Lithium as well as the cell difference between Lithium and others, AGM or wet cell batteries.

Brian

[Jkwilson]

I thought the question was " with out any dc-dc charger what effect does the TV charge system have on the Lithium battery?", is this the original question?

The charging profile for the TV is much different than that of Lithium as well as the cell difference between Lithium and others, AGM or wet cell batteries.

Brian

The idea of charging “profiles” is largely mistaken because charger manufacturers describe charger operation as if it requires careful engineering and intelligence in the charger. To charge a battery, you apply a DC voltage that is higher than the current voltage of the battery. Period. The charger never does anything or changes its output in any way until the charging process is complete. In order to prevent battery damage, the voltage is generally limited by the charger to a value that is higher than the fully charged voltage of the battery yet not so high that it damages the battery. It is often the case that the same voltage works fine for both lithium and lead-acid batteries.

Most chargers also monitor the charging current as an indication of battery state of charge. Typically when charge current drops below 1A, the charger terminates the charge. It may also start a float charge for maintenance, but this is not part of the charging process.

Chargers do not have bulk mode, absorption mode, constant current mode or constant voltage mode that charger manufacturers claim as stages. These modes are all just descriptions of normal behavior that any fixed voltage DC power supply would exhibit if connected to a battery.

The charging system in a vehicle operates slightly differently, as it is primarily supplying power to operate the vehicle and adjusts its output based on the load. A battery, whether lithium or lead-acid is simply another load to which the vehicle voltage regulation system responds.

A constant DC power supply with voltage regulation around 14.6V will charge either a lead-acid battery or a lithium battery.

[howson]

Jkwilson

Maybe I misunderstand the component being defined as a "charger" in post #7, but the Victron Multiplus has Bulk, Absorption and Float modes that specifically change the output voltage applied to the battery based on it's type and battery voltage level.

Reinout Vader, the founder of Victron, has written a book called Energy Unlimited (available for free). The book has an entire chapter on Battery Charging: the theory. It goes in-depth on the topic of how and why batteries are charged according to their type and in different situations. Below is a quote from the chapter's introduction:

4.1. Introduction
Writing about battery charging would be easy if there was one recipe, independent of the conditions of use and valid for all types of lead acid batteries. But this is not the case.

Additional complicating factors are that there is often more than one charging device connected to the battery, and that the net charging current is not known because of consumers that are also connected to the battery.

Voltage limited charging is the best way to eliminate the influence of consumers as far as possible. And working with 2 voltage limits, the absorption and float voltage limits discussed later in this chapter, is a good and generally accepted method to charge batteries which have been deeply discharged, as fast as possible.

A further refinement of the standard 3 stage (bulk – absorption – float) method is adaptive charging: see sect 5.3.2.

The book then goes on at length discussing the different "C" levels appropriate for different size battery banks and battery types. (For those who are curious about "C" rates, see https://batteryuniversity.com/articl...what-is-c-rate ).

The specific statement I'm wrestling with from your post is, A constant DC power supply with voltage regulation around 14.6V will charge either a lead-acid battery or a lithium battery. As a stand-alone statement that is true since electrons will flow to a discharged battery from a regulated 14.6vDC power source. But, and it's not a trivial matter IMHO, the battery may not be charged correctly, and in some cases even to the battery's detriment if I understand what Vader is conveying in his book.

Energy Unlimited is available here: https://www.victronenergy.com/upload...limited-EN.pdf

Howard

P.S. Took me awhile to write this response--hope it is received in the spirit intended.

[Scott'n'Wendy]

I thought the question was " with out any dc-dc charger what effect does the TV charge system have on the Lithium battery?", is this the original question?

Yes, along with the TV battery. Two differing construction batteries, connected in parallel without the benefit of DCDC charger isolation. Will it harm either battery?

Jkwilson and Howson's answers suggest to me both batteries be fine with the only negative being lithium getting charged like a FLA battery.

[Guest]

The idea of charging “profiles” is largely mistaken because charger manufacturers describe charger operation as if it requires careful engineering and intelligence in the charger. To charge a battery, you apply a DC voltage that is higher than the current voltage of the battery. Period. The charger never does anything or changes its output in any way until the charging process is complete. In order to prevent battery damage, the voltage is generally limited by the charger to a value that is higher than the fully charged voltage of the battery yet not so high that it damages the battery. It is often the case that the same voltage works fine for both lithium and lead-acid batteries.

Most chargers also monitor the charging current as an indication of battery state of charge. Typically when charge current drops below 1A, the charger terminates the charge. It may also start a float charge for maintenance, but this is not part of the charging process.

Chargers do not have bulk mode, absorption mode, constant current mode or constant voltage mode that charger manufacturers claim as stages. These modes are all just descriptions of normal behavior that any fixed voltage DC power supply would exhibit if connected to a battery.

The charging system in a vehicle operates slightly differently, as it is primarily supplying power to operate the vehicle and adjusts its output based on the load. A battery, whether lithium or lead-acid is simply another load to which the vehicle voltage regulation system responds.

A constant DC power supply with voltage regulation around 14.6V will charge either a lead-acid battery or a lithium battery.

Automotive charging systems do not operate at the constant voltage that is required for lithium charging. Also auto systems will not deliver the higher voltages that are required for a lithium battery to balance since they are designed to top balance the cells toward the end of a dedicated lithium charge profile. So will an auto charge a lithium battery as well as a converter designed for FLA? Yes. But not efficiently where eventually the lithium battery will end up unbalanced with reduced longevity.

Look at the graph on a Victron BMV-712 app while a dedicated lithium charger is doing its job and it can be seen that an auto charge system will not precisely control like a dedicated lithium based charger.

Jim

[howson]

Yes, along with the TV battery. Two differing construction batteries, connected in parallel without the benefit of DCDC charger isolation. Will it harm either battery?

Jkwilson and Howson's answers suggest to me both batteries be fine with the only negative being lithium getting charged like a FLA battery.

Wiring two different battery types directly together in any configuration is not recommended. Even the same battery type (wired in series or parallel) should be avoided if not purchased at the same time. (LifePO4 has some leeway in this, but not much more than a year.)

The confusion may be in thinking that a trailer's battery is wired "in parallel" with the TV's battery through a modern TV's 7-pin connector. That's not the case. Through some gee-wizardry the auto engineers limit the amount of power that can be transmitted through the 7-pin connector, thus the trailer's battery is isolated from the TV's battery. That's why, even when my Battle Borns could have accepted much more, my Ford's 7-pin output was a measly 9 amps.

I could not have this 100% right (rarely do), but here's what I think I know: a LifePO4 will charge from a modern tow vehicle through the 7-pin connector without any harm, but at a very low rate. Thus the term "trickle charge". That is the genesis for why I pursued a DC-DC Charger as documented in my install thread: https://gdrvowners.com/forum/operati...e-battle-borns

Howard

[familytruckster4]

In the past I have rewired the trailer feed source on my trucks so that the 12v feed from the truck is disconnected when the ignition is off. This was to prevent the truck battery from being used when we stopped for rest while on the road. This way I didnt have to disconnect the 7 way plug.
Given the complexity of the new trucks as far as charging systems and the advent of AGM batteries in the trucks, should I be looking to do that with my 2021 to prevent any problems since my trailer batteries are plain old wet cell ?

[Guest]

Wiring two different battery types directly together in any configuration is not recommended. Even the same battery type (wired in series or parallel) should be avoided if not purchased at the same time. (LifePO4 has some leeway in this, but not much more than a year.)

The confusion may be in thinking that a trailer's battery is wired "in parallel" with the TV's battery through a modern TV's 7-pin connector. That's not the case. Through some gee-wizardry the auto engineers limit the amount of power that can be transmitted through the 7-pin connector, thus the trailer's battery is isolated from the TV's battery. That's why, even when my Battle Borns could have accepted much more, my Ford's 7-pin output was a measly 9 amps.

I could not have this 100% right (rarely do), but here's what I think I know: a LifePO4 will charge from a modern tow vehicle through the 7-pin connector without any harm, but at a very low rate. Thus the term "trickle charge". That is the genesis for why I pursued a DC-DC Charger as documented in my install thread: https://gdrvowners.com/forum/operati...e-battle-borns

Howard

Howard,

I have to respectfully disagree. The 7 way connector as wired to the trailer is parallel wired to the TV. Both batteries will share a positive and negative connection in its original wiring configuration. The DCDC will isolate this parallel connection.

For reasons that I can only assume is geared toward sales, BB consistently provides advice that is counter productive to LifeP04 longevity. And they are the only ones that I have found that does this. Discharging fully, charging in parallel to lead acid types via a 7 way, and storing at 100% SOC are a few examples that are incorrect.

Jim

[Country Campers]

This is a great discussion and I hope it keeps going as I am learning.

One of my contacts at GD , which I wrote a question to a while back responded with this information, trimmed down out of an email, quoted.

"Lets start with wet cell batteries like the one in your truck and the one your alternator is designed for.
With a good (12 volt) battery each cell will have 2.13 volts per cell. A (12 Volt) battery has 6 cells. So real numbers a good wet cell battery fully charged should read 12.78 volts at rest with no loads. In order for the charging voltage to push the proper amount of amperage into these batteries the voltage must be one half of a volt above a standing charge or 13.28 volts minimum. That is what some call trickle charge. I call it float charge.
Maximum or Bulk charge will be 14.4 volts.
That’s what your wet cell battery and alternator are designed for. 13.28 to 14.40.
A lithium battery needs one and a half volts above a standing charge minimum so, float charge on lithium would be 14.28 volts. Max charge or bulk charge will be 15.48 volts.
As you can see max for a wet cell is 14.40, minimum for a lithium is 14.28. when you plug in the 7 way to the truck you are putting all batteries in parallel.
The alternator/regulator in your truck will not charge a lithium correctly. It will work itself to death. I have heard of people using a dc to dc converter to correct this but, I do not have enough experience yet to say one way or the other if this would be a good choice for you.
The other problem you will have is if you haven’t up graded your converter you will have the same issues. The standard converter currently installed is designed for wet cell batteries. It will have to run wide open throttle just to maintain or trickle charge lithium batteries and the more batteries you have the longer it has to run at wide open."

I partially understand most of this but maybe it will further this discussion.

Brian

[howson]

Howard,

I have to respectfully disagree. The 7 way connector as wired to the trailer is parallel wired to the TV. Both batteries will share a positive and negative connection in its original wiring configuration. The DCDC will isolate this parallel connection.

For reasons that I can only assume is geared toward sales, BB consistently provides advice that is counter productive to LifeP04 longevity. And they are the only ones that I have found that does this. Discharging fully, charging in parallel to lead acid types via a 7 way, and storing at 100% SOC are a few examples that are incorrect.

Jim

There has to be something in the truck's electronics that limits the charge going through the 7-pin, Jim. Why, when the Battle Borns are discharged below the TV's battery voltage (and the alternator's) was the current output from the 7-pin limited to 9 amps? If the batteries were in parallel, there'd be a huge rush of current from the truck to the trailer as the batteries tried to balance out.

It's OK if we disagree (and I find it hard to argue with an auto engineer, lol) but the truck and tow vehicle's batteries cannot be directly wired in parallel. Can't be. If they were there'd be blown fuses or melted wires as the Battle Borns would accept up to 1C (100 amps) before it's built-in BMS shut it down.