Voltmeter question...Oh, and a cable size ?

DaveTM

So, I've been cruising and lurking and reading mostly the post about battery issues and battery cable sizes and charging questions. I seem to absorb this engineering "stuff" in very small quantities. Now, in all fairness my chosen profession.....when I worked....was being a CPA. So, I can talk Alternative Minimum Tax, Estates and Trust taxation, LLC's, LLP's, taxation of disregarded entity's and "stuff" like that all day long. But....who really want's to do that?

So....just a couple of question:

#1--Voltmeters: I picked up a Voltmeter a few years ago and it only cost about $15. However, I got curious about my current 8-pack of T-105's, so I measured each battery and my meter showed 6.3-V on each one, and it showed the "pack" full charge, after a two day sit in my heated garage, at 65 degrees, of 51.4-V. This seemed "normal" or good to me. But my Voltmeter question is...should I look to buy a new one that gives me readings with at least a two decimal's? So, instead of a reading of 6.x, I would get a reading of 6.xx. I would think I could find an inexpensive one (say $25?) that would do this for me.

#2--While I'm asking questions, let me toss out this one. My 48-V system has 4-ga. welding cable with crimped on copper lugs. 4-ga is .20" in diameter. Now, I know there is welding cable that is 2-ga that is .25 in diameter and welding cable that is 2/0 which is .36" in diameter. So, I am considering going to the 2-ga. welding cable and going with soldered on copper lug for all battery wires and contactor and motor wires. This would be the 2-GA. and NOT the 2/0 welding cable. The 2-ga. is the "Standard"? Am I correct when I say that??

Thanks.

Dave

BGW

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crash test dummy

i would go with a better Digital Multimeter

what i use

http://www.homedepot.com/p/Commercia...232B/202571334

the 2-GA. is a great choice

radioman

MPJA (Marlin P Jones) item number 19113TE $6.95 will work.
http://www.mpja.com/Digital-Multimet...fo/19113%20TE/

bigstik40

Not sure what meter you have, but you could try changing to a lower range (if it has one) when you measure individual batteries. example: use the 200 volt range (if you have it) for measuring the whole pack and 20 volt range (if you have it) for measuring individual batteries. The 20 volt range would/should give you readings to 2 decimal places up to 20 volts. A newer meter would be in order if your present one is limited in the number of available ranges it has. Hope this helps - Ray

JohnnieB

1. It is difficult to tell if a DVM will read ~6V as 6, 6.x, 6.xx or 6.xxx just by looking at them.

IIRC, the Innova 3340 I have reads 6.xxx and I'm pretty sure the 3320 does also. If not, it still reads 6.xx.


2. The standard for standard carts is 4Ga, but you don't have a standard cart.

For your 650A controller, Alltrax recommends a minimum of 2Ga.
Since you are running 48V, which uses 33% less current than a 36V system, 2Ga should suffice.

1 Ga, 1/0 Ga or 2/0 Ga would be more efficient, but a lot more cumbersome to work with and you probably wouldn't notice any difference in torque or speed.

The voltage drop at 650A of current flow with 2Ga cables is about 2V and about 1V with 2/0Ga cables, so torque loss is about 4% and 2% respectively, which is insignificant when you consider how far the pack voltage drop when 650A is being drawn from it.

Top speed will be essentially the same since your cart probably doesn't draw more than 75A at top speed and the voltage drop at 75A is next to nothing in 2Ga and thicker cables.

DaveTM

I quoted JohnnieB because I use my cart 95% of the time for hunting. As such, it's really very rare that I obtain "top speed" when using it. Most of the time I'm going at half-speed or even less. BTW, top speed is about 7 to maybe 9 MPH on a flat.

Thanks for all of your suggestions. I will try the 200-V range when I measure the pack as my meter does have that setting.

My existing 4-ga cables do get warm (not hot) on a long up hill run, but I expect with 2-ga soldered warm may not be in my vocabulary any more. I'll find out.

Thanks again. Dave

sunking

FWIW Assuming you are using quality compression terminals like T&B or Burndy with the proper compression tool will not only be stronger mechanically than a soldered connection, but lower resistance electrically.

JohnnieB

According to Trojan Battery a crimped and soldered terminal is the best.

Please note the the temperature scales are different for the two IR photos in the attached JPG.
My guesstimate is that the crimped connector is about 237°F while the crimped&soldered connector is about 169°F, or about 68°F cooler.

The attached PDF is the Trojan Battery White Paper in its entirety.

Personally, I prefer silver soldered cable lugs, but I attended NASA's soldering school back in the early 70's, so I'm old school.

Attached Images

Trojan cable lugs.jpg (250.1 KB, 0 views)

Attached Files

WP_BatteryCableGuide_0512-1.pdf (293.1 KB, 0 views)

crash test dummy

that explains a lot

DaveTM

My thinking was to use a Fusion Standard copper lug. These are "pre-loaded" with flux and solder for the size wire the user is going to use. You just heat the lug to the melting point of the solder, insert your pre-stripped wire into the lug and allow to cool. Done.

I've previously used the "smash crimp" tool which has worked fine. Since soldered connections seem to be touted as much better I can't see where this would be bad.

FWIW

Dave