T-Fuse and Battery cut off switch warm/hot

yantruocmot

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Feb 12, 2022
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I have just installed my first system so this is a sanity check. I understand a lot technically and mechanically about the systems and why different components are used and wire sizing etc. which I know prob makes me dangerous at this point. The system works, and works great, I am however confused at one thing that I am experiencing. Unfortunately I don't have a current diagram but I will try and explain.

My system is 12v, I have a Xantrex 2000w inverter, Victron Shunt, Lynx Power In, and 100/50 smart MPPT, and 300ah (soon to be 400ah) of LiFePO4 battery.
I have the lynx power in converted to allow for fuses on the output/input side (4 connector side) like a lynx distro has and I have fuses there for the inverter connection that is 4/0 cable and fuses for the 12v to the PowerCenter. I connected my battery input on its main side connection of the power in.

The path the electricity has to run from battery is this.

Positive connection:
  1. The lynx is directly connected (via bolt/nut) to a seaflo battery switch (https://www.seaflo.us/product/batte...id=fb6698fccd3d11eca52beb764e977f4b#undefined)
  2. The switch then connects to a blue sea 250amp T Fuse via a 6" 4/0 wire, this is in a blue-sea t-fuse holder/mount with cover
  3. From the fuse it then goes down to my battery positive connection via 4/0 cable.
Negative connection:
  1. The neg side of the lynx in connects to a Victron shunt via a 6" 4/0 cable
  2. The shunt is then connected to the battery via 4/0 cable
I have 3 100ah batteries connected in parallel, I connect those to each other via 1/0 cable, it always stays cool at each connection.

All wires stay cool maybe slightly warm (but I am in AZ and its already over 100 so might just be ambient temps). But the fuse and the battery disconnect get hot. Not crazy hot or glowing red. I believe they should stay cool from what I have read. I have checked all connections and they are tight, I am afraid to crank down on them as I dont want to break the fuse holder etc... How tight should they be, is there a specific torque?

Now to be clear, this only happens when I run the AC for a while, i.e. 1hr or more (yes the 2000w inverter runs the 14500btu Furrion AC just fine with its micro-air softstart, just cannot run any other AC item at the same time). Running the microwave or a hairdryer does not cause this, but they do get warm on those. Everything else works fine, the transfer switch on the inverter seamlessly switches between invert and 120 shore power when plugged in. When plugged in to shore the batteries charge via the power center just fine, no loops or grounding issues etc.. I have just this one concern.

Is this normal? What am I missing or should I possibly replace something?
 

STW

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I just replaced a battery cable that looked fine, but was internally corroded. I cut the wire in half and saw the corrosion. Made a new cable and all good now.
 

Alice2021

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Oct 12, 2021
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Obviously, when you use high-power appliance,such as your said 14500btu Furrion AC,the cables will be hot,because the current is high. When you use low-power appliances, the cables will not heat up. If you are worried, I suggest you change a pair of thicker cables
 

Horsefly

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Your cable sizes sound sufficient, and your weekend order is good. I would be suspicious of your connections. Either the terminals or the crimps. Heat is caused by the current running through higher resistance, which can't be the wire or fuse.
 

yantruocmot

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Feb 12, 2022
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Thanks, I think it might be the connection made between the lynx and the battery disconnect, I am not 100% sure how much metal to metal is going on there. It is just going to suck to take it down to check it :( I have an infrared temp sensor I will check each connection with.
 

yantruocmot

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I just found this on another thread, I wonder if I need to get a 300amp fuse and maybe that is the problem? Again the fuse and battery disconnect (not wire between them) get very warm/hot, not burning hot. The fuse has never blown. So maybe two potential issues, the fuse is undersized and the battery disconnect might need better connection?

Using this equation, I think I need a 300amp vs the 250 that I have currently, anyone able to confirm?
2000 ac watts / .85 conversion factor / 10 volts low cutoff = ‭235.2941176470588‬ service amps.
‭235.2941176470588‬ service amps / .8 fuse headroom = ‭294.1176470588235‬ fault amps.
 

acdoctor

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Do you get the heat with full batteries 13.6 volts? Or just when the batteries are low and amperage is higher. Is the switch designed for 250 or 300 amps. The ones I have seen don’t look very robust. Dose all of the 250 amp connections have 3/8 bolts? Soldered connection or hydronic crimper should be used for those amps.
 

yantruocmot

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Feb 12, 2022
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The batteries would be full to half state of charge, have not let them get too low yet at that load so I am not sure if it will change any resistance on the load connections. The disconnect is a 300a, I specifically got this one as it was more of a name brand and the blue sea was not available at the time of purchase. I had also seen it used in other RV's from RV mfg's and such so felt it was going to be better than a amazon china knockoff.

The 1/0 cables that go between the batteries I made (crimp) and those are not even getting warm. The 4/0 cables were all purchased from BatteryCablesUSA.com and these are all also crimp. No solder was used anywhere for any connection.

All of the connections in question are 3/8 bolts (disconnect and fuse), all inside the lynx are M8 and batteries are a M8 size as well (again those all stay cool, including wires going to the inverter).
 

rickst29

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I agree that the fuse is probably being run too close to its capacity, for a reason which you didn't think of: Power Factor.

'Power Factor' is a property of Alternating Current circuits which are being used to support reactive loads (such as motors and microwave ovens). For a purely resistive load, such as a 120-VAC Toaster, Power Factor is 100% (1.0). But when the power is being used to drive a reactive load, such as the compressor and fan on your Furion AC, power factor is much less - perhaps around 75-80%.

The 'Power Factor' value of the RMS utilized watts as a proportion of the input VA (on the 120-VAC side). Xantrex "2000 watts continuous" may or may not have included a PF factor within that rating. (Victron presents those output rating separately with one of their Inverters rated "maximum RMS Power 2400 Watts / 3000 VA". Your post #6 equation uses "2000 Watts" as a VA number. It is likely that Xantrex rated the Inverter for RMS Watts, with some unknown PF value built into that rating. The Xantrex 120-VAC output has to generate the higher VA, in order to provide those Watts on the output circuit.

On the other hand, if your battery BMS units don't perform 'output shutdown' long before being pulled to 10.0 Volts, I recommend reconfiguring those BMS units. 2.5V per cell is ZERO "SOC", with one or more cells already damaged. I red-line my own "12v" battery packs at 12.0V on the pack, 3.00V on each cell - which is roughly 9.5% SOC left in reserve, with much less damage to lifespan.

My comparable equation would be:

2000 AC "watts" / .80 PF = 2500 VA.
2500 VA / .85 converter efficiency = 2941 input VA.
2941 input VA / 12.0V minimum input Voltage = 245A.
245A / .80 fuse "extra margin" = 306A.

A 300A fuse looks good, with a slightly reduced "extra" margin. The 4/0 wire is staying cool over these short shut short distances, and seems OK for this "chassis wiring" application.
 
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The batteries would be full to half state of charge, have not let them get too low yet at that load so I am not sure if it will change any resistance on the load connections. The disconnect is a 300a, I specifically got this one as it was more of a name brand and the blue sea was not available at the time of purchase. I had also seen it used in other RV's from RV mfg's and such so felt it was going to be better than a amazon china knockoff.

The 1/0 cables that go between the batteries I made (crimp) and those are not even getting warm. The 4/0 cables were all purchased from BatteryCablesUSA.com and these are all also crimp. No solder was used anywhere for any connection.

All of the connections in question are 3/8 bolts (disconnect and fuse), all inside the lynx are M8 and batteries are a M8 size as well (again those all stay cool, including wires going to the inverter).
Do you have a repeatable test case to make the fuse and disconnect switch hot?
How are you measuring the dc current?
Do you have an IR thermometer?
 

Dynoman

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Zil

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Your crimps and/or the connections are bad. Fix that!
 

rickst29

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@rickst29 power factor on the ac side would translate to ripple on the dc side, right?
That was a smart question! 120Hz ripple on the DC side of the Inverter isn't related to the kind of load being presented 120-VAC side (Power Factor), but it's almost certainly present to some degree. This would be a question regarding the effectiveness of input and output smoothing capacitors within the Xantrex.

To review for others: On the AC side, the production of 2500 VA (or any other number) approximates a sine wave curve (as closely as possible). The Voltage of the 120-VAC, 60Hz output "hot side" varies between peaks of +170V and -170V, touching each peak (and also reaching zero twice) with each of 60 cycles per second. "120 Volts" is the RMS power, not the peaks!

The output VA is varying widely, on an instantaneous basis. Unless the input smoothing is perfect (and it can't be), some "ripple" in demand will seen in the 12V current. With the highest DC current through the smoothing bridge being required at the moment of generating the 120-VAC peaks, this occurs twice per Alternating Current cycle (120 times per second).

I do not have equipment which can measure the DC current Ripple being created by my own (cheap Chinese-built) 3000/6000 Inverter, but I will SWAG that variance to be at least 20%.
 

yantruocmot

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Feb 12, 2022
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I have confirmed that the inverter is 2000w continuous can surge to 4000w. They don't list "power factor" anywhere on their spec., but from what it sounds like its the continuous output capability. Which I know Victron is lower than the number on the inverter, i.e the Multiplus 3000 is actually more of a 2500w inverter.

I have just completed a test, ran the AC set to 55deg for 1hr. At start of the test the wires and the battery disconnect terminals were all at 90 F. After 1hr they were at 110 F. Totally touchable etc..

For other info the ambient temp currently is only 76 F, yesterday when I did my first test after the bigger wire was installed the ambient temp was 100 F.

So maybe I dont really have a problem? Although I will get a bigger battery disconnect as recommended.

Here are a couple pic of the trouble area.
 

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yantruocmot

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Just ran it again for 15min, and it averaged around 90a, went as high as 100a but just for a few seconds.
 
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