At 02:18 PM 10/28/05 -0600, Kleinbrahm, Bob wrote:
I sent an email to (EV Parts), the company that installed the Alltrax unit in a tractor that I recently purchased, to ask about the proper method of charging, see message sent to group earlier in week.The company replied with the following: The Alltrax controller you have in there is designed for an operating voltage range of 24-48 volts. The onboard charger on the tractor charges at 40 volts to be above the 36V nominal battery level, and the battery pack only draws about 15A when they're low and charging, so the controller should be OK. As a precaution, though, I recommend leaving the main manual contactor (switch) off when charging. Alltrax is primarily concerned about 48V systems where the charge voltage may be 54V or so.I interpret this to be turning the key switch off and the disconnect engaged when charging the batteries.
As someone who has been involved with the design of controllers let me jump in here with a note or two. A controller designed for a 48V lead acid system must be designed to operate up to 55V or so. It must be able to withstand (not necessarily operate) at voltages up to 60V or so. The field service agents I've worked with have seen 60V on a nominal 48V battery coming off of a 'hot charge'
On first blush this would suggest that a 36V charger on a system with a 48V controller would not be a problem, but (you knew there was a but coming didn't you) chargers tend to be noisy so a 48V charger putting out 60V into the battery will possibly have noise spikes much higher than that. A 36V charger could easily have spikes exceeding 55V. The controller will have two main weak points when presented with a charge across the DC bus, the semiconductors and the capacitors. As long as the key is off it is very possible that there is no single semiconductor across the DC bus but rather only power devices in series (forming 1/2 or 1/4 H's), If balanced these might well survive high pulses. The short high pulses that are likely to occur with a charger are not likely to immediately kill the electrolytic capacitors in the controller but they will degrade them over time.
One of the more common field service issues in the field with many brands of controllers on vehicles like forklifts is that since a lot of facilities don't properly key their battery connectors chargers get occasionally plugged into the controller side rather than the battery side when recharging. If the voltage on the caps has not decayed sufficiently the charger will attempt to charge the controller. This will sometimes blow the controller, although I don't think this was a frequent failure mode. If the capacitors holding charge has decayed then the chargers usually will refuse to start.
Bottom line is wire the charger so that the controller is not hooked up when the battery is being charged. There is a good chance that the controller would survive the indignity of being charged with the battery but since adding an interlock to keep the line contactor from coming in when the charger is on why take the chance?
Robert" 'Freedom' has no meaning of itself. There are always restrictions, be they legal, genetic, or physical. If you don't believe me, try to chew a radio signal. " -- Kelvin Throop, III
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