During Lvuman's recent battery testing he discovered a problem with the 300a ANL fuses he used just off his battery terminals. He observed that within just minutes of running the air conditioner the ANL fuse temperature shot up to 200° and a very acrid hot/burning smell was apparent. In fact Lvuman told me at the time that it was so hot, he couldn't hold a finger on the cable next to the lug and the heat smell was oppressive. He had to wait for the ceiling fans to exhaust the air before he could go back inside the motorhome because it was irritating his lungs. This issue only became apparent when he began his single battery test. This was probably because the air conditioner amp draw off a single battery was 177a when the air conditioner compressor was running. It wasn't obvious when using his 3 batteries because the amp draw is divided among the three batteries, at around 60a per battery. The ANL fuse temperature of each battery was 120°, 120°, and 147°. High, but not out of normal operating range. Lvuman tested all the batteries running the air conditioner one at a time to confirm if they all exhibited the high temperature issues, which they did. After testing the fuses on all the batteries, replacing one, and retesting, it was decided to just remove the ANL fuse on the one battery and see how the system operated. He then tried the air conditioner test again. This time everything worked as it should and temperatures among connections and the battery BMS were all monitored, with the highest connector temperature of around 105° and a BMS temperature of 152°. Once Lvuman finished his test he wrote up his ANL fuse issue, testing data, and provided it to Lithionics so we could start troubleshooting the issue with them. Lithionics said the BMS temperature should not exceed 160°. They also said, under a 180A load, the fuse assembly temperature should not have exceeded about 170°. So they were very curious to understand why the ANL fuse got so hot.
While there is nothing wrong with using ANL or MRB Terminal fuses, you must ensure that they are well designed products meant to be used in Marine and RV battery applications. Lithionics recommends Blue Sea or Victron products. Lvuman got his ANL fuse from Windy Nation,
https://www.windynation.com/ANL-Fus...L-Fuse-Holder-with-ANL-Fuse/-/1659?p=YzE9Ng==. He connected them to each of his batteries using a copper bus bar which connected to the battery terminal on one side and the ANL fuse on the other. They were as close as possible to the battery, as Lithionics recommends (within 7 inches).
It is important to recognize that fuses work by melting a metal link to break the electrical connection when they exceed their amperage rating, so they do get very hot when operating close to rated amperage. Also, it is important to understand that when 12vdc connections aren't properly made or electrical components like fuses aren't made of high quality copper or even better nickel or tin plated copper, then resistance builds, which causes heat, which in turn causes a voltage drop. Lvuman saw over a 1 volt drop from the battery voltage reading to the inverter 12vdc terminal voltage readings. When you smell a hot/burn smell and know your operation isn't close to the amperage rating, you can only assume the connections are now getting weaker, thus yielding more resistance, generating more heat and dropping in voltage. Basically your 12vdc electrical system enters a failure spiral, building more and more resistance and heat generation, until something has to give; hopefully the fuse blows and/or the holder only melts, before anything worse happens.
So always check the specs on your fuses, because most fuses can handle double their current draw for a brief time. If you aren't using BlueSea or Victron products then make sure you are buying equivalent material and specification items. Also, check all your 12vdc cable connections and fuses by taking temperatures and voltage readings post-installation, pre-powerup and during initial testing to identify any resistance, hot spots or voltage drops. If there is, you need to pinpoint the problem and remove it, or replace the fuse. An easy way to do this is to probe your battery positive to battery negative and see what voltage you have. Next, probe the battery negative to various points along your fuse and fuse holder. If you get anything lower than the previous voltage, you have resistance! Do this systematically along your connections, from the battery to the inverter.
Besides poor quality material fuses, having washers or heat shrink where they don't belong will also increase resistance and generate heat. It is interesting that Windy Nation shows a flat washer in between the cable lug and their ANL fuse, Figure 2. This is a big No No! You NEVER want a washer or heat shrink in between the connectors and/or Fuse/Fuse Holder. If you are stacking connectors on a terminal, again, you don't want a washer or heat shrink in between the connectors. They also show the ANL fuse attached directly to the battery, which again is a very bad practice. Figure 3 shows the proper way. Also stack your connectors in a Christmas tree fashion, the largest sized lugs or cable connectors at the bottom decreasing in size to the smallest on top.
Lvuman verified that all his connections were properly made and tight. He included pictures of his ANL fuse/fuse block connections so Lithionics could see how he installed them.
As with anything, the devil is in details and we needed to analyze the data before jumping to conclusions. The goal is to find a spot with relatively high resistance, where most heat is generated. Resistance creates voltage drop, so look for it with Digital Voltage Meter (DVM). Lithionics advised Lvuman to use a DMV in the mV range and try to find out where most of the voltage drop occurs while under load, measuring at different points starting from battery terminal, on the fuse assembly and to cable lug after the fuse assembly. They wanted him to measure mV drops between all adjacent points marked in Figure 1, while under steady load. On at least 2 fuse assemblies, ideally all 3 battery fuses, if they can be reached, so you can correlate temperature rise with voltage drops (Figure 1). Finding where the voltage drop starts will point to the source of heat. They didn't need the voltage tested under 180A load, no need to create extreme overheating again. Even at typical 60A draw you should see measurable values, enough to compare with some baseline. To pass high current from lug to lug or lug to fuse, you have to maximize surface contact area, so washers or nuts or bushings which press 2 contact surfaces together must themselves have a large enough diameter to create an adequate surface area of compression. Lithionics also advised that the problem could be poor contact between fuse and the cable lug.
After a volley of emails, one of the Lithionics Engineers wrote something I thought was particularly informative; there are quite a few factors that go into selecting the correct fuse but to address the immediate issues I want to go over a few things. It was never specified in the Lithionics manuals to install ANL fuses directly to the battery post, MRB Terminal fuses yes, but not ANL. MRB Terminal fuses are designed to be attached directly to the battery post whereas ANL fuse holders are not. The ANL fuse and fuse holder specified in the manual are from a company that has a reputation for quality and tested products (Blue Sea or Victron). The Blue Sea fuse block is rated to 750 amps and is designed to handle the heat that may be encountered when running high currents. The ANL fuse block should be mounted as close to the battery as possible (within 7 inches). It should be noted that the ANL fuse itself should never be connected directly to the battery terminal, a fuse block/holder must always be used. If the conductor is contained within a sheath or enclosure (conduit, junction box or enclosed panel) the fuse can be placed as close as practical to the battery but should not exceed 72 inches. Below is an image of the specified fuse block, as you can see it has large conductive surfaces where the fuse is attached and can handle up to 4/0 cable. While ANL fuses should typically not be a problem, a specific installation at the battery terminal might be better off using MRB Terminal fuses (Figure 5), purely due to mechanical design and shape of the assembly.
More from information from Lithionics; Stainless or carbon steel nuts used as risers or spacers will also have a negative impact in many ways (resistance, heat rise, or lack of heat sinking). When using the Blue Sea ANL fuses they do need to be used with the corresponding Blue Sea ANL fuse holders, not used directly on a terminal as the Windy Nation pictorial shows. The same for Class J or T Fuses. The MRB Terminal Fuse Holder is the only one designed for direct attachment to a battery terminal. Another detail that did not make sense, it appears the Windy Nation ANL fuses themselves are made of brass or brass plated.
Lvuman did more research and realized that the Blue Sea ANL fuses are made of copper and plated with Nickel, which is better than just plain copper because it greatly reduces oxidation. Oxidation adds resistance over time. It should be noted that Brass is only 28 percent copper, so if a fuse is made of brass or brass plated, you are losing 2/3 of your IACS (internal annealed copper standard) rating. Based on this information Lvuman was able to determine that the ANL fuses he installed from Windy Nation were a big mistake! The fuse block that came with the Windy Nation 300 amp ANL fuse is clearly not rated for high amperage and the fuse, upon closer examination certainly looks like it's made of brass or brass plated. There is evidence on the bottom of the fuse block that it was starting to melt. Lvuman decided to go with the Blue Sea terminal fuse block and a Blue Sea 300a terminal fuse. He just installed them, one on each battery, and will be testing them this week. He told me he learned a lot from his exchanges with Lithionics and now he is not at all surprised by the issues he encountered with the cheap Windy Nation ANL fuses. He told me, "Quite an education! I'm very eager to try the Blue Sea Terminal fuses. This looks like a case of “you get what you pay for! A Quick search for genuine Blue Sea products shows approximately. $60 for one ANL fuse and one holder, while Windy Nation shows $16 for 2 fuses and one holder. These brass fuses and plastic holders are obviously cheap knockoffs, so no surprise with the end results. This experience was a great lesson learned!"