[ausev] Simple charger, was ROI on sustainable technologies

Thu Aug 14 11:30:27 GMT 2008

Chris:

Just an idea: if you need higher DC voltages at minimum cost, check the 
voltage multiplier circuit in Wikipedia. You can get 230 V DC output 
from 115 V DC input with only two diodes and two capacitors. The only 
question is current. You will need fairly large capacitors, but this is 
a very elegant and efficient solution!

If feasible (A long time ago, I only build small power versions) I 
suggest that you set the current by selecting the values of the 
capacitors. Adding or removing capacitors in parallel will let you 
adjust the current.

Michael Bonard
Washington, DC

Chris Robison wrote:
> You're right; I wasn't thinking about how much higher peak voltage is 
> versus RMS.
>
> Trojan recommends a charging voltage of 2.43Vpc for their batteries at 
> 80F, which for a 144V pack would mean a voltage of 175.2V at the end of 
> the charge. However, the boost provided by the variac would more than 
> cover this small discrepancy, and even without it, you'd be able to 
> "mostly" charge the batteries though you'd have no control over current.
>
> Not needing a separate boost transformer certainly makes the project 
> more practical, in the sense of getting something working quickly on the 
> cheap.
>
>   --chris
>
>
> Rob wrote:
>   
>> Chris,
>>
>> Erik and I talked about this a while a ago - he suggested that because 120
>> VAC is RMS, the actual peak voltage is 170 volts.  Since this is a minimal,
>> emergency charger then I could take advantage of the >144 volts part of the
>> waves to charge the battery.  No boosting would be required.
>>
>> Rob
>>
>> RMS: http://www.ee.unb.ca/tervo/ee2791/vrms.htm
>>
>> -----Original Message-----
>> From: ausev-bounces at austinev.org [mailto:ausev-bounces at austinev.org] On
>> Behalf Of Chris Robison
>> Sent: Wednesday, August 13, 2008 3:14 PM
>> To: AustinEV News Announcements and General Discussion
>> Subject: [ausev] Simple charger, was ROI on sustainable technologies
>>
>>
>> A dumb charger is often implemented with a variac, a bridge rectifier, 
>> and an ammeter and voltmeter. It has no brains, so you have to "be the 
>> brains" in the sense that you'll need to control voltage with the variac 
>> knob to prevent the batteries from drawing too much current. And as the 
>> pack charges, you may have to move the dial to maintain current and/or 
>> transition from current-limited to voltage-limited charging, as the 
>> batteries get full. The higher your pack voltage, the more likely you'll 
>> have to do this.
>>
>> Most variacs (variable transformers) have some boost on the high end of 
>> the dial, but I haven't seen one that will produce more than 140VAC on 
>> 120VAC input so you'll probably also need a boost transformer if you 
>> want to go that route.  I'd suggest getting a 240VAC rated variac, if 
>> your intended charging context would allow for it.  240VAC variacs are 
>> much harder to find used (there aren't any on eBay as I write this) but 
>> they can be found. I bought one a couple years ago for peanuts.
>>
>>   --chris
>>
>>
>>
>>
>> Roy Holder wrote:
>>   
>>     
>>> At 10:54 AM 8/13/2008 -0500, you wrote:
>>>   
>>>     
>>>       
>>>> Scott,
>>>>
>>>>  I love driving the RAVolt and am always glad that I put in the 
>>>> effort to create it.
>>>>
>>>>  Batteries are stable @ a comfortable 20 mile range (meaning I 
>>>> don&#39;
>>>> No leaks.
>>>>
>>>> I&#39;d like to build an oh-sh!t charger: one w/o any brains that 
>>>> just dumps rectified 120 RMS VAC into my 144 VDC pack while I monitor 
>>>> it- does anyone have some ideas or plans?
>>>>     
>>>>       
>>>>         
>>> The 'no brains'  charger I think would quiclky cause a breaker trip. 
>>> you would typically be limited to 16 to 18 amps on the 120vac side w/o 
>>> power correction(more brains..), maby less depending or the state of 
>>> the core and coil inverter.
>>>
>>> I use a russco 120vac charger as my main charger.  I specifically 
>>> chose the 120vac version so I could charge anywhere.  It works real 
>>> nice and I can adjust the amps to match what is available.  I know it 
>>> cost a lot more than a basic rectifier, but I think the batteries are 
>>> worth it.
>>>
>>> My trojan J150 batts are 2 years old now and I still drive 20 miles a 
>>> day, with accasional trips of 25 to 28.  I hope you have as good a use 
>>> out of your batts as mine.
>>>
>>>
>>>   
>>>     
>>>       
>>>> Rob
>>>> & EValbum 995
>>>>
>>>>
>>>> On Tue, Aug 12, 2008 at 4:03 PM, Wieser Scott <Scott.Wieser at irs.gov>
>>>>       
>>>>         
>> wrote:
>>   
>>     
>>>>       & proactive. Also, how is  the ravolt&#39;s batteries doing?  
>>>> We&#39;re all in this  together,   Scott  
>>>>  No virus found in this incoming message. Checked by AVG - 
>>>> http://www.avg.com  Version: 8.0.138 / Virus Database: 270.6.2/1609 - 
>>>> Release Date: 8/13/2008 6:43 AM 
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