overheating batteries & f/r switch

ruste415 · 09-23-2020, 07:27 PM

hi all,
got some questions here for you. 1994 ezgo marathon, electric cart. when I bought it a few years ago, found motor was toast. brushes welded onto armature, just destroyed. anyway, replaced motor with AMD ES1-4002, which was supposed to give me a bit more power. its a 36v cart, which everybody tells me I should upgrade and more about that later...but i melted a battery terminal down the first time i took this cart up a hill after changing motor. after that, i upgraded my controller to 325A Curtis and upgraded battery cables to #2AWG. Also changed solenoid. Burned up f/r switch, replaced that with hd switch. Changed to new batteries. Overheated hd switch. most recently i shuffled batteries around, (2 are newer than other 4 due to melting down terminals on batteries), ive noticed that the last battery in line, + terminal on - side of series circuit is the terminal that gets the most heat. also still gets rather hot on hd switch. i brought this to a cart shop, they told me that they would have done exactly what i did, and had no other solution than to switch to a 48v cart. which my controller and motor are apparently capable of doing, but im leery of buying new batteries without first ironing out current issues. thanks for you guys time, and sorry for the novel, but im running out of ideas on this cart.

JohnnieB · 09-24-2020, 09:37 AM

The six 6V batteries are connected in series and the same number of amps pass through all points in a series circuit, so if some battery terminals are getting hotter than the others, then those battery terminals have more resistance than the others.

The reason for the excessive resistance could be cable related issues, or over-tightening of the nuts on the battery's stud terminals.

Undersized conductors, poor construction or corrosion are the most common cable issues.

The stud type battery terminals are simply stainless steel hex bolts with the head embedded in the lead of the battery post. If too much torque is applied, the hex head rotates in the soft metal and only the six points remain in contact, so the resistance of the SS to Pb interface skyrockets. The torque spec for the nuts is 95 to 105 INCH/lb, which translates to 7.92 to 8.75 ft/lb.

------------
There are a lot of F/R switches that are advertised as HD, but are not HD. At best, even a true HD F/R switch is a weak link in the amp delivery system of a series drive. Upgrading to a reversing contactor may be needed if going to 48V doesn't solve the F/R overheating issues.

--------------
Going to 48V reduces the number of amps needed to do the same amount of work by 1/3. In other word. if your motor was drawing 150A to climb a hill with a 36V battery pack, it would only draw 100A to climb the same hill with a 48V battery pack. Since Amps squared time resistance equals heat (I² x R = W) the 1/3 reduction in amps is a major reduction in heat.

ThreeCW · 09-24-2020, 01:14 PM

Great reply JohnnieB … you covered a lot of good information.

Ruste415. Welcome to BGW.
Have a read of the attached Trojan document that discusses excessive heat. Heat at terminals is not an uncommon problem but can be prevented with proper attention to reducing the resistance at or near the terminals.

One other thing worth highlighting is in cases where you have more than one wire / cable connected at a terminal, you must have the highest amperage lug (i.e. your big cables) at the bottom of the connection stack in direct contact with the battery terminal. This will give you the lowest possible resistance at that connection.

Perhaps post a photo or two of where you are having problems. That might help with the troubleshooting of your heat problem.

If you have addressed the common causes of resistance (heat) at a terminal and have not resolved it, try replacing that battery cable with a GOOD quality new one. Problems can lurk inside a cable and replacement is sometimes the only option. As JohnnieB pointed out, over-torqueing can permanently damage your battery terminal as well and if the stud it loose ... that is a problem.

ruste415 · 09-24-2020, 05:17 PM

thanks a lot for the replies and the info. gives me some new stuff to attack. appreciate all the help

09-23-2020, 07:27 PM	#1
ruste415 Not Yet Wild Join Date: Sep 2020 Posts: 2	overheating batteries & f/r switch hi all, got some questions here for you. 1994 ezgo marathon, electric cart. when I bought it a few years ago, found motor was toast. brushes welded onto armature, just destroyed. anyway, replaced motor with AMD ES1-4002, which was supposed to give me a bit more power. its a 36v cart, which everybody tells me I should upgrade and more about that later...but i melted a battery terminal down the first time i took this cart up a hill after changing motor. after that, i upgraded my controller to 325A Curtis and upgraded battery cables to #2AWG. Also changed solenoid. Burned up f/r switch, replaced that with hd switch. Changed to new batteries. Overheated hd switch. most recently i shuffled batteries around, (2 are newer than other 4 due to melting down terminals on batteries), ive noticed that the last battery in line, + terminal on - side of series circuit is the terminal that gets the most heat. also still gets rather hot on hd switch. i brought this to a cart shop, they told me that they would have done exactly what i did, and had no other solution than to switch to a 48v cart. which my controller and motor are apparently capable of doing, but im leery of buying new batteries without first ironing out current issues. thanks for you guys time, and sorry for the novel, but im running out of ideas on this cart.
ruste415 Not Yet Wild Join Date: Sep 2020 Posts: 2

09-24-2020, 05:17 PM	#4
ruste415 Not Yet Wild Join Date: Sep 2020 Posts: 2	Re: overheating batteries & f/r switch thanks a lot for the replies and the info. gives me some new stuff to attack. appreciate all the help
ruste415 Not Yet Wild Join Date: Sep 2020 Posts: 2

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09-24-2020, 09:37 AM	#2
JohnnieB Techno-Nerd Join Date: Jun 2011 Location: West Virginia Posts: 19,654	Re: overheating batteries & f/r switch The six 6V batteries are connected in series and the same number of amps pass through all points in a series circuit, so if some battery terminals are getting hotter than the others, then those battery terminals have more resistance than the others. The reason for the excessive resistance could be cable related issues, or over-tightening of the nuts on the battery's stud terminals. Undersized conductors, poor construction or corrosion are the most common cable issues. The stud type battery terminals are simply stainless steel hex bolts with the head embedded in the lead of the battery post. If too much torque is applied, the hex head rotates in the soft metal and only the six points remain in contact, so the resistance of the SS to Pb interface skyrockets. The torque spec for the nuts is 95 to 105 INCH/lb, which translates to 7.92 to 8.75 ft/lb. ------------ There are a lot of F/R switches that are advertised as HD, but are not HD. At best, even a true HD F/R switch is a weak link in the amp delivery system of a series drive. Upgrading to a reversing contactor may be needed if going to 48V doesn't solve the F/R overheating issues. -------------- Going to 48V reduces the number of amps needed to do the same amount of work by 1/3. In other word. if your motor was drawing 150A to climb a hill with a 36V battery pack, it would only draw 100A to climb the same hill with a 48V battery pack. Since Amps squared time resistance equals heat (I² x R = W) the 1/3 reduction in amps is a major reduction in heat.