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View Full Version : Breaker versus Fuse



EZwryder
29 August 2010, 1130
Does anyone use a high amp breaker in their B+ circuit? I was wondering if something like that would be preferable to a fuse as it would also allow you to disable the hot circuit when working on the bike with the battery pack installed.

EZwryder
29 August 2010, 1142
Well...yeah, I guess that's true. Of course with the breaker you'd have visual confirmation the circuit is off. The other thing I was thinking about was the reusability of the breaker. I mean, I'm not anxious to do anything to trip or blow anything. I'm just thinking that fuse was expensive and if I did something inadvertently, I'd be shelling out another $60, whereas with the breaker I could just pop the switch.

If it's a standard practice in the community to use a fuse, I'll stick with that. I just started thinking about all this because I built my little 72v battery pack yesterday and I could just sense the amount of juice stored in that thing...

electriKAT
29 August 2010, 1154
There are a few wiring diagrams posted on here. I think most people do not use a breaker in addition to the fuse. But it's personal choice. I use one for all of the reasons you say, plus the breaker energizes my DC-DC converter. With the breaker off, everything is off. With the breaker on, the DC-DC is on and then the contactor can be closed when I turn the key. But either way is fine. It's your design; do what feels right.

EZwryder
29 August 2010, 1225
Okay, that's cool. I just didn't know if there was some reason NOT to use one. I have a fuse already ordered, so I'll use that in the first rev.

Speaking of your DC converter -- did you buy that directly from Vicor or from a distributor? I was trying to figure out how to buy one off their site because they have a "Cart" function, but I couldn't figure out how to buy from them direct online.

electriKAT
29 August 2010, 1238
I used the website to find the MD rep, then I ordered it through them. You can still use the Vicor website to configure it though, so you'll have a part number. I think I told the rep what I wanted and he verified I configured it properly. There are WAY too many options. In case you're interested, here is the one I used: Vicor V72B12E250BL 72V to 12V, 250W "mini". It's maybe 2" square and a little thicker than a match book. Crazy.

Another nice thing about Vicor, their tech support is great. When I first installed my DC-DC converter, I overlooked something and it didn't work properly. I called tech support and spoke to an actual person. He figured out the problem in 5 seconds.

EZwryder
29 August 2010, 1323
Thanks for the product number. I think when I went through the process, that was what I came up with, but I wasn't sure about the mounting type, so that's very helpful.

I am going to use that inexpensive Chinese converter I bought from eBay on this first prototype because with these scooter batteries I will have plenty of space. But when I change over to lithium, I will also upgrade to this converter because space will be at a premium then. And this Vicor converter is just so danged small!

BaldBruce
29 August 2010, 1800
Keep an eye on e-bay for those Vicor modules. I found a main and a boost module for 20 bucks each.....

BaldBruce
29 August 2010, 1811
Breakers are the way to go IMO. They just cost too much for high voltage and high current ones.

BaldBruce
29 August 2010, 1833
You could check out the marine industry. Something like this? http://www.lesscoelectronics.com/ProductDetails.asp?ProductCode=CIRCUIT+BREAKER whicj I used on a boat. (but was only 24V system)

frodus
29 August 2010, 1943
Ed,
Vicors are sealed.... and pretty robust. And they'll current limit, so you can't overload them. All sorts of voltages too. You can completely short the output and they'll just limit the current. The Vicor I soldered for John was really really small, and 250W.


Dale,
As far as fuses, they're cheap. $60 is way too expensive. those ANN fuses are just fine, cost me $4 or so at the local forklift repair place.

EZwryder
29 August 2010, 1952
Dale,
As far as fuses, they're cheap. $60 is way too expensive. those ANN fuses are just fine, cost me $4 or so at the local forklift repair place.

Well that was kind of my impression too, but I didn't know any better. Now I do though, thanks!

d.

EZwryder
29 August 2010, 1959
Dale,
As far as fuses, they're cheap. $60 is way too expensive. those ANN fuses are just fine, cost me $4 or so at the local forklift repair place.

Frodus, forgot to ask - what size are you using?

frodus
29 August 2010, 2048
I used to use a 400A, Now I need to find a 600A one.

EZwryder
30 August 2010, 0534
I used to use a 400A, Now I need to find a 600A one.

Is that because you blew through the 400 when you twisted the throttle?

frodus
30 August 2010, 0816
No, its because I have a completely different setup. 400A was with SLA's and a series wound motor/synkromotive controller, and the batteries were the weak spot. We had the controller current limit at ~500A on the motor side (150A max seen on battery side). The motor/controller setup I'm using now is a 550A Curtis AC controller and AC15.

Fuses shouldn't be there to protect from overcurrent, that should be done in the controller. They're there to protect the battery pack from a catastrophic short. I'd say go 10-25% above the max current of the controller and get a fuse that is close to that. Also, fuse as CLOSE to the battery pack as possible, on the terminal if you can. Reason: If you have a short between the fuse and battery, there is nothing to protect it.

EZwryder
31 August 2010, 0702
Yes, we have the same controller, that's why I was curious how you determined the rating for your fuse.

Have you had any opportunity to use that Curtis programmer? I'm hoping I'll have need of it some time in the near future!

ardhout
24 June 2011, 0125
Fuses shouldn't be there to protect from overcurrent, that should be done in the controller. They're there to protect the battery pack from a catastrophic short.

Which fuses can be used? Slow, Fast (F) or Very Fast (FF, for semiconductor protection) ?
With a short circuit, the Amps will rise very fast (so does heat in the battery), does the battery pack suffer when using a Slow Fuse ?

frodus
24 June 2011, 0831
Yes, we have the same controller, that's why I was curious how you determined the rating for your fuse.

Have you had any opportunity to use that Curtis programmer? I'm hoping I'll have need of it some time in the near future!

I've used the programmer mostly to check settings on a few controllers that have gone through my hands.... works great.

frodus
24 June 2011, 0832
Which fuses can be used? Slow, Fast (F) or Very Fast (FF, for semiconductor protection) ?
With a short circuit, the Amps will rise very fast (so does heat in the battery), does the battery pack suffer when using a Slow Fuse ?

depends on your need.... which for an EV, slow should be fine. I'd use an ANR fuse, as pointed out earlier. Slow fuses clear just fine for what we're working with.

Allen_okc
24 June 2011, 1017
this is what im using on my bike, from Kelly... there not circuit breakers, but they are cheap...

http://kellycontroller.com/fuses-c-34.html

frodus
24 June 2011, 1030
yeah, that's the style. ANN, CNN. ANE, ANR.

Careful with the voltage though. I think they're 72V rated fuses, but a little over isn't too bad. If you're above 120V, I'd say get a fuse rated for that voltage.

Allen_okc
24 June 2011, 1035
Thank You Frodus - i wasnt aware of the voltage rate... Kelly recommended it to me for th 48 volt system, with a mention from me that i eventually would be going to a 72 volt system...