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Old 10-16-2010, 11:36 AM
mechman600 mechman600 is offline
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Default Cheap charging options

I am planning my first EV project using a '78 Honda CB400T. It will be 48V with a Mars/Etec style motor. I'm hoping for a 12-15 mile range and a top speed of 50 mph for my commute. My question is about charging. I know using four separate cheaper 12V chargers can work well to keep everything balanced on a low budget, like in this thread:
http://www.diyelectriccar.com/forums...allel+charging

But, what about switching from series to parallel for charging? For driving you would use series for 48V. But for charging you would open the circuits between batteries and reconnect in parallel with a smaller charging circuit. This would keep the batteries perfectly balanced using one 12V higher amp charger, would it not? For the sake of space on a motorcycle, one large charger would take up less space than four smaller ones; plus, it would cost less. Has this been attempted before?

Thanks in advance!
James
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Old 10-16-2010, 12:28 PM
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dtbaker dtbaker is offline
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Default Re: Cheap charging options

hooking/unhooking multiple chargers each night, or switching battery connections, sounds like an incredible waste of time versus the cost of getting a decent production charger. Charging in parallel of one cheap 12v charger would take forever anyway as you can't pump many amps to the batteries.

save your money and time and buy a decent charger.
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Old 10-16-2010, 12:57 PM
mechman600 mechman600 is offline
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Default Re: Cheap charging options

Thanks for the advice. What would be the best charger for 48V X 55ah?
I was thinking of putting a battery disconnect between each battery in the traction circuit and switching the parallel charge circuit on with relays. So to charge, switch the 3 battery disconnects off (between the 4 batteries) and flip the "charge" switch that connects the batteries in parallel with relays to the 12V charger. I have all night to charge it up, and with four 55ah batteries I would only need to charge at 10A anyway, as far as I know. I could use a 48V 10A charger (the golf cart chargers I've seen are 13A), or four 10A 12V chargers, or one 40A 12V charger wired in parallel.
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Old 10-17-2010, 01:08 AM
mechman600 mechman600 is offline
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Default Re: Cheap charging options

Today I learned about vari-bad-boy chargers, and other similar chargers. These things appeal to me because of their price. I am on a ridiculously tight budget. I understand the risks and attention required while charging, but I'm going to do it anyway.

Instead of buying a variac that is heavy and pricey, has anyone tried making a manually controlled charger out of a 1000W dimmer switch and a bridge rectifier? A dimmer switch is tiny and light - much more appealing for a motorcycle. And 1000W will be lots enough for my purpose. My second question is: at 48V and 10-12A, how big of capacitor will I need (if at all) after the rectifier to smooth things out enough for charging? Will this work or am I out to lunch?
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Old 10-17-2010, 04:23 AM
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Default Re: Cheap charging options

I did try using a multi pole break before make rotary switch on my 48v tractor to switch the reading from a volt meter to read individual battery voltages and the pack voltage.
I figured that if it worked then I could use a similar set up to switch for charging voltage so that I could drive in series and charge in parallel.

After a flicks of the switch it shorted and blew up.

The idea was sound but the switch needed to be a much higher rating with bigger gaps between the break before make wiper.
Better still would be a switch frame with separate switch units stacked up.
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Old 10-17-2010, 07:15 AM
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Default Re: Cheap charging options

After all your troubles of figuring out how to do this and the parts to make it work and the experimenting to make it work you could just go out and buy a single charger new that you don't have to think about. Just plug it in and forget about it. I use a Quickcharge Select-A-Charge 96 volt charger and it works perfect. Not overly expensive and quiet. It shuts down after its done charging. Not the best on board charger for a bike but it would be fine for a home charger. It would charge your pack easy. I think it's like 12 amps. Got mine for $200 bucks.

Why go to all the trouble of doing the switching and and such when you could just plug it in and forget about it. I thought that was one of the best things about an electric vehicle. Just plug it in and go about your business. No worries. No hassles, No headaches, No problems.

Pete
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Old 10-17-2010, 10:57 AM
mechman600 mechman600 is offline
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Default Re: Cheap charging options

You are right...for $200 why would I bother. I guess that's my biggest problem: I like to tinker too much. Where did you get your Select-A-Charge charger? I need something that fits on my bike because I need to charge it at work as well as at home.
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Old 10-17-2010, 12:24 PM
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Default Re: Cheap charging options

In regards to having to disconnect all the batteries in the string (go from series to parallel) for charging, if you are using multiple 12V chargers and they have isolated outputs, then this is not necessary. By isolated, I mean there must be no electrical connection between the DC output side and the AC input. If this is the case, then you can hook one to each of your 12V batteries while they are still in series with each other without worry.

You can get multi-bank isolated 12V chargers for boats, etc, I know you can get ones with four chargers (48V) in one box. Perhaps that is the model you are talking about above, not sure. So essentially it would be "one" charger though electrically it would manage each 12V battery separately.

As variac chargers go, they can be very cheap to build if you can get ahold of an appropriate variac cheaply. They work best when the line voltage going into the variac is similar to the battery voltage (because you get the most power that way) but will output anywhere from zero to the maximum voltage you can safely wire the variac for given input voltage, which is at least 100% and commonly 125% of line voltage. So if you were to find a 20A, 120v rated variac (which weighs about 25lbs) you could charge 48V at about 20A. Something to consider would be a stepdown transformer in addition to the variac. For example, a 2:1 stepdown in addition to the variac would increase your charging capability to 40A instead of 20A and you would still be within the limits of the variac and a 20A, 120v household circuit. Of course we are talking about a stationary charger now.

Down side of any kind of bad boy/variac charger is it is easy to over/under charge and possibly damage something. You will need to keep a close eye on things while it is charging. It is doable, I've been running off my variac charger for a couple of months since my russco charger broke down again while I work on reconfiguring and upgrading the charging circuits and related stuff on the car to take a 240V-input Manzanita.

Good luck.
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Old 10-17-2010, 01:29 PM
mechman600 mechman600 is offline
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Default Re: Cheap charging options

Quote:
Originally Posted by madderscience View Post
In regards to having to disconnect all the batteries in the string (go from series to parallel) for charging, if you are using multiple 12V chargers and they have isolated outputs, then this is not necessary.
Thanks for the advice. For curiosity sake, if you charge four batteries in parallel @ 12V+, as opposed to in series @ 48V+, will the parallel circuit connecting them all make them properly balance while charging? In my head, they should. The advantage I see here is: a) a balanced charge, and b) no need for a charger on my bike. I could use the 12V 60A charger at work (I work in the shop at a commercial truck dealership) and have my own 12V charger at home.
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Old 10-17-2010, 04:20 PM
gottdi
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Default Re: Cheap charging options

Quote:
Originally Posted by mechman600 View Post
You are right...for $200 why would I bother. I guess that's my biggest problem: I like to tinker too much. Where did you get your Select-A-Charge charger? I need something that fits on my bike because I need to charge it at work as well as at home.
Tinkering is a decent learning option but for practical purposes just get what you need. Since you really don't build things like this why go through the hassle. Once your machine is up and running if you decide to build a charger to better suit your needs then by all means do so. But make sure you have a good decent setup first. It does not have to be perfect but it does need to be functional and one that won't destroy what you have done.

I got my new charger from someone wanting to upgrade before they even used this one. It is perfect. Works perfect and if you really needed to take it with you it is designed as an on board charger. A car just happens to have more room. I am sure you can find a decent smart charger that will do the whole pack at once for a decent price that will be small enough and light enough for your bike.

Pete
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