Don'tt worry, pwm is nothing other than two time bases. If you stick with a transformer that will offer charging voltage and use the pwm to regulate current (use a thermistor to monitor transformer temp). That will offer a variable time base to establish duration of reset clock based on temp of transformer and should mot need a smart control for such a system to save problems with the transformer.
The reason I would build my own is so I could run my controller under way with supplement power and not worry what might be happening to my charger.
Think about it this way. Motor protection uses a thermal switch to break contact if the motor gets above design temp.
Kevin
On Jan 7, 2014 3:37 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
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.KevinOn 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?!").John
From: 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
__._,_.___
| Reply via web post | Reply to sender | Reply to group | Start a New Topic | Messages in this topic (19) |
.
__,_._,___
No comments:
Post a Comment