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High Temperature Warning Signs

Written by William C. Shumay Jr. for Arcon Equipment Inc., published in the Material Handling Wholesaler
copyright © William C. Shumay Jr.
For more articles, please visit http://www.arconequipment.com

Because industrial electric forklifts operate at high currents and low voltages, and use electrochemical cells as a power source, it is not unusual to encounter elevated temperatures somewhere in the system. Excessive heating of components should not be ignored, however, because this indicates a problem that may get progressively worse.

Lead acid batteries heat up on charge, and they are more prone to heating as they age. Operation of batteries with internal temperatures above 80 to 90 F does age them faster, as well. Many battery manufacturers identify 110 F as a maximum for regular operation of their batteries, and identify 120+ F operation as battery abuse— which voids the warranty. This is why many charging schedules incorporate a cool-down period after charging. In multi-shift operations, spare batteries used for change-out allow the hours of cooling time considered desirable. Big batteries can take a long time to dissipate heat.

A glass thermometer can be used to measure the temperature of the battery electrolyte— an accurate reflection of the internal temperature of the cell. Cells in the center of the battery arrangement maintain the highest temperatures.

Shed that heat
Heat dissipation is important for hard-working batteries, as they gain temperature in use as well as on charge. Conventional lead-acid batteries seem to do fairly well at releasing heat by radiation from the case and connector straps and by release of water vapor from vent caps. The new sealed batteries that do not normally release water vapor do not have this heat path available, and some sealed battery designs that stack cells on their sides may have additional problems with heat dissipation.

One way that sealed batteries could compensate for heat build-up is to take advantage of the excellent thermal conductivity of copper. Sealed batteries can use copper intercell connectors— something not easily done with conventional vented batteries because of corrosion problems. Electrical insulation (necessary for safety) on these connectors, however, tends to limit the heat that they radiate.

Also, sealed battery designs generally use a "gentle" charge curve that, while it may take longer to recharge the battery, will tend to heat the battery less— at least while the battery is in good condition.

Hot Cables
Cables and connectors may get so hot that they melt insulating materials, and this is not good. Any uncomfortably warm connectors and cables need to be examined and repaired. Usually the culprit is poor contact at the tips in the connectors, or bad crimp connections. In some cases, sulfuric acid may reach the copper cable through holes in the insulation and corrode the copper. This is soon apparent by swelling of the cable. Any swollen cables must be replaced.

A word about connector tip installation: use proper crimping tools for the gauge of cable you are working with, or solder tips in place with care. The flexible, fine-strand copper cables used on batteries and chargers wick up a substantial amount of solder as they reach soldering temperature, and can "starve the joint" by removing solder that you have supplied to the tip. Be aware of this, and provide a generous amount of solder to ensure a strong joint. Big copper cables also wick away a lot of heat, so a hot torch is the way to go here. Just be careful to avoid burning or melting insulation. A non-acid soldering paste flux must be applied generously before soldering.

Be safety conscious: replacing battery cable tips when the cables are attached to the battery requires care. Work only off to the side of the battery, never over the top. If cable ends touch each other, or touch a bare connector strap on the top of the battery, a powerful electrical arc will result which can cause severe burns or ignite battery gases.

In general, hot components mean that something is interfering with clean contact between the metallic conductors, or that the overall size of the conductors is too small to carry current loads. If a charger or battery has been retrofitted with cables of a smaller than adequate gauge, then the entire cable may heat up in use. Check with the charger and battery manufacturers for their recommendations if you suspect this to be the case.

Hot Wire Check List
Hot cables or melted connectors say nothing about charger or battery output misbehavior. The problem is strictly in the cables and connectors themselves. If you encounter hot cables check the following, in order:

  1. Connector. Replace if cracked, broken, or melted. If melted, go to step 2.
  2. Check Connector contact tips for clean contact surfaces. Use no abrasives— tarnished silver surfaces are good conductors and do not need to be “brightened up”.
  3. If a lot of heating has taken place, crimped connections will be oxidized. Cut back cables to bright copper, then crimp new tips in position.
  4. Repair damaged insulation on cables properly, or replace cables. Adhesive electrical tape is not considered a safe, permanent repair.
  5. Heating near the charger end of the cables reveals a problem with the connection inside the charger. Whether from a bad terminal crimp or poorly tightened nut, heat will have oxidized copper surfaces and this oxidation must be removed before reassembly. (Unlike tarnish on silver, oxidized copper surfaces have high electrical resistance.)
  6. If the above solutions do not take care of the overheating, check cable gauge and connector current rating— make sure that they are not too light to do the job.

For more information, contact Arcon Equipment Inc. (440) 232-1422.

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