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  #11  
Old 04-27-2012, 07:10 AM
TTmartin TTmartin is offline
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Question Re: Dc Dc converter best set up?

Quote,
It might be a smart idea to put a peak-holding clamp DC ammeter on the cable from the alternator to the battery to see how much current you are actually pulling from the alternator. You might find out that 40-50A is all you really need, along with a small 12V battery to smooth out the bumps along the way.

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Re: Dc Dc converter best set up?
You should really test your system to see how much you need. Mine pulls under 15 A with everything on. Unlike your motor/controller, you can test anything about the 12V system while stationary.

Ok guys, humor me I think I'm nearly there,

Unfortunately I can't put an amp clamp on to test system yet, to many things hanging loose power steering plumbed in on the hydraulics but not wired in yet.
Also planning on using 12 v water heater element designed for Solar Power not sourced yet.
But I think your saying even with the big amp draw components eg, power steering peaking at possibly 75amps the dc-dc converter at 55amps will cope most of the time with the battery taking care of the extra current when the heater or steering etc kick in, then at lower demand times dc-dc tops up battery


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  #12  
Old 04-27-2012, 07:49 AM
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Default Re: Dc Dc converter best set up?

Yes, you hopefully would not be averaging more than that. I average ~2.5, manual everything is great!
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  #13  
Old 04-27-2012, 11:14 AM
Yukon_Shane Yukon_Shane is offline
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Default Re: Dc Dc converter best set up?

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Originally Posted by TTmartin View Post
...Also planning on using 12 v water heater element designed for solar power not sourced yet...
I'm assuming that you would be hoping to use this 12v heater for cab heat in which case I might suggest doing a bit of search on the forum for previous discussion on this topic.

I don't know the specifics of the 12V product is that your looking at for heating but my sense is that it would be difficult to supply sufficient cab heat with a 12 V heating element. Most DIY EV's use atleast 1500 watt heaters for cab heat and these are typically reported to be undersized.

It's likely better to use the pack voltage for heating and avoid the need for an unnecessarily large DC/DC.

It's also worth noting that Evnetics is working on a DC/DC converter that will handle your proposed pack voltage with ease.

Tesseract is likely not mentioning his work on this out of respect for the forum rules but I think it's relevant to this discussion.
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  #14  
Old 04-27-2012, 08:31 PM
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Default Re: Dc Dc converter best set up?

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Originally Posted by Yukon_Shane View Post
It's also worth noting that Evnetics is working on a DC/DC converter that will handle your proposed pack voltage with ease.
I hope this is true. I'd be willing to buy one now for delivery in 6-12 months (I still have a ways to go on my conversion). There is a big hole in the market for a quality DC-DC converter.
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  #15  
Old 04-27-2012, 10:47 PM
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Default Re: Dc Dc converter best set up?

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Originally Posted by TTmartin View Post
Thank you,
this makes total sense now my confusion came due to a lot of the conversions out there seem to have quite small DC-DC, eg 55amp output, if your running with power steering, 12v heating etc I think a larger output is required, can anyone point me in the right direction to a good manufacturer for dc-dc converter to go from around 200v to 12+ with enough output. I think the Iota 55 is to small and seems not to have a good name for EV's although it's the most used, from what I can see.
You might want to search ebay for VICOR VI-251-09 bricks. They are available from time to time for a decent price. The 09 has an input voltage range of 150-250v and they are easy to parallel. I currently use three for about 44A output. It seems many people aren't too fond of VICOR but I haven't had any problems.
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  #16  
Old 04-28-2012, 07:00 AM
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Default Re: Dc Dc converter best set up?

Yeah, using 12V for heating is just plain crazy. If you find you need 100A+ of 12V in your EV then you are doing something wrong. Probably something like using a 12V cabin heater!

And yes, the rumors are true - I got tired of hearing complaints from Rebirth Auto about how crappy it is to use an off-the-shelf switchmode power supply (SMPS) as a dc/dc converter. My dc/dc is going to be significantly more expensive than a plain old SMPS mainly because it will be designed for the harsh environment of an on-road vehicle - a die-cast sealed aluminum box, at least a 4:1 input voltage range (max of 425V - same as a Shiva), easily paralleled, highly abuse resistant, etc... I won't know for sure how much output current I can get out of the available enclosure sizes, transformer cores, semiconductors, etc, until I build a prototype, but it will be in the range of 30-50A at a fixed voltage of 14.0V. Depending on the connector(s) - if any - used for the wiring I might also include remote sense (to compensate for voltage drops in the wiring) and remote shutdown (to physically disconnect the converter from the traction pack when the car is off).

Finding a suitable connector - especially for the high current 12V side - is often the hardest part in designing an electronic product. Most EEs will agree that all connectors suck in one way or another. I want our dc/dc to at least be splash-proof, like our controllers, so that eliminates a lot of the "low hanging fruit" in connector selection.

Finally, the Vicor modules are good products, but also not designed for the EV environment. You should add a ripple filter ahead of the DC input, a heatsink for the modules to bolt onto, and you have to solder the wiring to "staked pins" yourself. They are more in the "rolling science project" category of solutions, rather than a polished product, but using them is perfectly reasonable for technically-savvy DIYers. Conversion shops can't exactly rely on the supply of surplus modules on eBay, however, as these Vicors are not cheap when purchased brand new.
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  #17  
Old 05-01-2012, 03:23 PM
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Thumbs up Re: Dc Dc converter best set up?

I just joined your forum and I would like to add some of my expertise and experience with DC-DC converters and other components that are useful for EVs. I have installed a 240/480 V, 2 HP 3-phase induction motor on a stripped-down riding mower, and I built a DC-DC converter which takes 12 VDC from a small SLA battery and provides 320 VDC for the DC link of a standard VF motor controller. In its final form, it should be able to provide 1500 watts, or 2 HP, from two or three batteries in series (24 or 36 volts). The same design can be upgraded to higher power and voltage, or multiple units could be connected in series or parallel for the power needed.

I was able to build this using surplus and junk power components, and a few simple items like a Microchip PIC. So it really cost almost nothing except my time designing and building it. If it works well enough, I may enhance the design and put the circuitry on PC boards to simplify assembly. I think this can be built for something like $50/kW, even using new components. If you are interested, I'd be happy to assist you in building a similar unit. Here is a video showing my first ride using these components:

http://youtu.be/y0qWY4bVnEA

See my introductory post for other details.
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  #18  
Old 05-02-2012, 01:44 PM
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Default Re: Dc Dc converter best set up?

Does anybody have any good suggestions for a compact 12 volt gel battery mentioned above? Not much room to work with, as I didn't expect to be using a 12v cell. Brand, model?

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  #19  
Old 05-02-2012, 03:01 PM
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Default Re: Dc Dc converter best set up?

This is the size I use. I like to use a 12 volt AGM battery with a capacity of around 20 amp hours. This is the size used in the old Zappy scooters.
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  #20  
Old 05-02-2012, 03:30 PM
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Default Re: Dc Dc converter best set up?

Quote:
Originally Posted by PStechPaul View Post
I just joined your forum and I would like to add some of my expertise and experience with DC-DC converters and other components that are useful for EVs. I have installed a 240/480 V, 2 HP 3-phase induction motor on a stripped-down riding mower, and I built a DC-DC converter which takes 12 VDC from a small SLA battery and provides 320 VDC for the DC link of a standard VF motor controller. In its final form, it should be able to provide 1500 watts, or 2 HP, from two or three batteries in series (24 or 36 volts). The same design can be upgraded to higher power and voltage, or multiple units could be connected in series or parallel for the power needed.

I was able to build this using surplus and junk power components, and a few simple items like a Microchip PIC. So it really cost almost nothing except my time designing and building it. If it works well enough, I may enhance the design and put the circuitry on PC boards to simplify assembly. I think this can be built for something like $50/kW, even using new components. If you are interested, I'd be happy to assist you in building a similar unit. Here is a video showing my first ride using these components:

http://youtu.be/y0qWY4bVnEA

See my introductory post for other details.
great work I need some water pumps etc.
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