DC/DC Isolation Charger

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DC/DC Isolation Charger

August 16, 2021, 10:09:23 pm

I am in the process of converting over from AGM to LiFePO4 batteries. I do not plan to add solar at this time, that may come later. My first step is to replace the old diode based battery isolator with DC/DC isolated charger. The wiring diagram that seems to apply to my installation is the one in the image below. The first question is if this looks correct and if so, does the sense wire from the Leece-Neville alternator connect into the start battery positive wire after the fuse.

Any thoughts or opinions appreciated.

Richard

Re: DC/DC Isolation Charger

Reply #1 – August 16, 2021, 11:59:19 pm

Quote from: Jan & Richard – August 16, 2021, 10:09:23 pm

...does the sense wire from the Leece-Neville alternator connect into the start battery positive wire after the fuse.

My thought on the second half of your question (the only part I feel even slightly qualified to answer):

It should not matter if the sense wire is connected before or after the fuse on the start battery positive post. As long as the fuse remains intact, the alternator will see start battery voltage.

Re: DC/DC Isolation Charger

Reply #2 – August 17, 2021, 01:29:45 am

Richard, the Orion DC to DC charger is a nice choice. The fuses are there to protect wiring and equipment from shorts or mishaps. Generally you want a fuse close to the source of power. When connecting to batteries with charge sources lots of devices suggest a fuse at both ends. But close to the battery is always a good choice. The Orions have nice built in protection as well.

These chargers can be set to sense "engine on" by monitoring alternator voltage. They can also have an on off switch which is useful with solar. Without solar you will probably want to be charging while driving anyway. You can wire in a delay timer to the on/off switch that sense ignition and closes the switch circuit after say five minutes to help quickly recharge the start batteries and the start charging both.

The sense wire as originally wired comes from the start batteries through a circuit breaker and then to the LN Sense Post. No need to change that.

You can remove the old isolator and put the Orion in its place. Add a one or two post bus bar and connect the alternator to the post and from there to the start side of the boost switch. From that post you also wire to the + side of the input of the Orion. The output C side of the Orion can go to the house side of the boost switch just as the two outputs of the OEM isolator does now.

Ground sides of both batteries are common so I don't think it makes any difference how or where you connect the ground side of the input and the ground side of the output. The non-isolated version uses a common ground.

When the Orion is off the two battery sets are isolated.

Re: DC/DC Isolation Charger

Reply #3 – August 17, 2021, 09:08:46 am

Thank you Roger,

I Knew you could and would provide this detailed clarification on the wiring. Initially I thought I would email you directly with my question but then decided to post the question here so that your reply may help others besides me.

Richard

Re: DC/DC Isolation Charger

Reply #4 – August 17, 2021, 02:22:41 pm

Without solar (that can be added anytime) the Orion charges your LiFePO4 batteries using a multistep smart charge profile. Its only limitation is the 30 amp maximum charge rate. BattleBorn suggest limiting charge rate to 20% of maximum capacity which can extend their lifetime charge cycle count by almost 50%. If you have 400 amp hrs capacity then the max charge rate would be 80 amps. You can add a second Orion (or more) to increase the total charge rate. I don't know if they coordinate charging.

We have a Sterling Battery to Battery charge, same idea, 60 amps. For our 600 amp LiFePO4 capacity that is 10% of total capacity. After a 16 hr overnight stay at a WalMart in January a couple years ago and a 6 hr drive in pouring rain e
We were just approaching 100 SOC. If the sun had been out it would have only taken 3-4 hrs. Of course we could have started the generator but didn't. Most of the time I don't even turn it on while driving, solar is sufficient.

Re: DC/DC Isolation Charger

Reply #5 – August 17, 2021, 03:05:52 pm

Don't think I will have a problem keeping below 20% of capacity for charge rate. The two batteries I have built up are 280 each for a total of 560 amp hours capacity. To exceed 20% I would have to exceed 112 amps at 12 volts.

Richard

Re: DC/DC Isolation Charger

Reply #6 – August 17, 2021, 03:58:05 pm

Richard,
What kind of batteries did you end up deciding to use?

Re: DC/DC Isolation Charger

Reply #7 – August 17, 2021, 05:10:15 pm

Also interested in battery build. This is on my short list.

Re: DC/DC Isolation Charger

Reply #8 – August 17, 2021, 06:52:43 pm

I chose to go with 280 amp hour cells which are available from numerous vendors online. I ordered mine from Solar Supply House in San Diego.

Re: DC/DC Isolation Charger

Reply #9 – August 17, 2021, 10:14:35 pm

Looking good! Did you have to top balance them or were they done already? Which bms are you using? Like the straps!

Re: DC/DC Isolation Charger

Reply #10 – August 17, 2021, 10:34:36 pm

Those should work. Set of Four Matched LiFePO4, 280AH, 3.2V Lithium Prismatic Cells for DIY...
Price is good, size is good.

What are you using for a BMS? Their battery box looks like a nice way to keep things tidy and protected. Kind of pricey for a plastic box.

I would suggest wiring each battery to a bus bar with cables that are about the same length. Switches help isolate batteries when needs. Fuse on the plus side, shunt on the negative side.

You can get rid of the upper rack in the battery bay, save 50 lbs. I made a new rack for the lower portion using lighter steel, probably another 30 lbs. Be sure to provide a secure hold down for the batteries. Gravity is insufficient with these lightweight batteries.

Re: DC/DC Isolation Charger

Reply #11 – August 17, 2021, 11:52:24 pm

I had not thought about needing tie downs because of the batteries' lighter weight. Also, I reconfigured the upper battery level to accommodate the different shape and size of the new batteries. I figured I could then use the lower portion of the bay for storage.

As to the BMS's, they seem to be in short supply at the moment. I have two of the type TommyD has, but they are on back order. They will probably not get here before we leave the coach until the end of the year. So this project will be in limbo for a while.

Richard

Re: DC/DC Isolation Charger

Reply #12 – August 20, 2021, 12:28:20 pm

I've been working on charging my lithium Bank off the alternators now for a while. Been in contact with American power systems in Iowa thinking about putting in a larger alternator so I can run my rooftop air off the alternator while charging the battery Bank going down the road. When I am solar put my lithium system in a disabled being able to charge it off the alternator to prevent damage to the alternator. I thought about a simple DC to DC charger from victron but wasn't quite sure that is what I wanted to go with. I also looked into their buck boost 100 amp charger DC to DC converter but at over a $1,000 it was pretty pricey but it is programmable. I have an awful lot of money invested in my victron lithium system that I want to make sure it's done right. American power systems not only makes the alternators but they make the external controllers that work with lithium battery systems. Will be more pricey than just going with a straight DC to DC charger but we'll see... Hopefully it'll come up with a decent system for me that won't break my bank. Meanwhile the search for the dash air continues.

Re: DC/DC Isolation Charger

Reply #13 – August 20, 2021, 10:29:51 pm

Today I removed my old diode isolator and installed the DC/DC isolator. Upon close inspection the diode isolator showed signs of significant overheating at the post for the chassis battery. I suspect it was on the way to failing. This may be something that should be looked at if you still have the 20+ year old diode isolator. Obviously I had never looked closely at it before.

Richard

Re: DC/DC Isolation Charger

Reply #14 – August 22, 2021, 08:33:17 pm

Next question: While preparing to mount my new DC/DC charger, I noticed my faithful Trik-L-Start which I had not thought about in years.

My coach often spends weeks or even months plugged into shore power but not moving. At those times the inverter/charger historically kept the house batteries float charged directly but not the start (chassis) batteries. The Trik-L-Start moves power around the battery isolator to the start batteries to keep them topped up.

I understand that Lithium batteries do not like to be float charged so my charger will not provide that stage of charging. If I reconnect the Trik-L-Start around the DC/DC charger as it was around the battery isolator, the AGM start batteries will be maintained by my house Lithium batteries drawing them down over time. The inverter/charger will not kick back in until a threshold of 12.5 volts on the house batteries is reached. It should then recharge the Lithium batteries and start the cycle over again.

If this is a problem, the only other option I can see is not to have the Trik-L-Start and to install a separate small trickle charger on the engine start batteries.

Any thoughts or recommendations?

Thanks,

Richard

Re: DC/DC Isolation Charger

Reply #15 – August 22, 2021, 09:01:21 pm

Different from my lithium batteries. recommended float charge 13.8 volts.

Re: DC/DC Isolation Charger

Reply #16 – August 23, 2021, 09:56:00 am

I have a Sterling ProCharge Ultra 40 amp smart charger. Sterling ProCharge Ultra 40 Amp Boat Battery Charger

I added it when I had 2 house battery banks (>1500 ah) and the start batteries. It charged all three. Now two outputs are combined to my LiFePO4 batteries and are set for Lithium batteries and the other is connected to the start batteries. If we are plugged in somewhere the big inverter/charger is off and this charger adds what ever is needed in addition to solar charging. It rarely operates at full capacity and puts itself into a deep sleep mode when charging is not needed but wakes up enough to check every once in a while to see if it needs to come back on.

You should be able to set charging parameters on your charger/inverter to a Lithium friendly profile. A trickle charger should work OK. The same B2B charger you have for charging your lithiums from the alternator can be used the other way to charge the start batteries using the Lithiums as the source. Start battery loads are there while at rest but are small, 15 amps would be plenty.

A Victron Multiplus has a start battery charge connection built-in. It is a 4 amp maintenance charger. Probably enough for our coaches.

Another one of those tasks with lots of options for a good outcome but the start batteries need something.

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DC/DC Isolation Charger

August 16, 2021, 10:09:23 pm

Re: DC/DC Isolation Charger

Reply #1 – August 16, 2021, 11:59:19 pm

Re: DC/DC Isolation Charger

Reply #2 – August 17, 2021, 01:29:45 am

Re: DC/DC Isolation Charger

Reply #3 – August 17, 2021, 09:08:46 am

Re: DC/DC Isolation Charger

Reply #4 – August 17, 2021, 02:22:41 pm

Re: DC/DC Isolation Charger

Reply #5 – August 17, 2021, 03:05:52 pm

Re: DC/DC Isolation Charger

Reply #6 – August 17, 2021, 03:58:05 pm

Re: DC/DC Isolation Charger

Reply #7 – August 17, 2021, 05:10:15 pm

Re: DC/DC Isolation Charger

Reply #8 – August 17, 2021, 06:52:43 pm

Re: DC/DC Isolation Charger

Reply #9 – August 17, 2021, 10:14:35 pm

Re: DC/DC Isolation Charger

Reply #10 – August 17, 2021, 10:34:36 pm

Re: DC/DC Isolation Charger

Reply #11 – August 17, 2021, 11:52:24 pm

Re: DC/DC Isolation Charger

Reply #12 – August 20, 2021, 12:28:20 pm

Re: DC/DC Isolation Charger

Reply #13 – August 20, 2021, 10:29:51 pm

Re: DC/DC Isolation Charger

Reply #14 – August 22, 2021, 08:33:17 pm

Re: DC/DC Isolation Charger

Reply #15 – August 22, 2021, 09:01:21 pm

Re: DC/DC Isolation Charger

Reply #16 – August 23, 2021, 09:56:00 am

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