Re: Opinions [Isolated Charger]

["Mitchell Oates" <mitchoates@prodigy.net>]

On 30 Mar 2002, at 17:06, Jon "Sheer" Pullen wrote:

> 
> > 3. GFIs are essential to safety, too, but how many people on this list
> have
> > grown exasperated at the K&W BC-20 charger's tripping GFI and bypassed it?

     Yes, amd a lot of people with K&W's with GFI's found a way to 
solve the nuisance trips without bypassing the GFI - add a second 
ignition contactor in the negative leg from the battery pack. The 
pack is completely isolated from the motor and controller, 
eliminating the nuisance trips from the combination of motor carbon 
dust and high humidity. Of course, if your batteries aren't insulated 
from the battery box/mounting frame, you'll still get nuisance trips 
from dirty batteries, or a good shock if you touch the tops of the 
batteries with an unisolated charger.
     
> 
> This isn't a money issue for me. This is a efficiency issue. However, many
> have made the _quite_ valid point that with flooded batteries, it's
> basically impossible to get good isolation. I accept that flooded cars
> should always [unless they have completely plastic, sealed battery boxes]
> have a GFI AND a isolated charger.
> 
     Basically impossible? How about basically B.S.?  You gave the 
solution yourself - put the batteries inside some type of 
containment such that they're electrically isolated from the vehicle. 
That's what I've done on my truck.
     Design the vehicle with the philosophy that it CAN AND WILL 
bite you if given half a chance, and make the basic design as 
electrically safe as possible. THEN add in grounding, GFI, and 
isolation. The last 3 shouldn't be used as an excuse or band-aid for 
cutting corners on the vehicle itself.
      When I redid the truck over 2 years ago, I put it together with 
the attitude that there might be times that I would be forced to use 
an unisolated charger without the benefit of grounding or GFI.
     The enclosed battery boxes have enough coats of primer, paint, 
and plastisol to choke a mule. All the joints are sealed with marine 
grade RTV. A layer of 3/4" hard foam insulation on the bottom and 
sides, also sealed with RTV. You could use the bloody things for a 
bathtub.
     For less than $100 worth of tubing and acid-resistant plastic 
fittings, I installed a vent system such that all the batteries were 
vented outisde the battery boxes and vehicle, keeping the batteries 
all that much cleaner. I did away with this when I moved to the new 
style USB caps which had much better gaskets and found that the 
flame arrestor discs did an excellent job of keeping acid spray 
inside. After 2 years, about the only thing I have to clean off the 
batteries is dust.
     I have two ignition contactors, one each in the positive and 
negative legs from the pack. When charging, the pack is isolated 
from the motor and controller. Even sealed plastic boxes won't 
keep you from getting a shock if the motor has enough carbon dust 
to create a ground to the frame and you're using an unisolated 
charger. Ask Madman, he got bit by my truck once. I had the 
batteries inside sealed plastic boxes with plenty of insulation. But I 
didn't have the second ignition contactor, such that the motor and 
controller were still connected to the batteries via the negative leg, 
and using an unisolated charger. He got a nice tingle when he 
touched my truck and a chain link fence at the same time. Within 
a week, I had the second contactor installed, and the problem went 
away.
     ALL the exposed high voltage connections have a rubber boot 
and/or a triple coating of liquid electrician's tape (plastisol) on 
them. The two small bussbars I use for all the auxiliary 
connections are marine grade, all the connections similarly coated, 
and have safety covers installed.
     I have clear plastic covers glued over the openings on the 
contactors. This is more for keeping junk out of the contacts, but 
also keeps fingers from inadvertently going where they shouldn't.
     I have TWO separate ground connections that I can use. One is 
a separate ground wire run with the cables from the 50 amp variac. 
Anderson also makes single wire connectors, such that you can 
run a third ground wire and plug it in without any hassle. The 
second is on the 120V plug-in on the front fender that I use for the 
batttery heaters and occasionally the Todd DC/DC when the truck 
has been sitting for a few days.
     Am I saying that isolated chargers are not worth the trouble? 
No. Am I saying that if you design the vehicle correctly that 
grounding, GFI, and/or isolation aren't necessary? No, I'd say 
you're a damn fool if you DIDN'T use them even with a carefully 
desgined vehicle.
     My gripe is that people are making it sound as if using flooded 
batteries with an unisolated charger, even with grounding and GFI, 
is a mortal sin, and that using an isolated charger is the cure-all for 
everything, making up for all the faults that may be present in the 
vehicle itself.

                                                Mitch Oates