This may be kind of a dumb question, but what rating of contactor do I need? It’s a 48v system, with a 700 amp controller. I’ve seen alot of people with 400 amp controllers, and 200 amp contactors… Should the amp ratings match? I honestly feel dumb that I have to ask!
700A is the motor side, and you’ll NEVER see that many amps on the battery side.
I guess it all depends on what the manufacturer recomends as the value of the main fuse. If they say 200A, then a 200A 48V contactor will work. If they say to protect with a 400A, then a 400A contactor is required.
Also, make sure your batteries can even supply that much without failure. Some have a peak rating of over 300A, some do not.
Thanks for that Frodus… You actually brought up my next question! I was going to use Optima D51’s x4 (48volts) …On the Optima website, they only have amperage ratings for cranking amps. My project is to use two jet starter motors (the tag reads 30vdc, 1000amp max) and two 48v 700amp Logisystems controllers. Do you think 4 Optimas could handle it? The science of it can be a little difficult to grasp at times!
From what I understand, the Optima’s are good for starting (they have good short burst), however there performance is not so good under a continuous load.
I think you want to use something else, but at the very worse case you have to add a few extra batteries to handle the amp draw.
I’d look at the largest Ah battery you can fit in the vehicle. Flooded batteries are great for High amperage systems. Just consider this, you’ve got 2 700A max controllers in parallel… thats going to take a lot of current under heavy acceleration.
Optima are good for some, but its relative to the installation. Don’t discount them, but there are other better solutions.
I think 48V is going to suck a lot of amps at low RPM, so I’d look for 100+Ah batteries. Big question is, what is this going into?
What range do you need? Also, are those starter motors sepex or series? I thought the logisystems were series controllers and that starter motors were sepex.
Thanks for the info on optimas… At this point, I’d better tell you what they’re going into! I built an aluminum motorcycle frame from scratch that weights 10 lbs. So being that it’s a motorcycle, I think large flooded batts are out. I’m not going for range at all, just pure short accelleration. Basically a drag racer with minimal street use. So, Let’s just say the motors were drawing 700 amps each on take off… The 4 Optimas have a Cranking Amp rating of 575 each (2300 amps??) …Maybe I don’t understand the “cranking amp” thing correctly, but doesn’t that mean that’s how many amps they can deliver for short bursts? By the way, they are SERIES motors… There’s alot of aircraft starters out there that were also used as generators, and those are SEPEX. On some jets, the generator was a seperate unit. Thanks for your help, and being patient with me… I’m new at this electric madness!!
I have thought about a similar project, I sand drag race and thought electric drive in a small buggy would work pretty good. Seems like a car battery would work better than a deep cycle since you would need high amps for a short duration, in my case 4-6 seconds. Could you run 8 motorcycle batteries and use 48Volt to each motor to launch and 96 volt on the top end to get more speed?
Here is a pic of a buggy I have with a motorcycle motor in it
Nice Buggy Turbotom… It’s begging to go electric though! Good idea about the starting batteries, but I think their lifespan in that kind of use wouldn’t be worth it. The reason that I’m thinking about the Optima Yellow Tops, is because they’re designed for both starting and deep cycle… I guess people use these all the time for ICE starting batts. So in theory, I should get enough amps out of them… But like I said, I’m pretty new to this, and things aren’t always what they seem! I like your idea of a volt switcher… Like an electric transmission! But I’m sure most people would say that 96 volts from start to finish would be better… I just like the concept of having a “Turbo”! I thought about having a large pack of capacitors connected straight to the motors, and having a push button to engage the TURBO BOOSTERS!!! It would be like nitrous for an electric vehicle! Of course, my imagination is better than my technical skill, so I don’t know how feasable that is!
caps would have to be connected across the 48V pack… then to the controller… putting them on the motor side is going to mess with the impedance.
I’d say go for the yellow tops, they’re great batteries. Lots of amps, they’ll be great for a drag bike.
[QUOTE=frodus;5295]caps would have to be connected across the 48V pack… then to the controller… putting them on the motor side is going to mess with the impedance.
I’d say go for the yellow tops, they’re great batteries. Lots of amps, they’ll be great for a drag bike.[/QUOTE]
For turbo mode I would consider a contactor to bypass the controller completely. Putting the caps on the battery pack will “stiffen” the pack, but I don’t think that is the effect he is looking for. A bank of 100F caps charged to double the pack voltage and connected to a double pole contactor that disconnects the controller and connects the cap bank directly to the motor would be like a “turbo” for a few seconds. It would not be catastrophic if the contactor fused, because the cap bank would discharge to the applied voltage and have little effect after that.
[QUOTE=Engineer_Bill;5346]For turbo mode I would consider a contactor to bypass the controller completely. Putting the caps on the battery pack will “stiffen” the pack, but I don’t think that is the effect he is looking for. A bank of 100F caps charged to double the pack voltage and connected to a double pole contactor that disconnects the controller and connects the cap bank directly to the motor would be like a “turbo” for a few seconds. It would not be catastrophic if the contactor fused, because the cap bank would discharge to the applied voltage and have little effect after that.[/QUOTE]
I agree, a contactor to bypass the controller and put the motor to full bat voltage is how lots of EV’rs that race do it. I was just telling him how to do caps if he wanted to try it.
It would only last a few seconds though.