Hi There Darryl, Your recommendation to customers is 100% accurate… It is better to use low charge currents
There is really no limit to how high the initial charge current can be. A good way to determine how high the initial charge current can go is to use the Ampere hour law, which states that a battery can accept as much current as it needs capacity until it reaches a full state of charge. That is, if 100 ampere-hours have been discharged, the initial charge current can be as high as 100A. However, (as you correctly pointed out) fast charging will adversely affect the battery. Fast charging affects the components of the battery in different ways. For example, in the case of the positive electrode, high charge currents will adversely affect the electrochemical activity and crystallization of the positive active material. This will change electrical behavior of battery. In the case of the negative electrode, the effect of the high charge current is the slower diffusion of the sulfuric acid from the pores on the negative plate towards the bulk solution. This causes the concentration of sulfuric acid inside the negative active mass pores to increase, and consequently, the solubility of lead sulfate. Fast charging also tends to structurally stress the electrodes, and may also increase the battery’s temperature. The general effect is a reduced cycle life and capacity. Several tests have revealed that when a battery is cycled at a specific charge current, and periodically, the charge current is increased by twice as much current, the capacity declines. The capacity declines even more if the charge current is tripled. Once the charge current is restored, so is the capacity. It is usually recommended to use a range of 10% to 13% of the battery’s 20-hour rate. Generally speaking, there are two things that one has to keep in mind when using high currents. The first one is that the current must be lowered once the battery reaches the gassing voltage, which is 2.35 volts per cell for most designs. The second one is that the battery cannot exceed 114°F. If the battery does reach the 114°F during the charge, or if the battery is already at 114°F, then the charge current must be lowered to the 10% to 13% range or lower. I generally tell customers that if they must use high charge currents, it is essential to include a third step with a small constant current in the charge algorithm to ensure a complete charge. Thank you for your reply. Best Regards, Ronald Paredes Technical Product Manager – Renewable Energy Trojan Battery Company 12380 Clark Street Santa Fe Springs, CA 90670 Tel: (562)236-3000 Ext. 3066 Fax: (562)236-3279 rpare...@trojanbattery.com<mailto:rpare...@trojanbattery.com> www.trojanbattery.com<http://www.trojanbattery.com/> Trojan Battery Company - Clean Energy for Life™ From: Darryl Thayer [mailto:daryl_so...@yahoo.com] Sent: Thursday, July 15, 2010 6:44 AM To: RE-wrenches Cc: Ronald Paredes Subject: Re: [RE-wrenches] Trojan L16 2v vs 6v Hi Ronald Thanks for helping with these battery questions. I think I have seen improved cycle life increase when I keep the recharge rate lower. I do not recomsnd a very large generator, in fact I tend to recomend smaller generators. I also believe in SOC charge control, where if the SOC gets low the generator is started, not based on voltage. I think a person that is trying to recharge RE type batteries is making a mistake if they want to charge in 5 hrs. They should look at 10 hrs for 60% SOC starting point. That is never charge faster than C/10 and C/15 or C/20 is better. Am I on the right track or am I deciving my self? This e-mail message and any attachments that accompany it may contain information that is confidential, privileged, or protected from disclosure. It is intended solely for the use of the individual(s) to whom it was intended to be addressed. If you have received this e-mail by mistake, or you are not the intended recipient, any reading, disclosure, copying or other use of this communication is strictly prohibited. If you have received this communication in error, please immediately advise the sender at their phone number listed above, or by electronic mail, and also permanently delete the original and all copies of this e-mail and any attachments from all locations. Thank you.
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