How to control current inrush for an HVAC compressor

[Vimes]

Have a question for the HVAC pros here.

https://www.vmacs.net/products/red-d...t-e-6100-0-12p

This is the unit in question. 12VDC air conditioning system, requires 100 amps to operate. That means it's likely seeing a 200A inrush current each time it clicks on, then a sudden 100 amp overload each time it shuts off and its load disappears. I know the battery can handle the short overload when the unit shuts off, but the inrush current is going to be a problem. Can this be controlled in any way, like perhaps with a capacitor and if so, what would be recommended? This is a system used on heavy equipment, but can be used on a tractor cab as well.

Please limit discussions to this unit, not possible better solutions unless there's an R134a HVAC system out there I've not come across that operates on 12VDC and has at least 12,000BTU of cooling power (this one creates 11,900BTU of cooling power.) This unit suits my needs perfectly once I find a solution to the current inrush problem.

[Hotwire]

Give these guys a call, used them for industrial ac motors before, might have a solution for you.

https://www.ametherm.com/inrush-current/

[Vimes]

Thanks, have them saved. Still hoping an AC tech will chime in here though. I don't know if there's HVAC-specific stuff involved or not.

[Big_KID]

Sounds more an electrical supply issue than HVAC issue. I believe you are on the right path with adding a capacitor or bank of. In order to size the cap/bank, the load amps and start frequency would be needed to insure the energy capacity need in the cap/bank and adequate charging rate/time for such cap/bank. You may want to consult a mobile audio forum as they deal with the same issue on a much faster charge/discharge rate for high end audio systems. Multiple battery systems are used for this as well which may be more feasible option for this application.

Some additional thoughts I had...
Does your alternator have the capacity for such a large load addition?
Have you spoken with vmacs about this? I would think such an unit would already have a capacitor designed into it to help with inrush. You may just need to ensure you have the proper generating capacity for the 60-100A load specified.

[Vimes]

Sounds more an electrical supply issue than HVAC issue. I believe you are on the right path with adding a capacitor or bank of. In order to size the cap/bank, the load amps and start frequency would be needed to insure the energy capacity need in the cap/bank and adequate charging rate/time for such cap/bank. You may want to consult a mobile audio forum as they deal with the same issue on a much faster charge/discharge rate for high end audio systems. Multiple battery systems are used for this as well which may be more feasible option for this application.

Some additional thoughts I had...
Does your alternator have the capacity for such a large load addition?
Have you spoken with vmacs about this? I would think such an unit would already have a capacitor designed into it to help with inrush. You may just need to ensure you have the proper generating capacity for the 60-100A load specified.

Yes, the alternator will have more than enough juice to supply it. My concern is that this compressor cycling will be slamming a 100 amp load on and off the electrical system every X number of minutes. That can't be good for the rest of the stuff on there. The unit will also be mounted next to the battery, so there is that. I may double up on the batteries for this if necessary but I'd really rather find a solution that protects my electrical system from the compressor, and protects the compressor from itself. Can you recommend any audio forums I can try? I don't frequent them, since my audio needs are pretty much limited to Alpine head unit with CD and flash drive, 4 speakers and a powered subwoofer. When you have tinnitus, high dollar systems sound the same as cheap ones so you aren't as interested in putting money into them.

I sent an email to Red Dot about it, waiting on a response. I didn't see a capacitor on their schematic. My reading on the subject indicates that such devices used to be common but HVAC manufacturers started leaving them out to save money, and probably to prompt earlier replacements since slamming a motor with a huge current isn't good for the motor either. The reading comes from HVAC tech boards, but they're all talking about house systems so they're AC, not DC.

[Vimes]

OK, this issue is now resolved. I finally heard back from the factory, and the part of the unit in question only runs 60A, not 100A. It would only be 100A if I bought their complete standalone unit and I'm just using the compressor for an existing system. Plus, their compressor is set up with a built-in 10 second soft start, so this isn't going to be a negative impact at all.

Thanks for the advice on this, folks. While I didn't need the advice in the end, it did give me a pathway to a solution that I could have pursued.