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Frequently Asked Questions (FAQ) — Auto-Cutoff ModulesThis FAQ answers the following questions:
Are CamLight Systems' Auto-Cutoff Modules (ACMs) hardened for use in a fighting robot? No. Although it is durable, it is not designed to handle the tremendous g-forces it would experience during a fight. Go to top Can I discharge more than one pack at a time with an ACM? We don't recommend discharging NiCd or NiMH packs in parallel. Some users have had no problem discharging multiple packs this way, but one or more cells can potentially be damaged. You can use multiple loads without problems, as long as the combined load current doesn't exceed the continuous discharge current rating. Go to top Can I discharge my 36V packs with an ACM? Unfortunately, no. ACMs are rated for use with up to 24V (20-cell) packs, with an absolute maximum of 35V. Do not use ACMs with battery packs containing more than 20-cells. Even 24V (20-cell) packs can be at up to 32V or so immediately after charging. You can discharge 36V packs with our PD-36V Pack Discharger though. For more information, see the Pack Dischargers page. Go to top Can I use multiple ACMs to discharge one pack? Yes. If you need to exceed a single ACM's continuous current or surge current rating, you can parallel ACMs. Be sure that the loads on any one ACM do not exceed its rating or the ACM will shut down to protect itself before the discharge is complete. During a discharge, one ACM may turn off a short time before the other(s). This is normal and is due to the small differences in the cutoff voltages between ACMs. Go to top How much can I safely exceed the max. continuous current rating if I'm not discharging for a long time, i.e., not continuously? Officially, not one bit. OK, with that out of the way, here's the scoop. The ACMs are conservatively rated to ensure a long, trouble-free life. You can exceed the ratings, but that can shorten the life of the ACM, perhaps considerably. Electronics hate heat. Even though the ACM-40F and ACM-15 are protected from over-temperature and over-current conditions, repeatedly causing the ACM to shut down to protect itself can cause it to stay at a very high temperature for long enough to damage the MOSFETs. This damage is cumulative and can eventually cause the MOSFETs to fail. If you're discharging 3AH (or lesser capacity) battery packs, you can occasionally exceed the max. continuous current rating of either ACM without problem. If the ACM turns off before a discharge is complete, due to an over-current or over-temperature condition, do not continue discharging at that rate! Please contact us about your setup and we'll help you get the most out of your ACM. Go to top I accidentally shorted out the load connections (or exceeded the max. surge or continuous current rating) during a discharge and I couldn't restart my ACM-40F or ACM-15. What's wrong? After a short-circuit, over-current, surge current, or over-temperature (>175º C.) condition, the ACM shuts down and needs to be reset before continuing the discharge. This is done by by disconnecting the battery pack and load, making sure the load is within the ACM's ratings (or the short circuit has been repaired) and properly re-connected, and then reconnecting the battery pack. You can now continue the discharge by pressing the Start button again. Go to top I used several large motors (or bulbs) as a load for my ACM and nothing happened (or I only get a "blip") when I pressed the Start button. What's wrong? The protection circuitry of the ACM-40F and ACM-15 will turn everything off within microseconds if the surge current rating is exceeded (see the Auto-Cutoff Modules page for these ratings). Motors and bulbs have a very large starting current and several used together can exceed the surge current ratings of the ACMs. To prevent this you can use additional ACMs in parallel, fewer motors or bulbs, substitute a different type of load, or use an inrush current limiter (ICL) to suppress these large surge currents. We've successfully used the Thermometrics Model CL-101 Inrush Current Limiter (16A max., steady-state), available from DigiKey (part #KC024L-ND) and other sources. Be aware that ICLs can get very hot, up to 175º C., during normal use. Before using this ICL, or any other, be sure to download its data sheet and fully understand how to properly and safely specify, install, and use an inrush current limiter in your application. Do not use an ICL unless you've taken all proper precautions. Go to top Why do I have to hold down the Start button for a couple of seconds when using large incandescent bulb or motor loads? The large starting (surge) currents that these loads draw when powered up can cause the battery pack to drop below the cutoff voltage. The Auto-Cutoff Module (ACM) senses this and turns off when you release the Start button. If you hold down the Start button until the bulbs are at full brightness or the motors are up to speed, the battery pack's voltage will rise back up and the ACM will stay on when you release the button. If this doesn't work, and you're sure the battery pack isn't already discharged, you'll need to reduce the load or add inrush current limiters. Go to top For more information on discharging NiCd/NiMH packs, see our
Why Discharge? and
Tech Tips pages
Home Page · Pack Dischargers · Auto-Cutoff Modules · Load Modules · Accessories & Parts · Custom ProductsCopyright © 2003-2008 John Muchow. All rights reserved. |