Keep at it.
If you design your own, you will be able to change it later for a different battery chemistry.
I have found most cheap chargers tend to overcharge batteries.
With a microcontroller monitoring voltage, temp, etc you should be able to make your batteries last longer.
Mark
From: oak <oak_box@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Tuesday, January 7, 2014 5:29:24 PM
Subject: Re: [Electric Boats] RE: Charger design options
If you design your own, you will be able to change it later for a different battery chemistry.
I have found most cheap chargers tend to overcharge batteries.
With a microcontroller monitoring voltage, temp, etc you should be able to make your batteries last longer.
Mark
From: oak <oak_box@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Tuesday, January 7, 2014 5:29:24 PM
Subject: Re: [Electric Boats] RE: Charger design options
Bob,
Ultimately, you are probably correct.
I've been tinkering on my own because I couldn't find a "reasonably priced" charger that can handle everything I want:
Able to charge 12, 24, or 48V battery banks
Able to customize the charging profile
Cheap enough that I could afford one for each bank I want to use...
Of course, by the time I get done "tinkering", I'll probably have spent as much money, and far more time, than if I had just gone out and bought several really good chargers...
But, I guess that's what tinkerers do. :)
From: Bob Caulk <bob_caulk@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Tuesday, January 7, 2014 5:08 PM
Subject: Re: [Electric Boats] RE: Charger design options
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Tuesday, January 7, 2014 5:08 PM
Subject: Re: [Electric Boats] RE: Charger design options
It seems that what you are working on here IS a power supply of sorts; As you are finding out, it seems simple but as things are thought through, there is a fair amount of complexity in the details. With my electrical engineering background i could design my own power supplies, or battery chargers, but I generally choose to save both time and money and purchase one.
On Tuesday, January 7, 2014 2:37 PM, oak <oak_box@yahoo.com> wrote:
Kevin,
Yes, in theory, that makes perfect sense.
I could also envision setting up something like a 555 timer chip with a variable resistor that would let me set the pwm manually to match the voltage (and thus current) needed to charge the battery.
To automate it, I guess I could have the Arduino generate a PWM wave form to drive a power transistor feeding the battery. I could then feed the charger (source) voltage and the battery (load) voltage into the Arduino, and let it use that information to calculate the correct value for the PWM duty cycle. Actually, it might not be too hard - rather than trying to do it in a truly analog manner, I could read the battery voltage, average it for a bit to get a good value, and set the PWM from a table of several values.
It would be nice if I knew how to design power supplies. Though if I had THAT skill, I probably wouldn't be as good at writing code, or building boats, or something - seems like most people aren't good at EVERYTHING. :)
I wish there was a simple book out there with easy to follow instructions for "how to design a step up / step down power supply".
I know they've got ICs that are specifically designed for that job. But I haven't yet seen a good tutorial for how to design your own high wattage power supply.
From: Kevin Pemberton <pembertonkevin@gmail.com>
To: electricboats@yahoogroups.com
Sent: Tuesday, January 7, 2014 3:43 PM
Subject: Re: [Electric Boats] RE: Charger design options
To: electricboats@yahoogroups.com
Sent: Tuesday, January 7, 2014 3:43 PM
Subject: Re: [Electric Boats] RE: Charger design options
Current is easy to limit. Just a slight drop in voltage will do the job(ohms law dictates that for us).
If I were to design a simple charger I would start with 15 volts per 12 volts of battery string. I would then use a pwm circuit to regulate the voltage down for the battery charge resistance required to limit the current. I hope that makes sence to you.
If I were to design a simple charger I would start with 15 volts per 12 volts of battery string. I would then use a pwm circuit to regulate the voltage down for the battery charge resistance required to limit the current. I hope that makes sence to you.
Kevin
On Jan 6, 2014 10:01 AM, "oak" <oak_box@yahoo.com> wrote:
Gary,Thank you very much for the reference! I hadn't seen that one yet....This is the only one I've seen so far that has the current limit. Very cool.A little more expensive than the other units I've looked at, but still not bad.I only wish I could get this from a distributor in the states. And that there was a little better documentation for it.... (though, "who reads directions anyway?!").JohnFrom: Gary Vander Hart <gvanderhart@midco.net>
To: electricboats@yahoogroups.com
Sent: Saturday, January 4, 2014 9:35 PM
Subject: Re: [Electric Boats] RE: Charger design options
The rating on the transformer is intended to inform the design. In other words, the transformer is not limited to the number of amps it will provide, the design must limit the number of amps that the transformer will draw or else the transformer will be damaged.If the design does not limit the current, I have no doubt that a deeply discharged battery will present a load that will burn out the transformer. Hopefully, the design also includes AC fuses which will immediately open.I noticed that Amazon also has a DC to DC converter that permits a current limit setting.Gary Vander HartFrom: oakSent: Saturday, January 04, 2014 8:42 PMSubject: Re: [Electric Boats] RE: Charger design optionsIn either case (using the transformer, rectifier and filter cap - or using the booster), the transformer is limited to the number of amps it will provide.I guess the next major question is:If I connect the "power supply" that should only put out around 4-6A to the battery, will I burn up the power supply if the battery is deeply discharged?The "correct" answer (at least for lead batteries) would be to use a constant current source - but this was never done in the old days. Maybe a current limit resistor, probably just a transformer and a diode.I have no doubt that the current will ultimately be limited. But if the battery voltage is relatively low, I'm wondering if I will go through power supplies / transformers quickly?From: "gvanderhart@midco.net" <gvanderhart@midco.net>
To: electricboats@yahoogroups.com
Sent: Saturday, January 4, 2014 10:41 AM
Subject: [Electric Boats] RE: Charger design optionsI think that either scheme will work. If 24V rectifier and filter, you should get 30V to 34V DC. If 12V rectifier and filter followed by a DC to DC converter, you can more precisely adjust the output voltage. In either case, the challenge will be to limit the current to around 5A. If the voltage is adjustable, then monitor the current and set the voltage appropriately. If the voltage is not adjustable, then a current regulation circuit is needed. I would search for a simple series (high power) FET circuit or buy a regulator intended for a solar or wind charging system. This would work better for LiFePO4 batteries since they do not have the bulk-saturation-float charging requirements that accompany lead acid batteries.Gary Vander Hart
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