H38: What is this Xantrax device under my main DC panel

[flightlead404]

I'm in the process of expanding my 6 month old 400AHr LiFePO4 house bank to 600AHr by adding an additional battery in parallel in between the current two.

In tracing the cables to be sure I understood how everything was put together, I discovered this item wired in the battery positive cables between the house battery main switch BATT terminal and the two cables from the positive terminals of the existing batteries. It is practically inaccessible, they must have build the boat around it. I can only feel it with fingertips, so have zero hope of changing any cabling to it, or even getting eyes on it. I took these pics by holding my phone under the cabin sole.

What is it? Is it simply a large terminal block? It looks like there may be a fuse of some kind in there, but zero hope of ever changing it out.

FWIW my current set up is a 4D under the cabin sole right by this, a more or less empty under settee storage forward where my charger is located, and then another 4D in another under settee storage forward of that. Currently the most forward battery has a single 2/0 cable from the positive terminal back to this Xantrax object, and two negative 2/0 cables, one which runs to the main boat DC ground via a shunt for the battery monitor, and another which runs to the negative terminal of the aft battery under the cabin sole.

My plan is to mount the new battery midpoint in the mostly unoccupied space along with the charger, move the positive and non-shunt negative cables from the current forward battery to the new midpoint battery, and install two new 2/0 cables from the new midpoint battery terminals to the existing forward battery.

 

[rgranger]

Can you push this cable out of the way and retake the pic?

I'm wondering if a part number or serial number might be there?

There website shows a lot of power conversion/transfer products.

Do you have an inverter? One of the products that Xantrex offers is an inline transfer relay that allows switching between shorepower and inverter AC.

 

[Davidasailor26]

The round bit in the middle and the 350A marking make me think it’s a fuse like this - Xantrex 350 Amp Fuse Block and Holder - TFB350

If that’s the case and the fuse is really that inaccessible that’s not ideal. Could certainly be annoying if it blows and you need to replace it to get the whole house system working again.

 

[Richard19068]

Xantrex Battery Fuse & Holder 350A Battery Fuse Kit/TFB350 RV/Marine/Commercial | eBay

Model: TFB350. Xantrex 350 Amp Battery Fuse Kit TFB350. USED XANTREX BATTERY FUSE. As current passes through any cable, heat is generated. If the inverter draws more current than the cable can handle due to heavy loads, excessive heat is produced.

www.ebay.com

 

[mermike]

Yep, a Class T fuse and fuse block.

 

[flightlead404]

Can you push this cable out of the way and retake the pic?
View attachment 218959

I'm wondering if a part number or serial number might be there?

There website shows a lot of power conversion/transfer products.

Do you have an inverter? One of the products that Xantrex offers is an inline transfer relay that allows switching between shorepower and inverter AC.

Not easily. p/n is on the other end however, and I can't get a focus on it. I have an inverter but not xantrax, not factory installed, and no auto xfer function.

 

[flightlead404]

The round bit in the middle and the 350A marking make me think it’s a fuse like this - Xantrex 350 Amp Fuse Block and Holder - TFB350

If that’s the case and the fuse is really that inaccessible that’s not ideal. Could certainly be annoying if it blows and you need to replace it to get the whole house system working again.

thanks

Yes I agree. I may have another go at it, but wow what pain.

 

[mermike]

Could certainly be annoying if it blows and you need to replace it to get the whole house system working again.

 

[flightlead404]

Xantrex Battery Fuse & Holder 350A Battery Fuse Kit/TFB350 RV/Marine/Commercial | eBay

Model: TFB350. Xantrex 350 Amp Battery Fuse Kit TFB350. USED XANTREX BATTERY FUSE. As current passes through any cable, heat is generated. If the inverter draws more current than the cable can handle due to heavy loads, excessive heat is produced.

www.ebay.com

Yep that looks like it. Thanks.

so as far as I can tell, one end of the fuse connects to the BAT post on the main house bank switch, the other end is connected to both positive terminals of the two existing batteries.

 

[Davidasailor26]

Yep that looks like it. Thanks.

so as far as I can tell, one end of the fuse connects to the BAT post on the main house bank switch, the other end is connected to both positive terminals of the two existing batteries.

Makes sense - that would be about the right place for a fuse. Ideally it should be within 7” of the battery terminals.

 

[dlochner]

My plan is to mount the new battery midpoint in the mostly unoccupied space along with the charger, move the positive and non-shunt negative cables from the current forward battery to the new midpoint battery, and install two new 2/0 cables from the new midpoint battery terminals to the existing forward battery.

I'm confused by this. Installing additional batteries is not just about finding space for them, it is to ensure the cabling is correct. Can you draw a schematic of the current cabling and a schematic of the proposed cabling.

 

[flightlead404]

I'm confused by this. Installing additional batteries is not just about finding space for them, it is to ensure the cabling is correct. Can you draw a schematic of the current cabling and a schematic of the proposed cabling.

Yes that was the whole point of the exercise.

 

[dlochner]

Yes that was the whole point of the exercise.

There are a few issues with your plan.

When paralleling batteries or putting them in series the connecting cables must of the same length otherwise the batteries will not be charged evenly.

You don't show where and how you will charge the batteries, this matters.

If the plan is to fully isolate the bow thruster battery, that battery should be independent of the house batteries. It can be charged by using an ACR, Argofet, or battery to battery charger. As you have it drawn the third battery is not really in parallel with the other two. A properly paralleled battery bank will have all the batteries acting as one, so that the current draw is spread across all the batteries. as you have it drawn the current will be drawn unevenly.

If you are adding a LFP battery to the mix, it too will need a Class T fuse. It will also need to have a high discharge capacity because of the initial draw of the thruster. You will probably need a LFP battery with a max short term discharge capacity in excess of 300 amps.

A LFP battery is not necessarily the best choice for a thruster battery. The bow thruster will use a lot of current for a short period of time, but never be deeply discharged. A good quality AGM battery would be a better choice as they can easily provide the high current the thruster will require and will only be subject to shallow discharges which the charging system can easily and quickly handle using a DC-DC charger.

 

[flightlead404]

There are a few issues with your plan.

When paralleling batteries or putting them in series the connecting cables must of the same length otherwise the batteries will not be charged evenly.

You don't show where and how you will charge the batteries, this matters.

If the plan is to fully isolate the bow thruster battery, that battery should be independent of the house batteries. It can be charged by using an ACR, Argofet, or battery to battery charger. As you have it drawn the third battery is not really in parallel with the other two. A properly paralleled battery bank will have all the batteries acting as one, so that the current draw is spread across all the batteries. as you have it drawn the current will be drawn unevenly.

If you are adding a LFP battery to the mix, it too will need a Class T fuse. It will also need to have a high discharge capacity because of the initial draw of the thruster. You will probably need a LFP battery with a max short term discharge capacity in excess of 300 amps.

A LFP battery is not necessarily the best choice for a thruster battery. The bow thruster will use a lot of current for a short period of time, but never be deeply discharged. A good quality AGM battery would be a better choice as they can easily provide the high current the thruster will require and will only be subject to shallow discharges which the charging system can easily and quickly handle using a DC-DC charger.

The cables are all 2/0 AWG. The cables running to the forward battery are probably 10'. I was planning on adding 2/0 6' cables between the mid-point battery and the forward battery. I can check the voltage drop over 4' of 2/0 cable (the difference), but do you think it is significant? Pretty sure I had previously checked this and determined it wasn't, but I have not built these cables yet and its easy to change.

The main battery charger connects via the COM post on the battery switch, as does the DC-DC charger from the alternator, both via suitably sized panel-mounted breakers. This will not change. This is stock other than the DC-DC charger replaced a relay that was energized by the ignition switch when in the RUN position. Now charging starts on an input voltage threshold.

There are no plans to change anything wrt the bow thruster. The bow thruster connection is stock, and functions perfectly as set up. The measured in-rush and steady state current are well within the capacities of the battery BMS.

What makes you say the current will be drawn unevenly? Because the bow thruster positive terminates on the 1st battery and not on the DC panel switch? This is the stock setup. I tried to relocate it to the DC panel, but its physically a challenge due to limited room behind the panel and cable thickness/bend radius. The difference is probably 18" of 2/0 AWG.

All three of these batteries are identical 200 AHr LiFePO4.

The other alternative is to connect it to my start battery directly. I originally tried to do this when I went LiFePO4 6 months ago, can't remember off hand why I did not. FWIW my windlass is connected to the start battery via a separate post on the DC panel.

 

[rgranger]

Yep that looks like it. Thanks.

so as far as I can tell, one end of the fuse connects to the BAT post on the main house bank switch, the other end is connected to both positive terminals of the two existing batteries.

WoW! What a PITA. What good is a fuse if you can't access it? Is there any place you could install something like this (see pics)? Then if you ever needed to change the fuse .... Maybe it is lucky you found this now before you needed to know about it.

 

[dlochner]

What you are describing is not what you have drawn, making it difficult to give you advice because the problem keeps changing.

In a proper parallel battery bank, the electron flow is from one battery to the next and so on until it leaves the bank. In your arrangement the electrons flow from 2 sources which means the draw will be uneven, some electrons will flow from the single battery and some from the 2 battery bank. The current draw will be even across the 2 bank, thus if you have a 100 amp draw, 50 amps will come from the single battery and 50 amps from the 2 battery bank. However, each battery in the 2 battery bank will contribute just 25 amps. After 2 hours the first battery will be at 0% SOC and the other 2 batteries will be at 50% SOC.

You will also run into issues with charging, as the more deleted bank will not be done charging when the 2 battery bank will be done. The BMS maybe able to handle this, I'm not certain. Once the first battery is depleted the other 2 batteries will start to discharge into the depleted battery.

In a proper parallel system, at the end of the 2 hours at 100a, all three batteries will be at 67% SOC, they will be balanced and will be charging at the same rate, the cycles will also be even. All this is boat electrical system 101.

As for the cable size and length, at low current draws on a large cable, like 2/0, there is negligible voltage drop, however as the current draw increases the voltage drop increases. So uneven charging and discharging occurs with cables of different lengths between batteries.

 

[flightlead404]

What you are describing is not what you have drawn, making it difficult to give you advice because the problem keeps changing.

In a proper parallel battery bank, the electron flow is from one battery to the next and so on until it leaves the bank. In your arrangement the electrons flow from 2 sources which means the draw will be uneven, some electrons will flow from the single battery and some from the 2 battery bank. The current draw will be even across the 2 bank, thus if you have a 100 amp draw, 50 amps will come from the single battery and 50 amps from the 2 battery bank. However, each battery in the 2 battery bank will contribute just 25 amps. After 2 hours the first battery will be at 0% SOC and the other 2 batteries will be at 50% SOC.

You will also run into issues with charging, as the more deleted bank will not be done charging when the 2 battery bank will be done. The BMS maybe able to handle this, I'm not certain. Once the first battery is depleted the other 2 batteries will start to discharge into the depleted battery.

In a proper parallel system, at the end of the 2 hours at 100a, all three batteries will be at 67% SOC, they will be balanced and will be charging at the same rate, the cycles will also be even. All this is boat electrical system 101.

As for the cable size and length, at low current draws on a large cable, like 2/0, there is negligible voltage drop, however as the current draw increases the voltage drop increases. So uneven charging and discharging occurs with cables of different lengths between batteries.

I'm unclear what you are saying. (I know my drawing is crap lol)

The boat ground is from the negative terminal of one end of the battery bank (most forward end), the positive is the positive terminal of the other end of the batter bank (near DC panel). The batteries are jumpered, post to post, with 2/0 AWG. Don't let the junctions as drawn confuse you, all the jumping is to the battery post. The one exception is that the middle battery and first battery positive jumpers which both terminate on the Class T fuse block rather than the middle battery positive jumper going to the battery post of the first battery.

Are you saying that the 18" of 2/0 AWG between the first battery post and the Class T fuse is electrically significant?

All loads, with the exception of the bow thruster come off the DC panel via the Xantrax Class T fuse. The bow thruster (which has its own suitably sized ANL fuse not drawn) is connected to the first battery positive post. But again, isn't this a question of 'is 18" of 2/0 AWG electrically significant'?

All charging comes from the DC panel, via the Class T fuse. So again, isn't this a question of 'is 18" of 2/0 AWG electrically significant'?

As far as I can tell, the only difference between the ideal setup and what I have is that the positive jumper from the middle battery to the first battery terminates on the Class T fuse, rather than on the positive post of the first battery itself. AFAICT it all boils down to 'is 18" of 2/0 AWG significant enough to make any real-world difference'?

For a 300A load at 13.5V:
Voltage drop: 0.091
Voltage drop percentage: 0.67%
Voltage at the end: 13.409

EDIT: My guesstimate at 18" is from memory, and thinking about the ABYC standards and the ISO/RCD standards of 7", it could be less than 18" if Hunter tried to be compliant in 2007.

 

[Davidasailor26]

Don't let the junctions as drawn confuse you, all the jumping is to the battery post. The one exception is that the middle battery and first battery positive jumpers which both terminate on the Class T fuse block rather than the middle battery positive jumper going to the battery post of the first battery.

Having the middle battery jump straight to the fuse is the concern. Only the first battery should go to the fuse, if the last battery is the one getting the negative. If you jump from the middle battery to the fuse the first battery will get just a little less wear than the middle and last. As you point out the voltage drop along that extra cable isn’t that bad, but considering lithium’s very flat discharge curve even that low voltage drop could make a difference in the long term.

In a proper parallel battery bank, the electron flow is from one battery to the next and so on until it leaves the bank.

Just to nitpick - a parallel bank could also have each battery feeding single positive and negative bus bars directly. As long as the cables to the busses are equal I think that’s also generally accepted.

 

[flightlead404]

Having the middle battery jump straight to the fuse is the concern. Only the first battery should go to the fuse, if the last battery is the one getting the negative. If you jump from the middle battery to the fuse the first battery will get just a little less wear than the middle and last. As you point out the voltage drop along that extra cable isn’t that bad, but considering lithium’s very flat discharge curve even that low voltage drop could make a difference in the long term.



Just to nitpick - a parallel bank could also have each battery feeding single positive and negative bus bars directly. As long as the cables to the busses are equal I think that’s also generally accepted.

As my old Dad used to say to me "In theory, theory and practice are the same. In practice, they rarely are." Given the pretty minute voltage drop over a few inches of 2/0 cable, I don't think there is a practical difference. But, I'm open to a quantitative argument otherwise.

Yes, there might be a tiny difference in the wear of each battery, but significant enough to make a real-world difference? Especially since this is LiFePO4 with a BMS in each battery?

 

[Stu Jackson]

Same skipper, different forum: Fuses needed on each battery in a bank? - Cruisers & Sailing Forums