# DC-DC Alternative



## Jan (Oct 5, 2009)

#1 No, transformers only work with AC.
#2 See #1


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## EVfun (Mar 14, 2010)

It doesn't work. The small 120 vac trickle chargers start with a transformer to step line voltage down to 12 volts. Transformers do not work on DC. Also, the car electrical system isn't really a 12 volt system, more like a 14 volt system. Lights would are a bit dim on 12 volts and fans and wipers run noticeably slower. This is why it is best to use a DC to DC converter (or an AC to DC converter that will work with a DC input) that is rated to supply the current you need for the "12" volt system.


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## Go-carter (Dec 18, 2011)

Here in Norway, lots of people are running ctek chargers on 114V DC packs, to charge their 12V aux battery. The Ctek are 230V AC chargers, but seem to work on DC. I'm going to use the ctek charger as a DC-DC when I convert my locost racecar to electricity...  Cheap and easy.


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## bruceme (Dec 10, 2008)

Yup, fair enough. I tried to find similar vregs, guess it just takes a proper buck circuit.

-Bruce


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## Sunking (Aug 10, 2009)

Not only that but linear or series type chargers are very inefficient. You really want a true DC-to-DC buck/boost switch mode converter.


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## Coulomb (Apr 22, 2009)

bruceme said:


> I currently have an IOTA 30A DC-DC, which is very nice, but is it necessary?


If you have a large enough auxiliary battery, you can charge it in the garage when you charge the rest of the pack. Personally, I don't like that idea.



> What about running a small ... trickle charger?


I don't think there is any point in trickle charging the auxiliary battery. It has pretty heavy loads (e.g. 8A from the blower on high, 10 A from headlights, various other loads that add up, and you might have large ones like electric power steering). Trickle charging isn't going to keep up with that, so either charge properly at 30+ amps, or not at all and charge only from the garage.


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## Go-carter (Dec 18, 2011)

Coulomb said:


> If you have a large enough auxiliary battery, you can charge it in the garage when you charge the rest of the pack. Personally, I don't like that idea.
> 
> 
> I don't think there is any point in trickle charging the auxiliary battery. It has pretty heavy loads (e.g. 8A from the blower on high, 10 A from headlights, various other loads that add up, and you might have large ones like electric power steering). Trickle charging isn't going to keep up with that, so either charge properly at 30+ amps, or not at all and charge only from the garage.


The beefiest Ctek handles 25 amps. If you have a normal 50Ah aux battery, I can't see any problems using that as a DC-DC, and as soon as you shut your car off it will top off your battery and keep it there. Here in Norway it costs $380. $280 on ebay. Though I'm not 100% sure this works on DC, have to be tried out.

http://www.ebay.com/itm/CTEK-Multi-...19?pt=UK_Motorcycle_Parts&hash=item5192630d73


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## Tesseract (Sep 27, 2008)

You have 3 options here in decreasing order of "goodness":

1. an _isolated_ dc/dc converter - the most popular of which is to use a "universal input" AC power supply (ie - like the Iota), even though it's kind of kludgy.

2. the original alternator - if your motor has a tailshaft you can use it to drive the OEM alternator (and/or a/c compressor and/or power steering pump). 

3. a big 12V battery - take your chances and go naked, recharging the battery when you are at home. This is so tedious and dumb it defies logic that anyone would choose it just to save a couple hundred bucks, but, well... when it comes to spending inordinate amounts of time on fruitless pursuits, I suppose I have little room to talk


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## bruceme (Dec 10, 2008)

Go-carter said:


> The beefiest Ctek handles 25 amps. If you have a normal 50Ah aux battery, I can't see any problems using that as a DC-DC, and as soon as you shut your car off it will top off your battery and keep it there. Here in Norway it costs $380. $280 on ebay. Though I'm not 100% sure this works on DC, have to be tried out.
> 
> http://www.ebay.com/itm/CTEK-Multi-...19?pt=UK_Motorcycle_Parts&hash=item5192630d73


The Iota "DC-DC" I use is actually an off the self 108-130VAC/DC to 13.5v at 30A battery charger. I know the rating says 130v, but my high voltage system runs 140-165v and it works fine. Probably the best solution period and it costs $140 delivered. Google Shopping Search. I've been using it for daily commuting for about a year and I've never touched my 12v system (just works). So I have nothing to complain about. 

-Bruce


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## ElectriCar (Jun 15, 2008)

Sunking said:


> Not only that but linear or series type chargers are very inefficient. You really want a true DC-to-DC buck/boost switch mode converter.


That sounds like something to look into. When I took electronics they weren't even mentioned, likely not invented or still in infancy. Anyway, have any suggestions? I have an Iota 55 and it sags horribly even on 165V supply. It can't possibly have a voltage regulator on the output seeing the way it operates.

I know how inefficient transformers can be at conversion and imagine my current device is not very efficient. I'm not sure whether it has a transformer or is what you describe.


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## EVfun (Mar 14, 2010)

Since the Iota is designed as a motor home battery charger its output is designed to go from a safe float voltage of about 13.7 down (must be to about 12 volts) as the load is increased toward max. This allows the load to smoothly transfer to the battery without an obvious sudden drop. The maximum output of an Iota DLS is only available when the input voltage is at least 135 volts.


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## bruceme (Dec 10, 2008)

ElectriCar said:


> That sounds like something to look into. When I took electronics they weren't even mentioned, likely not invented or still in infancy.


Hardly, they're called "switch-mode power supplies" (SMPS) and they've been around since the 20's, but transistors in the 70's made it "cheap". 

Wiki Link


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## cruisin (Jun 3, 2009)

bruceme said:


> Hardly, they're called "switch-mode power supplies" (SMPS) and they've been around since the 20's, but transistors in the 70's made it "cheap".
> 
> Wiki Link


 
Using tke IOTA as a DC converter is a bad decision based on price. Read the forums and you will see most DC converters will fail when you need them the most. Since 2005 I have used a small 16v Li-ion battery for system voltage and a couple of Vicor half brick SS DC converters full time to keep it fully charged. Low power consumption and extremely dependable.


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## ElectriCar (Jun 15, 2008)

I never heard of them until the 90's but my training was US Navy electronics which was geared toward my rating or "trade", as such I didn't have all the classes they taught.


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## spdas (Nov 28, 2009)

cruisin said:


> Using tke IOTA as a DC converter is a bad decision based on price. Read the forums and you will see most DC converters will fail when you need them the most. Since 2005 I have used a small 16v Li-ion battery for system voltage and a couple of Vicor half brick SS DC converters full time to keep it fully charged. Low power consumption and extremely dependable.


aloha, can you show me a sample of Vicor half brick SS DC converters, Maybe a link to one on Ebay? thanks
Francis


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## cruisin (Jun 3, 2009)

spdas said:


> aloha, can you show me a sample of Vicor half brick SS DC converters, Maybe a link to one on Ebay? thanks
> Francis


Just a example of what is available.


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## swoozle (Nov 13, 2011)

cruisin said:


> Just a example of what is available.



Do they come in versions that will accept 144V? Or is there some way to easily use this in a 144V build?


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## Coulomb (Apr 22, 2009)

swoozle said:


> Do they come in versions that will accept 144V?


Yes, they come in many voltage ranges for the input, and many voltage ranges and combinations for the outputs. (Often there is a fairly small range of output voltage, e.g. 13.2 to 16.7 V).



> Or is there some way to easily use this in a 144V build?


No. You have to find the one(s) with the right input and output ranges.
Edit: however, you can use *two* of them (one on each half pack), as noted by Cruisin below.


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## Ivansgarage (Sep 3, 2011)

Here is a link for dc-dc converters........This site has all the data sheets and design guides... pdf files.....

http://www.vicorpower.com/cms/home/products/brick/mini-maxi-micro-converters










1999 Sonoma Electric Vehicle
http://ivanbennett.com/index.html


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## cruisin (Jun 3, 2009)

swoozle said:


> Do they come in versions that will accept 144V? Or is there some way to easily use this in a 144V build?


They do come in various versions, however, there are a lot of things to take into account in selecting.

1) Input voltage should be as low as possible
2) Output needs to be 14v to 15v
3) Output amps need to be sufficient

I have been using these in conversions since 2005 and never had a failure.
Use the 48-75v as shown in picture on each half of pack. This avoids the HV wiring using the whole pack voltage. It will NOT unbalance your pack.
Decide how much amperage you need to determine how many to install. A small 15v Li-ion battery works real good for your system with the DC converters on full time to keep battery charged. Current usage is very small and will not run down your pack unlike power hungry DC converters. I modify the converters for a output of about 15v to keep the battery charged. Most electrics on your car will tolerate the 15v, in fact your lights will love it even the LED's. Using a Mini BMS and SOC meter, you will need a constant 12v+ for its monitoring of your pack. Without a full time DC converter, your battery could run down and poof!!!


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## spdas (Nov 28, 2009)

I don't understand the reason for using the 48-75v on each half of pack rather than a 144v or so version. Please explain.

thanks
Francis


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## cruisin (Jun 3, 2009)

spdas said:


> I don't understand the reason for using the 48-75v on each half of pack rather than a 144v or so version. Please explain.
> 
> thanks
> Francis


Sure, less heat generated reducing 75v to 15v than 150v to 15v. Also, you do not want wiring running around the car with the full pack voltage for all kinds of reasons. 75v versions are 1/2 the size of the 150v versions (1/2 brick instead of full brick). These devices are so dependable you will never have to replace them. There probably isnt a conversion out there using the original DC converter unless it is one of the higher ($500+) end type like Zivan etc. Lastly, look at the size compared to the junk IOTA. No competition here. Many will defend the cheap converters because it is all about money, period.


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## ElectriCar (Jun 15, 2008)

cruisin said:


> Sure, less heat generated reducing 75v to 15v than 150v to 15v. Also, you do not want wiring running around the car with the full pack voltage for all kinds of reasons. 75v versions are 1/2 the size of the 150v versions (1/2 brick instead of full brick). These devices are so dependable you will never have to replace them. There probably isnt a conversion out there using the original DC converter unless it is one of the higher ($500+) end type like Zivan etc. Lastly, look at the size compared to the junk IOTA. No competition here. Many will defend the cheap converters because it is all about money, period.


My 2008 Iota DLS55 has 12K miles on it. Yea it works but doesn't do a great job. I converted my marker lights to LED first thing. Only head and tail lights are incandescent and courtesy lights inside. I'm probably going to convert to a Vicor whenever I figure out which one to use. I have a 50 cell pack that maxes at about 173V.


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## Coulomb (Apr 22, 2009)

cruisin said:


> Sure, less heat generated reducing 75v to 15v than 150v to 15v.


Well, it's more efficient to buck smaller ratios of voltages, it's true. But the difference is slight. It's not like they are just (isolated) linear regulators that waste the difference in voltage as heat. I would say that efficiency of the DC/DC would be a minor consideration; it's not going to affect range significantly.

Also, some DC/DCs probably have a (high frequency) transformer in their circuit, which means that they won't be chopping over the full voltage ratio. So for these units, efficiency does not depend on the voltage ratio. I suspect that the TCCharger/Elcon units are transformer based.

I would say that the convenience of wiring something like the Elcon / TCCharger unit (four wires plus fuses, bolt it down somewhere) verses these bricks (need a printed circuit board, bypass capacitors) would outweigh the slight efficiency advantage of two half-voltage bricks. But that's a personal decision.

I don't know why you say that two DC/DCs across half the pack won't unbalance it. Sure, the current is low, but if the two bricks aren't carefully balanced, you will imbalance the pack, period. Without a balancing BMS, these imbalances will likely grow over time.

When you have a 750 V pack, as we intend to (at present, it's a pair of 375 V packs in parallel), then you are stuck with two DC/DCs, since it's really hard to find a DC/DC that will chop 750 V (up to 821 V on charge) down to around 13.8 V. We'd still prefer a 750 to 14 V solution if we could find one, (and if we weren't temporarily running at 375 V).


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## cruisin (Jun 3, 2009)

Coulomb said:


> Well, it's more efficient to buck smaller ratios of voltages, it's true. But the difference is slight. It's not like they are just (isolated) linear regulators that waste the difference in voltage as heat. I would say that efficiency of the DC/DC would be a minor consideration; it's not going to affect range significantly.
> 
> Also, some DC/DCs probably have a (high frequency) transformer in their circuit, which means that they won't be chopping over the full voltage ratio. So for these units, efficiency does not depend on the voltage ratio. I suspect that the TCCharger/Elcon units are transformer based.
> 
> ...


The bricks dont really need any external support and only use 4 wires. Read the specs and you will see why the packs would not get unbalanced. If you think they will, use a 150-200v DC brick. Without a BMS you shouldnt even be in this hobby. Name a production car, either hybrid or plug-in (73) that dont have a BMS. Once again, its all about money.


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## Coulomb (Apr 22, 2009)

cruisin said:


> 1) Input voltage should be as low as possible


I disagree with this one. The efficiency of chopping one voltage to another depends on the ratio of the voltages. Those bricks may actually have transformers in them to reduce the voltage ratio anyway.

Using a 75 V rated module on half of a 144 V nominal pack is cutting things too close for me. A typical 144 V pack is 45 LiFe cells... but you can't split that evenly in half. So let's consider a 44 cell pack. At 3.2 VPC "nominal" (there doesn't seem to be much consensus on that), this would be a 141V nominal pack, or 70.4 V per half pack. But LiFe typically rest at around 3.33 VPC, so that's already 73.3V, very close to the 75 V design limit for the bricks you are recommending. Soon after charge, it's not unusual to see 3.45 VPC, so that's 75.9 V, exceeding the ratings already. During charge, you might see 3.65 VPC, which is 80.3 V, so you have to disconnect your DC/DC during charging (or risk blowing them up over time). An AC conversion (or any with regen) could see charging voltages during driving.


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## cruisin (Jun 3, 2009)

Coulomb said:


> I disagree with this one. The efficiency of chopping one voltage to another depends on the ratio of the voltages. Those bricks may actually have transformers in them to reduce the voltage ratio anyway.
> 
> Using a 75 V rated module on half of a 144 V nominal pack is cutting things too close for me. A typical 144 V pack is 45 LiFe cells... but you can't split that evenly in half. So let's consider a 44 cell pack. At 3.2 VPC "nominal" (there doesn't seem to be much consensus on that), this would be a 141V nominal pack, or 70.4 V per half pack. But LiFe typically rest at around 3.33 VPC, so that's already 73.3V, very close to the 75 V design limit for the bricks you are recommending. Soon after charge, it's not unusual to see 3.45 VPC, so that's 75.9 V, exceeding the ratings already. During charge, you might see 3.65 VPC, which is 80.3 V, so you have to disconnect your DC/DC during charging (or risk blowing them up over time). An AC conversion (or any with regen) could see charging voltages during driving.


Wrong on that one. If the DC converter rated at 40-75v see's over 80v. it will shut down and is fully isolated. I have been using these on Li-ion conversions since 2002 and have never had a problem. What problem have you had using your experience with the bricks or half brick? If you think you are going to blow them up over time with overvoltage, you havent used them nor read the specs. Here is a popular DC converter that we used on large packs up to 500v (2x250v). Never lost a single one. You can use a single up to 300v without any problems. I was also able to use them down to about 100v before they shut down.


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## Coulomb (Apr 22, 2009)

cruisin said:


> If the DC converter rated at 40-75v see's over 80v. it will shut down and is fully isolated.


So they are designed to accept over-voltage at the input? Neat. I assumed that the input range is the maximum allowed.



> ... you havent used them nor read the specs.


Quite true, and I defer to your experience with these. They sure seem like useful devices. I've been reading up on them now.


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## spdas (Nov 28, 2009)

If they have a listed output of 12v, do can the models adjust from say 12-15v?

What total wattage are u using? thanks

Francis


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## StanSimmons (Sep 3, 2011)

ElectriCar said:


> My 2008 Iota DLS55 has 12K miles on it. Yea it works but doesn't do a great job. I converted my marker lights to LED first thing. Only head and tail lights are incandescent and courtesy lights inside. I'm probably going to convert to a Vicor whenever I figure out which one to use. I have a 50 cell pack that maxes at about 173V.


This one http://www.ebay.com/itm/190617059047 (Vicor VI-251-09) will work well for your pack. They are good from 130vdc to 250vdc, they get flakey below 130v and I haven't tested higher than 250v. You can use a trim resistor (422k) to get it up to 13.2vdc. If you need more than 19A, then you can add one or more of these http://www.ebay.com/itm/200690550969 (Vicor VI-B51-02) to bump it another 19A each.

These Vicor modules were special order for an Azure Dynamics project. Lots of good info can be found here: http://www.diyelectriccar.com/forums/showthread.php/dc-dc-converter-44048p2.html?highlight=Vicor


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## StanSimmons (Sep 3, 2011)

cruisin said:


> Wrong on that one. If the DC converter rated at 40-75v see's over 80v. it will shut down and is fully isolated. I have been using these on Li-ion conversions since 2002 and have never had a problem. What problem have you had using your experience with the bricks or half brick? If you think you are going to blow them up over time with overvoltage, you havent used them nor read the specs. Here is a popular DC converter that we used on large packs up to 500v (2x250v). Never lost a single one. You can use a single up to 300v without any problems. I was also able to use them down to about 100v before they shut down.


I hope you aren't using the VI-B51-02 by itself, it is designed to run as a booster (hence the "B") to the VI-251-09.

I've seen lots of flakiness and noise below 130vdc on the AZD Vicor bricks, and I don't recommend running them below 130vdc. I can't easily test them above 250vdc, so I have no comment about your experience at 300vdc... they are rock solid at 250vdc.


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## Coulomb (Apr 22, 2009)

spdas said:


> If they have a listed output of 12v, can some models adjust from say 12-15v?


Yes, there are nominal 15 V modules, which can be adjusted at least +- 10% (so at least 13.5 to 16.5 V). The problem is that these modules are expensive and difficult to obtain, except from Ebay, so you tend to be stuck with what is available surplus. For whatever reason, 12 V modules seem to be more available from Ebay than 15 V modules. As far as I know, anyway.


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## ElectriCar (Jun 15, 2008)

StanSimmons said:


> This one http://www.ebay.com/itm/190617059047 (Vicor VI-251-09) will work well for your pack. They are good from 130vdc to 250vdc, they get flakey below 130v and I haven't tested higher than 250v. You can use a trim resistor (422k) to get it up to 13.2vdc. If you need more than 19A, then you can add one or more of these http://www.ebay.com/itm/200690550969 (Vicor VI-B51-02) to bump it another 19A each.
> 
> These Vicor modules were special order for an Azure Dynamics project. Lots of good info can be found here: http://www.diyelectriccar.com/forums/showthread.php/dc-dc-converter-44048p2.html?highlight=Vicor


Stan thanks so much for the info! Saved me a lot of digging and second guessing. So how is it that you connect the resistor to tweak the output voltage? Is it designed for that?


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## spdas (Nov 28, 2009)

StanSimmons said:


> I hope you aren't using the VI-B51-02 by itself, it is designed to run as a booster (hence the "B") to the VI-251-09.


How do you run it as a booster? Just in parallel with the v1-251-09?

thanks
francis


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## ElectriCar (Jun 15, 2008)

Nevermind. Just followed your link and got all my answers.


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## StanSimmons (Sep 3, 2011)

ElectriCar said:


> Stan thanks so much for the info! Saved me a lot of digging and second guessing. So how is it that you connect the resistor to tweak the output voltage? Is it designed for that?


Yes it is designed for up to a +10% trim up. See pages 9 and 10 of the following pdf for details.

http://cdn.vicorpower.com/documents/applications_manual/DesignGuideAppsManual_200J00.pdf


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## StanSimmons (Sep 3, 2011)

spdas said:


> How do you run it as a booster? Just in parallel with the v1-251-09?
> 
> thanks
> francis


Connect the Gate Out of the VI-251-09 to the Gate In of the VI-B51-02. See page 13, Figure 7-5, for details.

http://cdn.vicorpower.com/documents/applications_manual/DesignGuideAppsManual_200J00.pdf


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## Coulomb (Apr 22, 2009)

StanSimmons said:


> Connect the Gate Out of the VI-251-09 to the Gate In of the VI-B51-02. See page 13, Figure 7-5, for details


They don't seem to say how to VI series drivers and boosters if these modules are connected across separate half packs. I image that they can be transformer connected; perhaps using a transformer that Vicor themselves make. This would guarantee fairly good power balance.


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## StanSimmons (Sep 3, 2011)

Coulomb said:


> They don't seem to say how to VI series drivers and boosters if these modules are connected across separate half packs. I image that they can be transformer connected; perhaps using a transformer that Vicor themselves make. This would guarantee fairly good power balance.


In your case, with a 750vdc pack, you would tap off of the pack in 4 places to feed the 4 Vicor bricks. Assuming you have 236 cells in your 750vdc pack, you would tap off at cell 59, 118, 177, and 236. 

You would have 1 VI-251-09 and 3 VI-B51-02 bricks each with a 188vdc nominal feed. You would connect the gate out/gate in connections in a daisy chain, so that the bricks would share the load and not unbalance the pack. The outputs would be ganged together as in figure 7-5 of the pdf listed above.

ETA: I have not tested this configuration, but according to the pdf, this should work.


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## Coulomb (Apr 22, 2009)

StanSimmons said:


> In your case, with a 750vdc pack, you would tap off of the pack in 4 places to feed the 4 Vicor bricks.


Assuming we could find them at a reasonable price.

[ Edit: duh! The models already mentioned in this thread are suitable. ]



> You would have 1 VI-251-09 and 3 VI-B51-02 bricks each with a 188vdc nominal feed. You would connect the gate out/gate in connections in a daisy chain, so that the bricks would share the load and not unbalance the pack. The outputs would be ganged together as in figure 7-5 of the pdf listed above.


But my point was, presumably you can't connect them directly when the Vin- terminals are nominally 188 V apart. The gate out of one module is referenced to its own Vin-, but the gate in of the next in the chain is referenced to *its* Vin-, which is 188 V away. Directly connecting them would be a good way to blow them up, surely. Or at least blow up the gate in circuitry, rendering them useless anyway.


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## StanSimmons (Sep 3, 2011)

Coulomb said:


> Assuming we could find them at a reasonable price.


ebay... US$25 shipped, US$100 for 5. That is for the US, I'm not sure what they would charge for AU shipping.


Coulomb said:


> But my point was, presumably you can't connect them directly when the Vin- terminals are nominally 188 V apart. The gate out of one module is referenced to its own Vin-, but the gate in of the next in the chain is referenced to *its* Vin-, which is 188 V away. Directly connecting them would be a good way to blow them up, surely. Or at least blow up the gate in circuitry, rendering them useless anyway.


You may be right on that. You may have to get 4 of the VI-251-09 bricks and not use the gate circuits. It won't be as efficient but it won't let the smoke out either.


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## ElectriCar (Jun 15, 2008)

OK another question. What happens if you draw more amps from your system than the Vicor can supply? Will it try and deliver too much and smoke or will it current limit at the rated amps until the volts drops too low then shut down or what?


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## StanSimmons (Sep 3, 2011)

ElectriCar said:


> OK another question. What happens if you draw more amps from your system than the Vicor can supply? Will it try and deliver too much and smoke or will it current limit at the rated amps until the volts drops too low then shut down or what?


Page 7 says:


> STRAIGHT LINE CURRENT LIMITING
> The VI-/MI-200 modules with output voltages greater
> than 5 V, 2 V (VI-/ MI-200 only) and all VI-/MI-J00
> modules incorporate a straight-line type current limit.
> ...


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## bruceme (Dec 10, 2008)

There seems to be a whole industry around fixing, refurbishing and re-selling broken Vicors. They are very expensive, does anyone have anything more than anecdotal evidence that they perform better and last longer than an off-the-shelf DC-DC?

-Bruce

p.s. I'm on second Iota since buying my BMW two years ago.


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## Coulomb (Apr 22, 2009)

bruceme said:


> There seems to be a whole industry around fixing, refurbishing and re-selling broken Vicors.


Huh? How do you fix a Vicor? They're potted / sealed.

If you are referring to all the cheap Vicors on Ebay, I don't believe that these are refurbished. (They all claim to be new (as in unused), old stock). I assume that these are from liquidation sales: companies buy hundreds of them, go broke, and those not yet put into manufactured goods get sold cheaply by the liquidators. Or they are old models from the manufacturer, obsoleted by newer models.


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## ElectriCar (Jun 15, 2008)

bruceme said:


> There seems to be a whole industry around fixing, refurbishing and re-selling broken Vicors. They are very expensive, does anyone have anything more than anecdotal evidence that they perform better and last longer than an off-the-shelf DC-DC?
> 
> -Bruce
> 
> p.s. I'm on second Iota since buying my BMW two years ago.


What size did you buy, the 35? If that's the case it's likely the reason for the failure. My truck with most everything on draws about 45A. Mine is a 55A unit and I only run the fan blower on low & have LED marker lights installed is likely why mine has lasted so long. Hardly ever go over 50% output I suspect.


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