Thought I had a DPI charger failure, but didn't

[JohnnieB]

There wasn't a core charge when I bought the seven Exide batteries I'm using for a 42V pack, so I kept the original T-105 batteries in the 36V pack and I've been keeping them alive for nearly four years with the 36V DPI Accusense charger I was using. (I use them for various experiments. )

Anyway, yesterday afternoon was sunny and 70°, so I checked the fluid levels in my cart batteries, ran it around the bumpy property to agitate the electrolyte (it stratifies when sitting still for a length of time) and took quick trip into town.

Afterwards, I went over to the T-105's to check their fluid levels and noticed the DPI was flashing all of its LEDs. That happens occasionally if there is a power failure, so I unplugged it for the AC outlet, waited a bit and plugged it back in. It didn't start normally (usually goes to 5A on meter during the pre-qualification stage , but only went to about 2A this time), then went into the bulk charge stage for only a few seconds, but amps didn't rise to 18A as usual and then started flashing the LEDs again.

That charger has been plugged into AC power nearly continuously for about 5 years and connected to a 36V battery pack almost as long, whenever I wasn't using the cart, or playing the the batteries after they were removed from the cart.

The DPI charger only has two parts, transformer and PC board and I could hear the transformer humming, so I figured the PC board had bit the dust was planning on digging out my old PW-II after I checked the fluid levels.

I noticed there was some corrosion buildup on some of the battery terminal and when I started taking off the cables (OEM cables the came off the cart when I installed 2Ga silver soldered cables, my first upgrade), I noticed the nuts on the studs were loose enough that I could wiggle several of the cable ends.

After cleaning the battery posts and cable lugs and reconnecting everything with the proper torque, I gave the DPI another try and it went through its start up process normally. Today it was on float charge as it should be, so the problem was the loose cables and corrosion.

I have no idea how the nuts got loose. They were torqued to about 9 ft/lb last November, the last time I checked the fluid levels in the T-105s.

I can understand how the battery terminal nuts can loosen when the batteries are in a cart (Vibration, frame flexing, etc.), but these batteries are sitting on a concrete floor and never get moved.

Bottom Line: If your DPI charge misbehaves, check the battery cables.

[scottyb]

I wonder if hot / cold contraction and expansion is responsible?

[gornoman]

I have the solution. Later....

[JohnnieB]

Originally Posted by scottyb

I wonder if hot / cold contraction and expansion is responsible?

Possibly, but it hasn't happened before and they have been sitting in the same spot for several winters.

Also, not all of them were loose.

Of course, I might not have noticed them being slightly loose since my fingertips aren't as well calibrated CCW as they are CW.

My normal routine is to loosen the nuts about half a turn or so, rotate the cable lug on the terminal a bit and then re-torque the nuts to about 9 ft/lb.

I think I have figured out why the DPI shut down. Bulk charge is a constant current stage, so the dpi kept increasing the voltage to get 18A to flow and ran out of voltage, so it knew something was wrong and shut down.

[scottyb]

Pretty smart charger

[gornoman]

Originally Posted by gornoman

I have the solution. Later....

Sorry, I was in the car.

When you tighten the terminal nut you actually compress the lead post slightly, causing a slight "mushrooming" effect to the lead tower. This compression will relax down the tower effectively "loosening" the compression applied resulting in a lug that is now looser than it was when originally tightened. Using the cart and creating vibrations only speeds the process up, but if left alone on your garage floor (or wherever) the relaxation still occurs. Eventually.

That's my story, and I'm sticking to it.

[JohnnieB]

Sounds as reasonable as anything I've thought of.
I'll have to look into the fluid dynamic of lead.

At least I can get my head around why the charger did what it did.