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Discussion Starter #1
Hello.


I want some input from the community on what happened to me this week. I have a 2004 Nissan Sentra converted EV and it has been working fine since the conversion for about 13 months (it had to be 13), but this week at a red light I lost the brakes almost completely :eek:. I was lucky enough to have space from the car in front, and the hand brake assisted good enough to stop in time since I was in a flat road. The reason was that the fuse of my vacuum pump burned and then I lost the assisted braking, and considering that I have 1,400 lbs. of lead-acid battery weight…


This got me thinking of what may have happened because of a tiny little cheap fuse :(. The city where I live is all flat, but if I had been in a downhill road I don’t think I would have been able to stop the car in time.


I have had for a while a sensor that disconnects the pump when there is enough vacuum, and I am not sure why I installed a fuse that was only 5 amps (inline fuse not part of the pump), but I replaced this fuse with a 15 amps and everything seems to be working fine again, but I was wondering if people living in hilly places put an emergency secondary vacuum pump just in case.


A gasoline engine can also fail and lose the brakes, but at least there is compression in the engine to try to do something and they do not weight as much as electric cars (especially conversions). Also in gas cars, if the transmission is still engaged I figure it will generate some vacuum even if the engine is dead.



I am interested in hearing if it is common to put some kind of emergency braking in conversions because at least in DC, there is nothing to slow down the car if the brakes fail. I don't have a vacuum tank. Is this something that may have helped? an alarm if the vacuum gets below some value? Other ideas?



Jose
 

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Did it happen to be cold out when the fuse blew? I have a 6 A fuse for my pump and the first cold morning it blew. I then found out I really needed a 10A fuse because the pump needs more startup current in cold weather.
 

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I don't have any redundancy on my power brakes, but I have tested them with the pump off and I know I can still stop the car OK. It takes a heavy foot, but it will stop.
Yes, remember, "power" brakes are really "vacuum ASSISTED" brakes. If vacuum is lost, like in the original poster's case, the brakes still work, you just need to stand on them as hard as needed. If you still can not stop-- further design changes would be in order. (please test in a controlled location) I bet most here would recommend adding a tank in-line after a check valve, to mitigate the issue.
 

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Discussion Starter #7
I just bought a vacuum canister and I like a lot the gauge O'zeeke recommends because it has an alarm of low vacuum. I think I am going to get one.

Thank you.
 

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I have been driving without a vac pump for 790 miles now. I have been considering options other than installing the vacuum pump. Although it is stiff I can lock up the wheels if I need to. The big difference is I have a lithium conversion and the car is actually lighter than when it had the ICE in it. The brakes are supposed to still work even if the vacuum fails. But they never expected you to be carrying so much weight. Your car is probably around 1000 lbs overweight.

Fuses wear out from thermal cycling. What is the actual draw of the pump? If you have a meter that can record peaks you might put that in the line and see what the starting current is. Then fuse it for 25% more than that. The fuse is really only there to prevent the wiring from burning up in the event of a short.

Glad you didn't have an accident and I hope you get it sorted out to your satisfaction.
 

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I have something quite different than most. The system in my van is actually hydraulically assisted. There is a small canister that stores compressed nitrogen. In the even that the pump fails, the maker says it will be good for three assisted stops. I find it's really only good for about 1 or 2 but I haven't really had to use it. Regenerative braking helps alot, plus DC braking but this only applies for AC motors.
 

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If you have a large vacuum reservoir, you will notice your brakes fading before the vacuum assist is gone entirely. I am using an 18" by 4" section of sewer pipe.

I also used a small vacuum switch that was in my MR2 which switches at a "lower" (closer to atmospheric pressure) vacuum than the actual pump switch as an idiot light sender and it has warned me a few times when the main pump didn't kick in for some reason or other.

The problem I am having right now is for some reason my vacuum pump system (the SSBC system) won't stop running. I have replaced the hoses, switching relay, and sending unit and it still runs continuously. It does cycle on and off if I hook it up to my idiot light sender instead of the OEM sender that comes with the pump. Of course, this means that the vacuum is down to almost nothing before the pump kicks in.

My only theory at this point is that the one component I have not replaced (the pump itself) is not creating as strong of vacuum as it used to and as such is not creating enough vacuum to make its own sender turn off the pump. It could be a leaking diaphragm or valves I guess. The motor is certainly fine. The system is 5 years old and has 16000+ miles (don't know how many stops that is) on it.
 

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my guess is that your brake booster has gone south for the winter and isn't coming back, ever. Not normally an issue on ICE, but we are vacuum limited.
 

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Good thought. I know that isn't the case however since the pump doesn't cycle on its own, only when I am actually using it. It will hold a vacuum while parked for several hours. I also disconnected the booster and everything else except the vacuum sender from the pump and sealed it off and ran it, and the pump still would not stop running.
 

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I have been using an autometer boost gauge to monitor my brake vacuum level.

Boost Gauge

You can get significantly better braking by upgrading your pads. I'm not talking about the best pads the discount auto parts store sells. I mean high performance street pads like the Hawk HPS or HP+. They will cost you though.

Hawk HPS
 

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Discussion Starter #14
Very interesting experiences and advices. Thank you all for sharing. I have decided to get a canister, and also check for leaks. I think I may have some as well since when the system failed I had zero vacuum left. I am also getting the electronic vacuum gauge. I will also make braking test in a controlled place to see how much I can really brake without the assisted braking system on.

Thank you again.
 

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Hello madderscience

Are you using a sensor from EV Source or like this one?

http://www.evsource.com/images/mechanical/131-PMF-4200-X30.jpg

I had a similar experience with one of these and I had to replace it because it would not stop the pump even when there was enough vacuum. The one I replaced it with fails too now and then and do not disconnect the power until I tap it a little. May this be the same problem?
 
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