Looking for advice on DC-DC converters

What you want is a lead-acid battery charger that works over the voltage range of your traction battery, not a DC-DC converter.

Maybe a solar charge controller would work ?

Couple of examples from a quick search on AMZ :

First one is limited to 55V, may be a bit too low for this application (needs to handle up to 58.8V for 14S).
Second one can take up to 100V. I am sure there are many others out there.

I'n not sure he wants one with MPPT...unless MPPT can be shut off.

remy_martian said:

I'n not sure he wants one with MPPT...unless MPPT can be shut off.

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I was wondering about that... would it matter ? His traction pack won't drop the voltage even when the charge controller is pulling maximum current.

All depends on whether cowboys wrote the firmware or not.

You'd think they would throw fault codes, if they can't initially map MPPT or if the array is unresponsive, if MPPT can't be disabled.

This is all you need! is only $30 and is normally used in golf carts.

EV-Caveman said:

This is all you need! is only $30 and is normally used in golf carts.

DC 48V Step Down to 12V 30A 360W Voltage Reducer Converter Regulator Waterproof | eBay

Find many great new & used options and get the best deals for DC 48V Step Down to 12V 30A 360W Voltage Reducer Converter Regulator Waterproof at the best online prices at eBay! Free shipping for many products!

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I actually picked one of these up, but the Ebay listing specifically said not to use it to charge batteries. I assume because there's no current limiting so the 12V battery would just eat current until the converter let the magic smoke out. If there's an easy way to limit current I wouldn't mind using that.

I did not see anywhere in the listing that it can not be used to charge batteries, I assume they mean it can not be used as a charger.
your 12v battery will taper down the amps when is charged and not consume energy from the dc/dc if not needed. so this should be perfectly fine.

And the battery will sulphate and die early...because it is not a battery charger.

remy_martian said:

And the battery will sulphate and die early...because it is not a battery charger.

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Would you mind expanding on this a bit? Electrically speaking I'm not sure I understand the difference between a DC-DC converter and a battery charger

A DC to DC supplies 12.0V to satisfy your car accessories and will kill your lead acid battery over time.

A battery charger keeps the lead acid battery and the car accessories happy.

The term "DC to DC" is used in the context of EV OEM components, but it is NOT the same as your Alibaba DC to DC converter....they are battery chargers.

xevion said:

Would you mind expanding on this a bit? Electrically speaking I'm not sure I understand the difference between a DC-DC converter and a battery charger

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Lead-Acid battery charger has multiple stages in the charge cycle with different voltages to maximize the life of the battery. A solar charge controller will have the same capability.

well, all 12v batteries from all electric cars charge with the DC/DC converter. is basically an alternator, and most ICE cars, don't regulate the alternator charge to the battery, just like a dc/dc, so while you are right about the stages on a lead acid charger, that does not explain how all other cars do it.
I have build several ev conversions and worked on Tesla's, even installed tesla's DC/DC converters on my EV conversions, and non of them do anything about regulating the charge to the 12v. never had a problem.
I also think it is an overkill to do anything about it. but if it makes you feel better, then you could install a solar charge controller, but then the dc to dc can only be feeding the solar charge controller, and all accessories will run directly from the battery that is being charged by the solar controller and the dc/dc.

Alternators typically put out some 14 volts, which corresponds to "bulk" stage of the lead-acid charging.

Teslas go through 12V batteries like $hit through a goose -- bad example of how it's done.

My GMC goes dead regularly. One run of a few dozen miles on the alternator and the battery is rejuvinated for weeks.

Whether the accessories run off the charger or the battery is a matter of bean counting. Put a black box around it and it all runs off the HV battery.

remy_martian said:

Teslas go through 12V batteries like $hit through a goose -- bad example of how it's done.

My GMC goes dead regularly. One run of a few dozen miles on the alternator and the battery is rejuvinated for weeks.

Whether the accessories run off the charger or the battery is a matter of bean counting. Put a black box around it and it all runs off the HV battery.

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Teslas batteries do only last 2 years, so yea, pretty shitty, but are you really gonna go thru all that trouble so that the battery can last an extra year? if you are lucky !?
I think you are right in everything you said, but my point here is that is not worth going thru all that trouble for another year on the battery.

remy_martian said:

What trouble?

Box A

Box B

Pick the one that cares for the battery up front is my point, and it's not Tesla, and it's not a xV-12V dc-dc off Alibaba.

Yes, you'll power 12V stuff, but a battery is ~$120, which is 4000 miles' worth of electricity 😛

My car batteries last 5-7 years. The Bolt EV 12V battery is a champ at 3 years old right now. The GMC regularly discharges below 8V (lack of use and vampire power...I run the truck once every month or two) and is on its 3rd year, also - but its battery was procured used.

The last battery in the frickin' Model X lasted a bit over a year.

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So, how do you propose he connects everything, and what are the parts he needs to buy in order to get this done? could you post some links on products and how to connect them properly?