[EVDL List]

Yesterday, I had the circuit breaker trip in my EV for the first time, and I wanted to see if the explanation I've come to sounds reasonable. There's a steep, short hill on 800 South, speed limit 30 MPH. Normally, I take it in 2nd gear, but the car can't keep up to speed in 2nd, so I accelerate to about 37 MPH, then by the time I reach the top, I'm at 30 MPH. Yesterday, with my wife in the passenger seat and about 50 pounds of groceries in the trunk, I decided to take the hill in 3rd gear. Worked fine. I actually went up the hill at about 37 MPH the whole way. "Great!" I thought. When I neared the crest of the hill, I took my foot off the pedal and coasted toward the next red light. But when the light turned green and I stepped on the accelerator, nothing. Pulled over to the side and the road and opened the hood. Positive breaker had tripped.
Now, here's the explanation I want to run by you guys. I have two packs in parallel, and each has its own breaker. The two breakers are mechanically connected together, so that if one trips, they both trip. Each breaker is 200A. The two parallel strings, however, don't share the load equally. One is 100Ah LFP cells, and the other is 200Ah LCP cells. The LCP cells have high internal resistance and provide much less current. I'm wondering if when I let up on the accelerator, the LFP cells started to recover faster and started recharging the LCP cells, which were recovering more slowly. Current went over 200AH between the two strings, and the breaker popped.
Sound in the realm of possibility? If not, what could be the reason the that breaker seemed to trip when I let up on the pedal, not while I was climbing the hill?

Thanks.

Bill

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[EVDL List]

Bill that explanation sounds very reasonable. the old solution for
paralleling multiple batteries we used in RV systems was a series diode
with a parallel diode, that way the diode allowed both batteries to feed
the heavy load but the diode blocked transfer from the stronger battery to
the weaker and the resister allowed a controlled recharge from stronger to
weaker.
Regards,
*Dennis Lee Miles* (863)944-9913 (call noon to midnight Eastern time)
*xxx@xxx.xxx*
*+++++++++++++++++++++++++++++++++++++++++++++++*
*Offering a 12 day class July 9 to 21, 2012 in Central Florida. more info
on Web; WWW.ElectricVehicleTechnicalinstitute.COM<http://www.electricvehicletechnicalinstitute.com/>
*
++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++++
[quote] Bill Dennis <xxx@xxx.xxx> wrote:

> Yesterday, I had the circuit breaker trip in my EV for the first time, and
> I wanted to see if the explanation I've come to sounds reasonable. There's
> a steep, short hill on 800 South, speed limit 30 MPH. Normally, I take it
> in 2nd gear, but the car can't keep up to speed in 2nd, so I accelerate to
> about 37 MPH, then by the time I reach the top, I'm at 30 MPH. Yesterday,
> with my wife in the passenger seat and about 50 pounds of groceries in the
> trunk, I decided to take the hill in 3rd gear. Worked fine. I actually
> went up the hill at about 37 MPH the whole way. "Great!" I thought. When I
> neared the crest of the hill, I took my foot off the pedal and coasted
> toward the next red light. But when the light turned green and I stepped
> on the accelerator, nothing. Pulled over to the side and the road and
> opened the hood. Positive breaker had tripped.
> Now, here's the explanation I want to run by you guys. I have two packs
> in parallel, and each has its own breaker. The two breakers are
> mechanically connected together, so that if one trips, they both trip.
> Each breaker is 200A. The two parallel strings, however, don't share the
> load equally. One is 100Ah LFP cells, and the other is 200Ah LCP cells.
> The LCP cells have high internal resistance and provide much less current.
> I'm wondering if when I let up on the accelerator, the LFP cells started
> to recover faster and started recharging the LCP cells, which were
> recovering more slowly. Current went over 200AH between the two strings,
> and the breaker popped.
> Sound in the realm of possibility? If not, what could be the reason the
> that breaker seemed to trip when I let up on the pedal, not while I was
> climbing the hill?
>
> Thanks.
>
> Bill
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere. Thanks.
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[EVDL List]

Circuit breakers trip when the current is over the limit for a certain
time.
So, you may be able to climb the hill in 3rd gear and pulling 400A
without tripping the breaker immediately but likely it tripped towards
the crest of the hill and you only noticed when you tried to drive away.
It is unlikely that the LCP pack sucks more amps than it can deliver,
so I expect that once you stop pulling major current (for example
300A from your LFP pack and 100A from the LCP pack for a total of 400A)
then there will be an equalizatoin current in the same order of the
LCP pack current - around 100A.
So the issue is not whether you went over 200A but how long you pulled
more and how much more. The further over the breaker limit, the faster
it will trip.
My conversion also has a (dual) 200A breaker (in + and - from battery)
and I routinely pull 300-320A upon acceleration and maintain freeway
speed at just under 200A. I have not tripped the breaker until now but
I may need to go for a 300A breaker if I increase the max battery
current to 500A.

Regards,

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: xxx@xxx.xxx Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203

-----Original Message-----
From: xxx@xxx.xxx.edu [mailto:xxx@xxx.xxx.edu] On
Behalf Of Bill Dennis
Sent: Monday, June 25, 2012 6:43 AM
To: Electric Vehicle Discussion List
Subject: [EVDL] Circuit Breaker Trip Reason

Yesterday, I had the circuit breaker trip in my EV for the first time,
and I wanted to see if the explanation I've come to sounds reasonable.
There's a steep, short hill on 800 South, speed limit 30 MPH. Normally,
I take it in 2nd gear, but the car can't keep up to speed in 2nd, so I
accelerate to about 37 MPH, then by the time I reach the top, I'm at 30
MPH. Yesterday, with my wife in the passenger seat and about 50 pounds
of groceries in the trunk, I decided to take the hill in 3rd gear.
Worked fine. I actually went up the hill at about 37 MPH the whole way.
"Great!" I thought. When I neared the crest of the hill, I took my foot
off the pedal and coasted toward the next red light. But when the light
turned green and I stepped on the accelerator, nothing. Pulled over to
the side and the road and opened the hood. Positive breaker had
tripped.
Now, here's the explanation I want to run by you guys. I have two packs
in parallel, and each has its own breaker. The two breakers are
mechanically connected together, so that if one trips, they both trip.
Each breaker is 200A. The two parallel strings, however, don't share
the load equally. One is 100Ah LFP cells, and the other is 200Ah LCP
cells. The LCP cells have high internal resistance and provide much
less current. I'm wondering if when I let up on the accelerator, the
LFP cells started to recover faster and started recharging the LCP
cells, which were recovering more slowly. Current went over 200AH
between the two strings, and the breaker popped.
Sound in the realm of possibility? If not, what could be the reason the
that breaker seemed to trip when I let up on the pedal, not while I was
climbing the hill?

Thanks.

Bill

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| Please take those discussions elsewhere. Thanks.
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