I am planning to get a DC heater and run it off a 60V battery pack I just built. It's a 12V 25,000 btu heater. See this link -
Maradyne H-803012 Phoenix 12V Universal Wall/Floor Mount 25,000 BTU Heater
Would the battery fry the internal electronics of this heater for good or it won't fry and will only draw what it needs from the battery pack?
Or do I need to run the negative wire through the 5V line of say an ebike controller instead of connecting directly to the battery's negative terminal?
I highly recommend you go to this website
and go thru their tutorials--they should help you learn what you need to not destroy things or start electrical fires, and better understand the things you're working with.
For now, some basic info to help you figure this out, along with consequences of doing it the ways you're talking about:
You have a 12v device you want to power....you need to use a 12v source to power it. Not all "12v" is the same--if it's automotive 12v, then that's actually 13.6-14.4V.
Running 60v thru the 5v line of anything is a great way to destroy that.
Running the 60v's ground thru the 5v line of a controller, to then power a very high current device, is probably going to start a fire.
How many amps does the heater take? The link doesn't say, so a quick google search for a conversion to a unit we can use, like watts,
says
| 25000 BTU/hr | 7326.77675 Watts
|
To get amps from W and V (the only data we have), is W / V = A
7327W / 12V = 610.583A We'll just call that 611A as a guesstimate to use for calculations. You would need to get hold of it's specs or manual to find out what *actual* current it takes, and what it's *actual* input voltage range is.
How many amps could the controller you want to run the ground thru handle? Most of them use a 7805 regulator, which by itself could probably handle a few hundred mA (thousandths of an amp), so less than 1A. I imagine the plastic and silicon of the 7805 would actually explode at 611A.
How many amps can your wiring handle? Most of the grounds are 24g, maybe 20g at the largest. I doubt they can handle more than an amp or few themselves, enclosed in their wiring bundles, before they heat up enough to melt insulation. 611A will probably melt the actual conductor in the wires, hopefully before the insulation catches fire.
How many amps can your battery supply?
Since no info about the battery was given, then for some math to see what is required, let's say it's made from brand new P42 "molicel" cells, which are pretty good at high current.
Assuming you run them at their max 45A current (which will shorten their life and make them hot and have a lot of voltage sag), then to supply 611A would need 611 / 45 = 13.58, or 14 (since you can only use whole numbers for this), parallel cells in each group. Since it's a 12v device, and these are 4.2v cells, you can probalby only use 3s, if it's tolerant of voltages up to 16.8v then you can use 4s.
Let's assume it's not, so 3s 14p *minimum* battery size with those cells. Since that is 14p of cells that each have 4.2Ah capacity, that's 4.2 x 14 = 58.8Ah--you probably can't actully get the full capacity at that current rate, so let's generously round down to 50Ah, and to find out hte run time it's the 50Ah capacity divided by the 611A load, which is 50 / 611 = 0.08hours, or less than 5 minutes of runtime.
If you need to run this for several hours at a time (typical usage for heaters), let's say it's intermittent usage at 50% duty cycle over 12 hours, that's 6 hours of actual runtime required. It would need 6 x 60minutes = 360 minutes of runtime. If 14p is less than 5 minutes of runtime, then to get 360 you need 360 / 4.8 = 75 times the amount of capacity you have now. So you would need, for 6 hours of continuous runtime, 75 x 50Ah, or 3750Ah. for these cells, that's 75 x 14, or 1050 cells in parallel...times three of those in series, or 3150 cells total.
That makes it about half the size of a common Tesla car battery....
That's assuming also that hte heater will still run down near the 9v or so the cells will be at when near empty. If it's a simple filiament heater with no electronics, it will, just not as hot. If it's got electronics, then you have to check the specifications for it's shutoff voltage. It might be higher and that will mean you have less usable capacity so you have to increase the size of the battery pack to compensate.
This also assumes all your interconnects between cells, and your wiring, and interconnect welds/etc to the cells, can all handle the necessary currents.
What kind of protection does the battery have? Can that protection handle the heater current? If it has a typical BMS, it would need to be large and expensive to handle 611A, usually a contactor BMS.
If there is no protection to stop overdischarge, etc., then the battery itself could become a catastrophic type of heater, igniting and burning the pack, heater, room/etc., and contents. Not usually desirable.
