Oznog
Active Member
I need to make a power supply that will work with my car's high output (140 amp) alternator to charge an AGM battery, which has a max voltage of 14.22v whereas my alternator puts out 14.6v which is still needed for the main flooded plate battery. Anything above 14.22v will cause gassing and permanently degrade the AGM battery. It will probably charge at like 30 amps but the AGM battery may also be loaded with up to a 100 amp load.
First off, this can't be done with on/off PWM switching. Please don't bring this up. I'm just trying to save us some time here.
I'm considering a MOSFET switch which can dissipate the 50 watts and handle 130 amps in a linear mode. But I'd much rather do a step-down switching buck converter and not handle that kind of heat in the MOSFET. This is a lot of heat. In fact, if the AGM battery is low and the regulator is in current limit mode, there may be a much larger voltage gap. We could be well into 100's of watts in some cases for a linear reg.
I did have an idea where the heavy external loads could be switched off the battery and onto the alternator when running, but the load really needs the filtering the battery provides (alternator is just rectified 3-phase) and may need the battery's enormous current capabilities to start up very heavy loads too.
My problem here is I don't know of a buck inductor off the shelf capable of this amperage. I've got some big toroids here, the wire on them won't even take it. Skin effect won't allow me to put big cable on here. Nor will the stock insulation on my thick cable create tight coupling. I know about using multiple solid windings to get around skin effect but I'm still going to need a LOT of core and a lot of wire.
Any ideas here on how I can get ahold of such a large inductor? Or make one? I had some neat ideas about taking a big core and wrapping the copper braid used for ground straps or solder removal though insulation is an issue. It was one idea.
I know I can put inductors in series, but do they parallel? When I looked at the issue, it seems like the warmer inductor will have a lower inductance which means its peak current is higher each cycle which could create a runaway condition.
First off, this can't be done with on/off PWM switching. Please don't bring this up. I'm just trying to save us some time here.
I'm considering a MOSFET switch which can dissipate the 50 watts and handle 130 amps in a linear mode. But I'd much rather do a step-down switching buck converter and not handle that kind of heat in the MOSFET. This is a lot of heat. In fact, if the AGM battery is low and the regulator is in current limit mode, there may be a much larger voltage gap. We could be well into 100's of watts in some cases for a linear reg.
I did have an idea where the heavy external loads could be switched off the battery and onto the alternator when running, but the load really needs the filtering the battery provides (alternator is just rectified 3-phase) and may need the battery's enormous current capabilities to start up very heavy loads too.
My problem here is I don't know of a buck inductor off the shelf capable of this amperage. I've got some big toroids here, the wire on them won't even take it. Skin effect won't allow me to put big cable on here. Nor will the stock insulation on my thick cable create tight coupling. I know about using multiple solid windings to get around skin effect but I'm still going to need a LOT of core and a lot of wire.
Any ideas here on how I can get ahold of such a large inductor? Or make one? I had some neat ideas about taking a big core and wrapping the copper braid used for ground straps or solder removal though insulation is an issue. It was one idea.
I know I can put inductors in series, but do they parallel? When I looked at the issue, it seems like the warmer inductor will have a lower inductance which means its peak current is higher each cycle which could create a runaway condition.
