Re: EV Beach Buggy Outing - long

[Scott Hull <ScottHull@compuserve.com>]

Lee Hart wrote:

>This sort of charger is not very practical 144v....

>The simplest fix is to add a buck/boost transformer. Get a transformer
with a
>12v 15amp secondary. Wire switches so you can select "high" = 120vac line
>voltage + 12vac secondary, "medium" = 120vac line alone, or "low" 120vac -
>12vac secondary.

After reading this I was planning on ripping the transformer out of a spare
12 volt battery charger. While I was inspecting the circuit in a 12 volt
battery charger, I had another brainstorm - What if I wire the DC output of
the 12 volt charger in series with the recitfied 120 volt line?

Lee - please comment.

I tried it and it seems to be working. The 12 volt charger that I'm trying
first is a manual charger with a LOW-HI switch to select 2 or 6 amps. the
switch seems to give some control - 4 amps on low and 5 amps on high with
the 144 volt pack. When I connect to a single 12 volt battery in the same
pack, it gives me 1.5 on low and 5 on high, so it appears that the low
setting is affected more. I have a 12 volt, 10 amp automatic charger that I
will try next to see if it can be used to control the 144 volt charge
cycle.

Other than the fact that the setup is not isolated, is there a problem with
this?

If I have a universal input DC-DC converter/charger (switchmode power
supply) with a 12 volt output on board the car, can I use it in series with
the rectified 120 vac to charge the pack?

FYI - The straight rectified 120 vac delivered 4.9 KWH over the 12 hour
period set on the timer into a 144 volt pack that was initially at about
10-15% SOC. This was into a series pack of 12-12 volt group 24 flooded
batteries (564 lbs. total). 5 hours after the charger timer shut off, pack
voltage was 152.2 and the individual battery voltages were about 12.7
volts. I guessed that it was about 70-80% full at that point. The charge
started at about 5 amps and tapered to about 1 amp near the end.

SAH