I have sort of a weird question I'm hoping folks here can help with. Have searched other questions but not found a similar-enough one that applies.

I have a large mechanical system which travels over a rail. The rail has a set of powered contact strips. Each strip has a carbon brush positioned directly over it. (the brushes have tension springs in them to maintain contact). As the system travels along this rail, the brushes transfer DC voltage to a battery charger, which charges a 24V battery bank on the system, and between the battery and the charger, the loads pull current as needed. The charger, battery and loads are connected in parallel.

On a recent on-site visit to use the system, the brushes broke contact with the charging strip for a fraction of a second, when contact was re-established, the charger input capacitor and other electronics blew. I think the in-rush current from the high draw + disconnect/reconnect was the cause, as prior to this the system worked well with no issues for a month.

Upon investigation of a replacement, I found that the charger is no longer available. My question now becomes what to replace it with. I am considering a regulated DC power supply, but am curious what others think may be a better solution.

I figure there are 2 problems with this system. The incoming DC current is probably noisy due to the brush pickups and potential for disconnect. Secondly, somehow, the batteries should be charged. I figure I could simply run the input voltages at ~ 28VDC, just as a vehicle electrical bus does, keeping the batteries float charged. The issue I see here is handing the batteries dirty signal may be a bad idea. My second idea was to use something like a mean well DC-DC voltage regulator, and still float-charge the batteries, but basically configure the output of the DC regulator at 2-3V over the battery voltage (say 27V or so), and expect that the converter can absorb the input noise and be nicer to the batteries and downstream loads.

I have investigated using solar chargers, but having discussions with tech reps at companies who distribute such systems leads me to conclude this is not the way to go. Is there a different/better option for something like this?

simple diagram

(Basic Specs)


1 Answer 1


It looks like your system has total power requirement of about 300 watts (based on input of 29V and 9A). A properly designed DC-DC converter with output set for 24V SLA battery charger should not have had any problems with a noisy or intermittent connection, but apparently the one you had failed under these conditions.

I don't know what experience you have with circuit design and building, so I will assume you would rather purchase something that will just work. I would suggest that you purchase a simple 300W inverter designed for 24V nominal battery input (probably 22-30 VDC), and 120 or 240 VAC output, like this.

Then connect the AC output to a charger designed for two 24V SLA batteries or two chargers for 12V batteries. That will make sure the batteries will be charged with the proper limited current and float voltage profile.

  • \$\begingroup\$ Interesting solution! I considered the notion of converting to AC as there are so many AC-> DC charger options available, but figured there was some obvious better answer I'd missed. Thanks for proposing this, I'll likely go this route! \$\endgroup\$
    – ARC
    Aug 4, 2022 at 18:05

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