Seeking feedback on my lithium upgrade plan

[jbeard4]

Hi everyone,

The original AC-DC transformer in my 1966 Airstream Caravel failed, and I would like to replace it with a new 12V Charger-Converter, and upgrade the old lead acid battery to a new 100Ah Battleborn LifePO4 battery. I am pretty new to electrical work, so I wanted to describe my plan to see if anyone has any feedback, before I start ordering components.

Here's a description of the original electrical system:

• The AC circuit that feeds the DC converter is 120V at 20A.
• The original transformer outputs 12V at 25A, and 19V at 20A. I believe the 19V system is no longer used (it still connects to the low voltage distribution panel, but there are no longer any appliances left in the trailer that use the 19V input).
• Finally, it's using 12 AWG wiring everywhere.

My plan is to swap out the original transformer for a PowerMax PM3-15LK, which is a 12V 15A charger-converter. The reason why I chose this particular model was because of the low amperage. Most of the popular converter brands (e.g. Progressive Dynamics, Go Power!, etc.) seem to make charger-converters that output a minimum of 30A. This is 5A more than the original transformer, and it wasn't clear whether it would be safe to use with the original 12 AWG wiring. I could run new wiring at a lower gauge, but that would require rewiring the low-voltage panel, which is something I don't want to do. So I chose the 15A charger-converter because it is 10A below the amperage of the original transformer, and therefore should be safe to use with the all of the original wiring.

I also chose this unit because BattleBorn has an article describing how to calibrate it for their batteries, so I feel like it should be a pretty safe bet in terms of compatibility.

In terms of installation, I believe it would involve the following steps:

1. Use the original AC input wiring to wire a new AC electircal outlet for the converter to plug into;
2. Then wire the original 12V DC wiring into the converter's screw terminals
3. Then tune the ouput voltage in the converter, per battleborn's instructions
4. Finally swap out the old lead acid battery for the new BattleBorn battery and wire up the existing lugs to the new battery terminals

And that's it! I would appreciate any advice anyone can share on this. Thanks for your time and attention,

Jake

[richard5933]

I think that you're planning too small of a converter/charger.

If my understanding of what you say is correct, you have a 120v circuit protected by a 20-amp breaker. That circuit feeds the converter/charger with 12 ga wiring.

You can safely run a much larger converter/charger on that circuit, even one with an output of 60 amps @ 12vdc or higher. Look at the spec sheet for your new converter/charger and you'll see that the 60-amp model only pulls 875 watts, which is well below the limits for your 20-amp AC circuit.

Sounds like you're confusing the output rating in amps of the converter/charger with the input limits of it on the 120v wiring. Important to remember that to make, for example, 50 amps @ 12vdc on the output side the converter/charger will only need about 5 amps at 120vac. This is the converter part of the unit - it converts the high voltage/low amperage from shore power into low voltage/high amperage to the DC side.

One of the nice things about lithium batteries is their ability to take a charge quickly, so it would be a shame to cripple them with a tiny charger. No need to go excessive on the charger, as that will possibly draw so much that it leaves little current available to run other 120v devices while bulk charging, but you should be able to safely run something larger than what you're planning.

[jbeard4]

Originally Posted by richard5933

I think that you're planning too small of a converter/charger.

If my understanding of what you say is correct, you have a 120v circuit protected by a 20-amp breaker. That circuit feeds the converter/charger with 12 ga wiring.

You can safely run a much larger converter/charger on that circuit, even one with an output of 60 amps @ 12vdc or higher. Look at the spec sheet for your new converter/charger and you'll see that the 60-amp model only pulls 875 watts, which is well below the limits for your 20-amp AC circuit.

Sounds like you're confusing the output rating in amps of the converter/charger with the input limits of it on the 120v wiring. Important to remember that to make, for example, 50 amps @ 12vdc on the output side the converter/charger will only need about 5 amps at 120vac. This is the converter part of the unit - it converts the high voltage/low amperage from shore power into low voltage/high amperage to the DC side.

One of the nice things about lithium batteries is their ability to take a charge quickly, so it would be a shame to cripple them with a tiny charger. No need to go excessive on the charger, as that will possibly draw so much that it leaves little current available to run other 120v devices while bulk charging, but you should be able to safely run something larger than what you're planning.

Hi Richard,


Thank so much for your reply. I think the reason why I thought that the 12 AWG wiring would support less than or equal to 25 amps is because of this chart I found on the BattleBorn FAQ under "How do I know what size cable to use in my system":






My reading of this chart is that 0-4 feet of 12 AWG wiring would support 20-25 Amps. I assume this is for 12V.


This matched up with the output amperage of the original transformer, so it seemed to make sense. Am I misreading this? Or is the chart wrong?


Thanks again for your help with this,


Jake

[richard5933]

Is the 12 ga wiring you're talking about feeding the 120v power to the converter/charger or is it taking the output of the converter/charger and feeding it to the batteries?

If it's the wiring feeding the 120v to the converter/charger, then you're fine with installing a larger one like I mentioned earlier. If you're talking about the wiring between the converter/charger and the batteries (or the DC distribution panel) then you'd need something larger than 12 ga to run any converter/charger worth installing.

Most converter/chargers are installed near the batteries. This makes it easy to run properly sized wiring between the converter/charger and the batteries. I have 6 ga wiring between my converter/charger and the 12vdc distribution point. If you only have 12 ga wiring handling the DC output of the converter/charger, then that needs to be updated if you want to charge the lithium batteries in a realistic time frame.

There's no point going through all this only to install a converter/charger with less output than you need. A 15-amp converter/charger might have all its available output consumed just running the lights and other devices inside the trailer and not have anything left to charge the batteries with, so I'd consider that a non-starter.

[1StreamDream]

My line of thought on your scenario is very much in line with Richard, I think you will be much better served (and happier in the long run) with a higher amperage converter/charger. Part of my trade-off based analysis is based on how I use my system, your use might be very different, but consider this. In any scenario where you might use generator power (ie Honda or equivalent) to re-charge your batteries, such as boondocking, the higher amperage will mean you restore the battery to at or near 100% charge much faster. Same is true if you temporarily connect to 120VAC shore power ... recharge much faster. I have needed that (generator scenario) because many of the places I have been had restricted hrs for generators, like 8am-10am and 5pm-8pm, so you have a limited time to accomplish battery replenishment. Also agree that you want larger gauge wire, you mention you dont want to re-wire your DC panel but I think you are only talking about 2 wires here, not the whole panel. I would do a minimum of 10ga wire between the DC panel, and the batteries, and if you are going to buy new cable, I strongly suggest you get silicone insulated, it is far more flexible that stranded THHN you get at the big box stores. The wire flexibility is invaluable when routing in tight spaces like the airstream. Also 10ga can be done with most handyman tools, if you go bigger, you might need to buy a special tool to crimp lugs on the end. Temperature rating is *not* the concern, the flexibility is the key. Something like this is what I suggest .... https://www.amazon.com/BNTECHGO-Sili...01FQIYWRM?th=1

[jbeard4]

Originally Posted by richard5933

Is the 12 ga wiring you're talking about feeding the 120v power to the converter/charger or is it taking the output of the converter/charger and feeding it to the batteries?

It's using 12 ga wire for both the 120V input and the 12V output.

Originally Posted by richard5933

Most converter/chargers are installed near the batteries. This makes it easy to run properly sized wiring between the converter/charger and the batteries. I have 6 ga wiring between my converter/charger and the 12vdc distribution point. If you only have 12 ga wiring handling the DC output of the converter/charger, then that needs to be updated if you want to charge the lithium batteries in a realistic time frame.

It is close to the battery.

Originally Posted by richard5933

There's no point going through all this only to install a converter/charger with less output than you need. A 15-amp converter/charger might have all its available output consumed just running the lights and other devices inside the trailer and not have anything left to charge the batteries with, so I'd consider that a non-starter.

Thanks, this is a useful insight, and I agree with your assessment.


I have an idea that I wanted to run by you:

I feel pretty confident running new 6 ga wiring from the converter directly to the battery.
However, I really want to avoid running a higher amperage into the existing low-voltage panel. I don't understand the wiring in the low-voltage panel very well, and I think it would be outside of my current skill level to rewire it safely. I would hire someone to rewire the low-voltage panel for me, but it's hard to find someone in my area to do this work.

So, I was wondering if it might make sense to install two new converters: a low-amperage (15A) converter, and a high-amperage (50A) converter. Run the low-amperage converter over the existing 12 ga wiring to the low-voltage panel to power the DC lights when on shore power; and wire the high-amperage converter directly to the battery so that it can rapidly charge the battery. Is that a crazy thing to do? Or is there another way to step down the amperage from the converter when running wiring into the low voltage panel?


Thanks again for all of your advice on this.

[richard5933]

Can you post a photo of your current 12v panel? I suspect that you would have no problem connecting a 50-amp converter directly to it. Your batteries already provide more available power than a 50-amp converter and they should be connected directly to the 12v panel.

This might be a good idea to upgrade your battery cables as well, as many seem to be undersized. What is the gauge of the battery cables right now?

[SilverWind]

This is a very interesting thread. We have a 1968 Caravel. I plan to replace the 45 amp Progressive Dynamics Inteli-Power PD9145A Charge Controller with a 45 amp Inteli-Power PD9145ALV 12V lithium Intelligent Controller. We are planning on either one or two 100Ah Battleborn LifePO4 batteries. Our charging source is either shore power or a Zamp 140 portable solar suitcase.

[let's play]

Simplified, your battery runs your 12 volt system, the converter is essentially chargimg your battery at the rate of converter output. 15 or 55 amp your choice, as others have said, go with a higher output

. The converter will also supply a steady stream of juice up to the amperage rating without drawing any load off the battery. So a higher amperage charger is a benefit to a point.

You should change out the cables from the charger to the battery, hit up a marine store and they can make them for you. Also change out the cables from battery to the 12 volt panel. You ABSOLUTELY MUST install a fuse between the battery and 12 volt distribution panel on the positive cable. Check out West Marine website. Rv systems are very similar

Sounds like a fun project.

[uncle_bob]

Hi

Backing up a bit .... There is nothing special at all about the converter charger you have picked. Indeed it's actually sub optimum since they state it gets used in fixed voltage mode for lithium. That's not the best approach.

As others have mentioned, a bigger converter is generally a better converter. 30 to 50A devices have been "normal" for a very long time. I doubt your original unit was anything less than a 40A unit.

Fuses are what protect wires. Loads are what determine current draw. You can put a 150A converter charger into your existing panel. As long as you put the correct fuse on the output wire to the panel, all will be ok.

Bob

[jimdelane]

The Battleborn wire gauge is for DC amps coming from the battery to inverter or other loads. 25A DC = 2.5A AC. I realize this is not exact but close enough for estimating purposes. Odds are you have nothing that will draw 25A DC.
Also, you should include a shunt based battery monitor in your plans. Something like the Victron SmartShunt or the Victron 712. You cannot depend on lead acid/AGM battery monitors as they use voltage to determine state of charge. Lithiums maintain a constant, higher state of charge right through 90% of discharge. LA/AGM will show a 50% discharge at around 12.2v whereas a lithium will still show 12.8+ volts at 50% discharge. So a LA/AGM monitor will show a high state of charge right up to the point that a lithium will die at.

[uncle_bob]

Hi

What *does* need a heavy chunk of wire?

1) The run from the converter to the battery. This needs to be large to be safe *and* to reduce the voltage drop when the charger is running. It is not uncommon for 6AWG or even 4AWG to show up here.

2) The run from the battery to the distribution panel (or fuse block). Again, the issue is as much about voltage drop as safety. 10AWG is about the smallest you would use here, with 6AWG being more common.

3) The cables between the batteries. Yes, the topic is about a single battery. As you do this or that .... more seem to show up . Two or even four or six are not uncommon.

These are all *12V* wires. We're not talking about 120V wiring, only about the 12V side. With 12V, length gets into the act. A short wire might be a "it's safe" wire gauge. A ten foot run ( so 10 feet of ground and 10 feet of power) might be much larger. The drop in 20' of wire can matter at 12V.

What do various things pull?

Incandescent lighting ( if you have not converted to LED .... you should go to LED ) can pull a lot of amps. Twenty or thirty amps on a circuit is not uncommon ( three or four bulbs ...). LED's get that back down to two or three amps.

Computer / USB charge gizmos. Some of the beasts put out 120 to 150W. That likely means 15 to 20A off of 12V.

An inverter. "Entry level" inverters are in the 200W range. Most stock units in RV's are at least 1,000W. That gets you into the 100A or more sort of range.

Vent fans. They each likely pull about 4A running on high. The pair ( if you have a pair) get you up to around 8A.

There are lots more things one could list ....

Fun !!!

Bob

[jbeard4]

Originally Posted by richard5933

Can you post a photo of your current 12v panel? I suspect that you would have no problem connecting a 50-amp converter directly to it. Your batteries already provide more available power than a 50-amp converter and they should be connected directly to the 12v panel.

Hi Richard, this is a bit more information more than you asked for, but I wanted to post an overview of the current electrical system.

Here's the original AC-DC transformer:




You can see on the transformer that it indicates the power output for the 12V circuit is 25 amps, and the 19V circuit is 20 amps:

Incidentally, I discovered that this transformer was providing 12V and 19V AC power, rather than DC. More on this below.



I have already removed the AC-DC transformer, and here is the original 12 ga wiring, which runs through the wall:




Here is where the wiring comes out of the wall and into the low-voltage panel:



Here are pictures of the front and side of the panel:




I think that what's happening in the panel is: the batteries and alternator are wired into the front of the panel, which has the 40 amp glass fuse. I think that the black cable is from the alternator, and the blue and white cables are from the battery.

The blue wire (the battery charge cable) is spliced to an orange wire, which is then fed into the wiring of the low voltage panel (wired into the busbar):




Here is the original lead-acid battery, which I hope to replace with a lithium battery:



The blue and white wires connect to the battery terminals which go into the wall, and then I think come out of the wall again near the low-voltage panels. The red wire goes directly to the water pump.

Originally Posted by richard5933

This might be a good idea to upgrade your battery cables as well, as many seem to be undersized. What is the gauge of the battery cables right now?

It is unclear what gauge wire is being used between the battery and the low-voltage panel, because it is not labeled. It does look a bit thicker than the 12 ga wiring from the transformer to the panel.




In terms of next steps, I was also looking through old forum posts, and discovered one that was super interesting about this exact topic: https://www.airforums.com/forums/f13...tml#post570184

The poster provides the following advice about replacing the transformer:

Originally Posted by Darol Ingalls

If you wish to replace the old transformer, I would recommend the 30amp Intellipower converter and a gell cell battery. Eliminate the "city power" option on the switch box, leave the switches on "battery power". The converter will supply very adequate power to the 12V system and charge the battery while connected to 120V source. Sorry for the long lecture, but I've done several '66, '67 Caravels this way with great success. Darol

But it's not clear from the post whether he is running power from the converter output directly into the batteries; or if he is running the converter output into the low voltage panel. Also, it's unclear if he's using the existing wiring, or has replaced the wiring. Finally, this post is from 2008, and he's referencing AGM rather than lithium batteries, so this might change things as well (like, the 30 amp charger converter may be appropriate for charging an AGM battery, because it charges slower, but not as good for a lithium battery, because it is able to accept a higher amperage in order to charge faster).

Based on my understanding of the existing wiring, I suspect that he is running the 12V 30A DC power output into the low voltage panel, rather than directly into the battery. I suspect that the way to do this is to connect to the terminals where the alternator is wired, and which is already fused with a 40 amp glass fuse, here:



Then just switch the low voltage panel to battery only.

I don't think that "shore power" mode, where the converter powers the lights directly, would work in this setup. In order for this to work, I think I would need to run the converter output into the low voltage panel to replace the old 12V wiring into the busbar, which you can see here:





Another interesting thing I discovered from this forum post was that the original transformer output 12V and 19V AC power, rather than DC. This means it was not originally designed to charge the batteries from shore power, because there was no DC power present. It was only designed to charge the batteries from the alternator on the car. The lights and fans were then designed to run on either AC or DC power. I found this very interesting and surprising.








So, given this new information, there are two alternate setups that I am considering. Both plans involve using two converters: one converter to output < 25 amps and run into the low voltage panel over the existing 12 ga wiring; and another converter which outputs a higher amperage, either 30 amps or 50 amps depending on the setup, and is used to charge the battery.

The first approach is to wire the 30amp converter output into the low voltage panel. Basically connect it to the terminals where the alternator is wired, and which is fused with a 40 amp glass fuse:



I think this approach would be safe, because the 40 amp fuse implies that it can accept < 40 amp charge. And then the low voltage panel would still work the way it was originally intended - I could use the low voltage panel to switch between battery and shore power.

Alternatively, I could install a 50 amp converter and wire that directly into the battery, with new wiring and a new fuse between the 50 amp converter and the battery. The disadvantage of this approach is that it's not clear to me whether it's safe. Would the 50 amp charge pass through the battery and into the low-voltage panel? And would this then blow the 40 amp fuse?


I would appreciate any insight anyone could share on this.



Thanks so much,


Jake

[richard5933]

First, you only need one converter. If you're installing lithium I'd strongly suggest the 45-amp model and not the 30-amp.

It really doesn't matter if you physically connect the converter directly to the batteries or to the 12v panel for much of this conversation, as either way the batteries AND the 12v panel will be connected electrically to the converter.

Important to remember that the fuses in a system are designed to protect the wiring, not the devices. So in your situation you could install a pair of new bus bars (negative and positive) and use them as the central connection point for your new converter, the batteries, and the 12v fuse panel, and then install appropriate fuses to protect each circuit. Amps get 'pulled' by devices, not pushed by the batteries or converter, so you need fuses sized to protect the wiring as the amps are pulled through the wires.

You need a fuse or breaker at the starting point of a circuit which will protect the wiring downstream from it. Your batteries will connect to the new bus bars with appropriately sized battery cables and on the positive side there should be a larger fuse to protect against a direct short somewhere downstream. This is often referred to as a catastrophic fuse and should be sized for the max total draw you're planning to pull from the batteries and/or the largest charge current you're planning to send to the batteries.

Then your converter would connect to the bus bars with appropriately sized cables, which for a 45-amp converter would be 6 ga wire. The converter has it's own fuse, I believe.

The third leg of your system will be the 12v panel, which should have a master breaker/fuse on the supply line to it as well as individual fuses for each circuit. I'd suggest thinking about getting rid of the two glass fuses and installing a modern fuse block, like something from BlueSea. Feed the new fuse block with an appropriately sized wire protected by its own master fuse, and then all your 12v circuits can connect to it through individual blade fuses. You could also use slow-blow fuses or 12v breakers for your 12v panel if you want to get fancy.