Another Lithium Battery Upgrade - Check My Work?

[86Scotty]

I'm a little late to the party but I have 3 rigs currently running lithium. The first I did was a small system in my wife's Jeep with only a 30A Renogy DC2DC and an 80ah lithium bank for a chest fridge. 3 years later the system is working but I've been unhappy with the Renogy charger from day 1. The phone app sucks and the system is buggy.

Second system I did was my work truck with a giant lithium bank running a mini split AC. I have a Kisae DC2DC with Victron shunt which I've been very happy with. The Kisae works well for me and the Victron shunt/phone app, etc. is amazing.

Third system is also Kisae/Victron. I've used cheap Amazon lithium on all systems.

My point is that I would swap the Renogy and Acopower stuff for Victron/Redarc or one of the top tier brands in my van if I were you. You may not think you care about a phone app/monitoring/history, etc. but it is VERY nice to have and also the quality and customer support of Victron is second to none.

I should also note that I haven't upgraded the OEM alternator in any of these rigs and only have solar on the Jeep at only 80w. The van and my work truck have only 165a factory alternators working fine charging at 40a (adjustable on the Kisae, not the Renogy).

 

[geoffff]

Thanks for sharing your experience!!

• Renogy 60A DC-DC --> I have a Victron 30A replacement ordered. Though this Renogy doesn't have any Bluetooth stuff to fail, I've hear enough criticism of Renogy to void them
• Acopower all-in-one solar charger / inverter --> I'll keep this for now and see how it goes

> only 165a factory alternators working fine charging at 40a (adjustable on the Kisae)

My alternator is only 130A (putting out about 75-80A at idle)

When you say "adjustable", do you adjust your Kisae to a lower current? Does it do so automatically somehow?

 

[86Scotty]

Thanks for sharing your experience!!

• Renogy 60A DC-DC --> I have a Victron 30A replacement ordered. Though this Renogy doesn't have any Bluetooth stuff to fail, I've hear enough criticism of Renogy to void them
• Acopower all-in-one solar charger / inverter --> I'll keep this for now and see how it goes

> only 165a factory alternators working fine charging at 40a (adjustable on the Kisae)

My alternator is only 130A (putting out about 75-80A at idle)

When you say "adjustable", do you adjust your Kisae to a lower current? Does it do so automatically somehow?

You can set the current you'd like to charge your system at in 5A(?) increments. This doesn't mean it does this exactly though since the alternator will ultimately prioritize current depending on the vehicle's needs, or at least that is my understanding.

 

[Scalf77]

So I generally look for a couple of feature in a DC to DC unit. The first and foremost I like to have on/off control. Generally the DC to DC would be off when the engine wasn't running, it is nice to have an easy way to manually turn off if needed.

The second thing I look for is voltage input run requirements. This just means that the DC to DC should act somewhat like the SurePower 1315-200 , Blue Sea 762X. If the alternator input is above voltage X the DC to DC will turn the charger on. If the the voltage drops below voltage x the DC to DC charger will turn off the charging. So if the load on the overall electrical is to high for the alternator to maintain the correct voltage the charger will disable to protect the system.

So if you went down to idle and could know longer support DC to DC charging, it would be disabled until the voltage went high enough to turn itself back on. This works much like the ACR's do Connect above 13.x volts and disconnect below 12.8 volts.

I have a generally love/hate relationship with the KISEA that @86Scotty speaks of. They have quite a few advanced capabilities, but then lack in their "Display Screen' and programing the damn thing always takes me about five tries before I get in sync with it.

The KISEA output can be programmed in 5 amp increments.
The start up voltage is 13.2 volts, and the KISEA will shut off for 5 secs every 3 mins to monitor the voltage. Of course if it drops below 12.8 it will turn off and go back to solar prioritization. If the voltage drops below 11.5 volts during the 3 mins, the KISEA will put itself in a derating mode, lowering the output settings. Actually this is one of the few DC to DC with derating features.

There is an on/off switch that is on the unit, not on the remote. This make it kind of useless. It can be extended, but there is also a way to force the unit into shutdown using the temp port.

The KISEA is either solar or DC charging, it can't do both.

It is a pretty good low cost no frill unit.

The Victron Orion XS 50 amp can be programmed in 1 amp increments. It also has a remote terminal that can be used to turn on and off. The remote will work with the engine shutdown sequence. The orion has similar start up and lock out voltages, they can generally be programmed to the exact values you want in 0.1 volts. In any case it to will to protect your charging system, by shutting off the alternator can't keep up. The Orion also has a turn on delay feature, this will give you a little more time before the charger will come on. The Orion XS 50 also has a VE.Direct port, if you are looking to connect to a GX device.

Being that the Victron XS 50 is a dedicated DC to DC charger, it can be used with a subsequent Solar Charger at the same time, as long as the two unit together don't go above the charging limits of the battery.

 

[geoffff]

I sadly discovered the ACOPower all-in-one unit doesn't actually fit under my rear bench seat. Almost, but not quite. So, I used this as an excuse to switch to Victron for all my stuff.

Here is an update with my current schematic.

 

[Scalf77]

House battery 400A fuse, is to high for 2/0 awg wire. Start Battery 400 amp fuse is to high for #2 awg wire.
Fusing for the output of the DC-DC and and Solar should be at the source (individually) your 40 amp fuse post (DC-DC & Solar Busbar would be to low if solar and DC-DC was being used at the same time. I would also look at using lower gauge wire on the output of bot of those units.

You don't show a fuse of breaker from bus bar to fuse block, you are changing wire size from 2/0 awg to 8 awg. This is a good place for a switchable breaker.

Trickle charge from the Victron Multiplus is always on, I would expect some feedback from DC-DC to cause issues.

Solar needs a dual disconnect switch (switches ground & power at the same time). Especially if having a 80 volt input. It is also a code issue.

You are using a m-series battery disconnect switch for house battery Rated at 300 amps. You are using a E-series 3-position switch on starter battery which is rated for 350 amps.

 

[geoffff]

Wow, thanks for all that! I'll read up on each of your points.

Just when I think I've finally got a handle on everything, turns out there's more to think about!

 

[geoffff]

Thanks again for the detailed advice! I'm learning as I go here, and it's sometimes hard to realize how much I don't know yet.

House battery 400A fuse, is too high for 2/0 awg wire.

I'll switch to 200A fuse to match house battery max output amps: 200A

Start Battery 400 amp fuse is to high for #2 awg wire.

House battery is limited to 200A output. Starter battery can produce far more. I'll put a 200A fuse at starter battery end of this cable. I know this is a bit edgy for 2 AWG cable, but it allows for emergency start.

My Sportsmobile originally came with no fuse for this 2 AWG cable. I have already experienced an engine fire because of it!

Fusing for the output of the DC-DC and and Solar should be at the source (individually)

These chargers can only produce 30A + 35A. So, isn't the bus bar itself the real "source" as it can produce far more current than the chargers, at 200A?

your 40 amp fuse post (DC-DC & Solar Busbar would be to low if solar and DC-DC was being used at the same time. I would also look at using lower gauge wire on the output of bot of those units.

good point! I will upgrade that to 6 AWG and use a at 75A fuse at the bus bar

You don't show a fuse of breaker from bus bar to fuse block, you are changing wire size from 2/0 awg to 8 awg. This is a good place for a switchable breaker.

Hmmm, looks like I was blindly keeping things the way Sportsmobile originally wired them (no protection at source, 40A breaker at fusebox). I'll add a 40A manual breaker at the bus bar.

Trickle charge from the Victron Multiplus is always on, I would expect some feedback from DC-DC to cause issues.

You got me to do a bunch more reading.... Looks like the Victron "trickle charger" is pretty dumb, and specifically has no extra smarts for charging a lead acid starter battery using a LiFePO4 house battery.

This page has the best definitive info: How does the Multiplus trickle charger work Also, a popular youtube video ("Victron MultiPlus Compact Battery Charger/Inverter INSTALL, WIRING & REVIEW") shows dangerously incorrect wiring for this trickle charger. After watching that video, I copied their mistake in my wiring!

In any case, I will just delete this trickle charger feature.

Solar needs a dual disconnect switch (switches ground & power at the same time). Especially if having a 80 volt input. It is also a code issue.

So I don't shock myself while working on the system on a sunny day? Somehow I hadn't thought of that. Good idea!

 

[geoffff]

Updated schematic:

 

[Stormy98]

The way to think about it is:

1) How much current will the wires carry? Then size appropriately.

2) What size fuse or breaker is needed to protect the wire?

For example, the Victron inverter will nominally draw around 2000va/12v = 167 amps. The DC loads could add another 50-100 amps. It's unlikely everything would be running at once but it's good to be prepared. And brief output peaks from the Muliplus could drive the amps higher.

So it might be worth it to upgrade the battery wire to 3/0 or even 4/0. It serves to future proof it a bit too in case you add capacity later.

Then, for the fuse, typically add 25% to the current rating for the wire. But that leads me to a question for Scalf77: The ABYC tables say 2/0 can handle 330 amps if rated at 105C. If that's the case, would a 400 amp fuse be appropriate?

 

[Scalf77]

Thanks again for the detailed advice! I'm learning as I go here, and it's sometimes hard to realize how much I don't know yet.


I'll switch to 200A fuse to match house battery max output amps: 200A


House battery is limited to 200A output. Starter battery can produce far more. I'll put a 200A fuse at starter battery end of this cable. I know this is a bit edgy for 2 AWG cable, but it allows for emergency start.

My Sportsmobile originally came with no fuse for this 2 AWG cable. I have already experienced an engine fire because of it!


These chargers can only produce 30A + 35A. So, isn't the bus bar itself the real "source" as it can produce far more current than the chargers, at 200A?


good point! I will upgrade that to 6 AWG and use a at 75A fuse at the bus bar


Hmmm, looks like I was blindly keeping things the way Sportsmobile originally wired them (no protection at source, 40A breaker at fusebox). I'll add a 40A manual breaker at the bus bar.


You got me to do a bunch more reading.... Looks like the Victron "trickle charger" is pretty dumb, and specifically has no extra smarts for charging a lead acid starter battery using a LiFePO4 house battery.

This page has the best definitive info: How does the Multiplus trickle charger work Also, a popular youtube video ("Victron MultiPlus Compact Battery Charger/Inverter INSTALL, WIRING & REVIEW") shows dangerously incorrect wiring for this trickle charger. After watching that video, I copied their mistake in my wiring!

In any case, I will just delete this trickle charger feature.


So I don't shock myself while working on the system on a sunny day? Somehow I hadn't thought of that. Good idea!

So for the most part is best practice to fuse the source of any device giving power. The manuals of each device almost always recommend an output fuse. In most cases if you have kept the wire length short, it will provide protection on the other side. If you have a long run or one that goes through metal or something else you are not comfortable with you can add a fuse at the other end. I would individually fuse each device and go directly to the main bus bar, no intermediate bus bar in most cases.

Agree, working on a van now that has about 14 foot of wire that goes through the floor twice, through a switch and then to goes to their circuit breaker before the input of the fuse panel.

I use the victron trickle charge as a third option for charging via a switch. (That means it works but don't use it). I also don't run a DC-DC charger, but you would need to isolate or isolate the input of the charger ( you should be able to disable the victron). This is also needed for other methods of charging the start battery.

The way to think about it is:

1) How much current will the wires carry? Then size appropriately.

2) What size fuse or breaker is needed to protect the wire?

For example, the Victron inverter will nominally draw around 2000va/12v = 167 amps. The DC loads could add another 50-100 amps. It's unlikely everything would be running at once but it's good to be prepared. And brief output peaks from the Muliplus could drive the amps higher.

So it might be worth it to upgrade the battery wire to 3/0 or even 4/0. It serves to future proof it a bit too in case you add capacity later.

Then, for the fuse, typically add 25% to the current rating for the wire. But that leads me to a question for Scalf77: The ABYC tables say 2/0 can handle 330 amps if rated at 105C. If that's the case, would a 400 amp fuse be appropriate?

For sizing you would need to look at worst case not nominal, so for your above calculation it is not 12 volts but instead the low voltage cutout of the device or with lithium the low voltage cutout of the BMS. I generally use the default setting for low voltage cutout of the device, unless I am setting it lower for some reason or the listed operating voltage of the device. Also you need to take into account the efficiency of the product , so at full load it might be 80% so that puts you at 2400/10.5 = 228 .

I would say the fuse should be below the wire size, my general take is that it is high enough to not induce intermittent hits. Being that many times, the wire size is driven by voltage drop not just ampacity. I would look for a fuse or breaker size between my worst case number and ampacity number. I would not say that typical fusing is recommend to be 25% above wire size, that would be more of a worst case.

 

[Stormy98]

Thank you Scalf77, I wrote my post too fast and you're absolutely right. The 125% fuse calculation should be based on the expected current draw and not the wire size. The fuse rating should be under the wire rating so the fuse goes before the wire goes.

To continue the above example, if the inverter was pulling 228 amps and say there was another 50 amps in DC loads, that would give 278 amps on the wire. 2/0 cable at 105c is rated 330 amps so that would be edgy but good, right? And a good fuse in this case would be 300 amps - enough to leave a little headroom for additional current but below the wire rating. And, really, in this scenario upgrading to 4/0 cable and using a 350 amp fuse would be best. Am I thinking about this correctly now?

 

[geoffff]

The only reason why I have two bus bars in my design, is that I don't have room for all the devices in the same place under the rear seat. Some are going to the left of the center fresh water tank, some to the right -- and so each side gets a bus bar -- unless I run multiple connecting wires, which I suppose I could.

 

[geoffff]

Solar needs a dual disconnect switch (switches ground & power at the same time). Especially if having a 80 volt input. It is also a code issue.

That dual disconnect switch you linked to is HUGE!




A friend recommended I go with this DC breaker instead.

 

[Scalf77]

The dual DC breaker works fine also. The disconnect I have used is smaller, but I didn't see anymore I was trying to give a reference., should have looked closer to the dimensions, I apologize.

 

[drobinson-SMB]

All good feedback so far.

One more for your consideration, I'd be concerned about the emergency start curcuit exceeding your lithium battery max discharge current specification. Most lithium batteries are not rated for starting duties. Check your specific battery specifications.

As an alternative simplify the system and use a portable "jump box" like this if you kill your starting battery. You get the added benefit of being able to loan it to another person for their vehicle if you come across a stranded motorist. I've done this several times.

 

[drobinson-SMB]

Just had three other thoughts:

DC loads

• The 12v feed to the DC fuse block (existing) is coming from the inverter and is 8 AWG.
  I'd move that to the bus bar and verify it is size appropriately for your max 12v load.
• It also needs a fuse or circuit breaker appropriate for what ever size wire you run from the buss bar.

Grounding

• Can't see the negative side of your system, but verify all grounds run through the shunt to the battery.
• Probably a chassis ground will be required since SM seems to use a lot of chassis grounds in the 12v system.
• Probably need a case ground for the inverter in addition to the ground through the bus bar, check the manual.

Solar

• I don't think a fuse is required for 200w of panels, but if it is, you need two (one on each conductor)
  

 

[geoffff]

Thank you drobinson-SMB -- It looks like you're responding to my initial schematic.

I've updated it since then. (I can't go back and edit my original post.) Here is what I have at this point:

 

[geoffff]

One more for your consideration, I'd be concerned about the emergency start curcuit exceeding your lithium battery max discharge current specification. Most lithium batteries are not rated for starting duties. Check your specific battery specifications.

From what I read my BMS should automatically current-limit itself to the rated max output.

 

[1der]

From what I read my BMS should automatically current-limit itself to the rated max output.

Just to clarify - The BMS shuts the battery down completely when max discharge is reached. It does not continue providing current at a flat level.