On 09/16/2014 09:24 PM, Mike Nickerson via EV wrote:
I have a Mini BMS system also. I suspect the contractor might be for charging
circuitry. I have the same issues with an SSR in my system.
The Mini BMS is set up to terminate charging if necessary when a cell is over
voltage and the ignition system is off. It does this by turning off the SSR or
contactor on the AC line to the charger when it detects a cell alert with the
ignition off.
When you turn on the ignition system, it re-arms the contactor back to on, to
prepare for the next charge cycle. The problem is that the contactor stays on
all the time the vehicle is parked. On my car, it takes about 2 weeks to drain
the auxiliary battery.
I solve this by pulling the fuse to the EV control circuits which includes
power to the SSR. I've wondered if there is a better way too.
My Hyundai has been using an EVPower BMS controller all it's life.
EVPower cell modules have been replaced witn miniBMS modules. The
EVPower controller is a complete "ready to use" unit while the miniBMS
"head board" is just a starting point. The EVPower controller contains
a pack to 12v DC-DC which supplies a 20 amp SCR to switch charger input
current. To reduce demand on your starting battery, you might consider
a similar set up. The "universal voltage" wall warts are VERY
versatile. They operate on something like 85-250 volts, both AC and
DC. You can control your SCR off of the pack with the wall wart
between. The wall wart vampire load is much less significant to your
traction pack than to your starting battery.
I found some ~13.5v wall warts that I use to trickle charge starting
batteries from traction packs. As a backup to my "regular" DC-DCs.
Perhaps also of interest:
About three years ago I was dealing with how to control AC current to my
10kw charger (EMW). The 20amp SCR mentioned above wouldn't handle that
current. I tried a 40 amp SCR but it was getting too hot. AND SCRs
apparently fail "on". Certainly a potential disaster. I first had
Steve add in a heavy duty 240vac relay with a 120vac coil. That worked
well as long as I charged only at 240vac and not through a J1772. This
was discussed at length here at that time. I messed around a lot with
Lee Hart's idea of using a light bulb to get about the right voltage to
the coil but I never found the right light bulb. I finally used the SCR
(in the EVPower BMS controller) to switch AC current, either 120 or 240,
to some 12v wall warts. The wall warts now supply heavy duty relays
with 12vdc coils. That setup has worked well for about three years
switching about 12kw of charging.
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