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 Hart
From: oak
Sent: Saturday, January 04, 2014 8:42 PM
Subject: Re: [Electric Boats] RE: Charger design options
In 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 options
To: electricboats@yahoogroups.com
Sent: Saturday, January 4, 2014 10:41 AM
Subject: [Electric Boats] RE: Charger design options
I 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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