Boat battery egine starter

[Lef]

Hello i have 32 (4S/8P) of these batteries Just Wonder how to connect them so they be able to handle 400 amp pulse for start a boat engine

LiitoKala 3.2V 32700 6500mAh LiFePO4 Battery 35A Continuous Discharge Maximum 55A High power battery+DIY Nickel sheets
https://a.aliexpress.com/_rwQg5A

The batteries are these i have copper bars and nickel strips 0.15 x 0.2 and battery holders Just Wonderinh whats the Best way to connect them any advice helpful

 

[e-beach]

According to the specs, you need to connect at least 8 in series (8s) to get 400a. Not to mention some fancy tab welding and/or custom battery holders with thick plates to bolt on to. (something like a 6 gauge wire only flat.)

 

[fechter]

8 parallel will be borderline for a big engine starter but I've seen smaller packs used as car starters.

How big is the boat engine?

As far as connecting them, I would recommend getting them spot welded. A spot welder might cost about as much as the batteries though. Ideally find somebody close that has a battery spot welder and bribe them to weld your pack. Generally packs are welded with nickel sheet. Copper is a better conductor but nearly impossible to weld to a battery.

 

[Lef]

The engine atm have an acid battery i Just want to swap it to lifepo4 i Just wondering if the nickel strips only can handle 400 amps pulse for start the engine and what the Best way to connect them for safety i already have a spot welder Thank you already for reply, i dont know if someone have done anything similar Just want to get some ideas, also need to be 12v+- the pack

 

[e-beach]

Do a test. Use two small c clamps to connect a short length on nickle strip, like 2 inches long, between your existing battery post and the battery-post-clamp. Start the boat to see if the nickle melts. Then you will know.

 

[999zip999]

What motor ?

 

[fechter]

Here's a pack I built a while back. The nickel sheet joins the rows of cells. In a 8p pack, the nickel would only be carrying 1/8 of the total current at any point other than at the ends. On the ends, I used 8ga wire soldered to a strip of nickel. Soldered first, then spot welded to the pack. In an engine start application, the peak current would only be present for a few seconds so heating should not be an issue.

 

[Lef]

What motor ?

motor is
Mercury 50

 

[Stealth_Chopper]

What fun?
A marine engine can be vital for boaters who safety depend upon it.

(1) pull on the rope to startup that 'Fifty' anytime, 'non?
Good Luck

 

[methods]

I have started many engines with hobby packs.
I have a large set of heavy gauge, heavy duty Jumper Cables. Coming off of that I have 8pcs Anderson PP45's

You can start a 5.2L V8 from a single, 4Ah, tired old 20C pack....
Do it 2 or 3 times...
But I did it once and a single pouch in series lit off into a fireball

What you are concerned with is turning the motor over once the first weak cells in series drop below operating voltage. For this reason, I would use a "Lead Acid Approach" of grossly oversizing in capacity.

Doing so will give you tons more punch, will make it so that the cells are not being pushed, and will lower the likelyhood that you will experience flame-off or out-gassing.

In this particular use case (Extreme High Current for what could be 10 seconds)


I suggest focusing less on summing the C*Rate x Capacity (for rated current handling) and focusing more on the POWER TRANSFERRED and how long you can do that for.

Example
Discharge = 400A
Capacity = 6.5Ah
C-Rate = 35-55A per cell (back calculate it)
Capacity = ?

For 10 cells in parallel you would have 65Ah available (that is an ASS TON of lithium)

If you run 400A for 6 seconds. . . that is
400A for 1 hours is 400Ah
400A for 1 minute is 400Ah/60 = 6.7Ah
400A for 1 second is 112mAh

So turning over for about 6 seconds should equate to about 1% of your pack.
That is a damn-lot of margin. I would call that "dead nuts safe" to an order of magnitude.

Current per cell would be 40A. . . so for bursts like 10 seconds, that would be completely fine. Just dont turn it over for a minute and a half* (as that would bring cell heating into the equation, which you do not want to worry about)

-methods

 

[999zip999]

Wow !

 

[Lef]

what about this 200a bms

https://www.aliexpress.com/item/32901047855.html?spm=a2g0s.12269583.0.0.60e41a85YncogJ

 

[fechter]

what about this 200a bms

https://www.aliexpress.com/item/32901047855.html?spm=a2g0s.12269583.0.0.60e41a85YncogJ

That should work but hard to know if the specifications are accurate.

 

[vreppeto]

I would build the pack with nickel fuses for each cell. If a cell goes bad the fuse will burn and drop that cell from the pack. In addition to over building the pack this would make it pretty safe. Strip the insulation from a battery cable and solder it all along it's length to the nickel strip connecting the parallel packs to each other. One on the positive end and one on the negative. This wire should be equal or nearly so to the battery cables you are running from the battery to the starter. (The solder will increase the effective cross section of the copper cable.) Like "methods" said in a previous post, over build the pack. 4s8p is only 24 amp hours. 400 amps divided by 8 is 50 amps per cell. I would suggest at least double that. Thats only $240 for battery cells. That's about the same as you will pay for decent deep cycle AGM. The 50hp motor is less than 1000cc and it can run at 14.5:1 compression before it begins to get tired. It's not likely to pull more than 150 amps max. However these cheap cells tend to sag under load to about 2.8v. Anyway, 32 cells will probably work. :thumb:

 

[vreppeto]

A cheap 40 amp bluetooth bms could work. Run the output of the bms to the ignition switch and/or the main fuse terminal. Run the signal line from the ignition to the starter relay coil. Bypass the bms for the main battery cable and run it directly to the contact on the starter relay. This way the bms can still cut the power by controlling the signal to the starter relay if the voltage drops too low and the starter will not be subject to a 200a limit by the bms.

https://www.aliexpress.com/item/400...chweb0_0,searchweb201602_5,searchweb201603_53

 

[fechter]

A cheap 40 amp bluetooth bms could work. Run the output of the bms to the ignition switch and/or the main fuse terminal. Run the signal line from the ignition to the starter relay coil. Bypass the bms for the main battery cable and run it directly to the contact on the starter relay. This way the bms can still cut the power by controlling the signal to the starter relay if the voltage drops too low and the starter will not be subject to a 200a limit by the bms.

That would work but would be sort of a pain to wire up. On some cars it might be pretty easy where the main starter positive wire just goes to the solenoid and there is a separate smaller wire for everything else. On some cars that split is hard to get to. Not sure about a boat motor.

I've seen people use a single port BMS at the pack and start cars with it, so if the BMS can handle it, the wiring will be much simpler.
I also agree you may want a larger capacity battery as there may be other items (lights, radio, etc) that you may need to run off the pack with the engine off. If there are no other loads, then a small-ish pack might be OK.