For quite a while, I've maintained a 36v battery bank made up mostly of the surplus hoverboard batteries that I run in golf carts. I have a golf cart charger that can supply ~9 amps that I have on a timer so it only charges when there should be good sun.
36v lead batteries can tolerate about 50 volts while typical 36v lithium batteries can tolerate no more than about 42v. Two chemistries can be used in batteries. Lithium Iron Phosphate, known as "LFP" and Lithum Cobalt which might be known as "Lithium Ion". LFP cells, with nominal voltage of about 3.2v, can tolerate about 3.5v. While LC can tolerate about 4.2v. Four LFP cells in series can make a 12v lead replacement battery. Twelve LFP cells can make a 36v battery while only ten LC are used. For both LFP and LC, a charge voltage limit of 42v works nicely without killing the cells. In both cases, it is best to use a battery management system to insure individual cells do not exceed their upper limits even when the total voltage remains below the 42v limit.
My 9 amp charger has been modified so as to not exceed 42v and I use it to charge both LC and LFP 36v batteries.
This post was stimulated by my observations this morning. I took my spray golf cart out this morning to spray mesquite. I nearly exhausted the battery as evidenced by the cart slowing down and stalling under load. That condition is best detected by a volt meter but I have not configured an easy to use and reliable volt meter for that range. Recently, I have been using a clamp on DC amp meter to detect charge current. That is, to insure that charging is taking place.
So, this morning after I hooked up the mostly depleted golf cart, I noticed that a fully charged cart was discharging at about 19 amps while the depleted cart was charging at about 38 amps. I should have expected that but I was surprised at the high current. Most of the wiring connecting various batteries in the bank is only 14 gauge which should not handle current higher than about 20 amps.
I think you are saying that the single charger can be hooked to both carts at the same time, so in this case, the fully charged cart was actually charging the cart with the depleted battery. No burnt wires! I guess you normally charge one cart at a time, and not two at the same time.
ReplyDeleteI fully realized what I was doing. Using my bank to hasten charging a cart. Even charging a cart when the charger in inactive. The bank consisting of (right now) two carts with around 50 hoverboard batteries each, two strings of 3 12v LFP batteries, and several spare cart modules of about 8 hoverboard batteries each. My surprise was large current coming out of a cart and even even larger current going into the depleted cart. All is well. That bank of batteries also serve as PowerWall supplement.
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