WattCycle 12V 300Ah Mini inside look

[robbob2112]

Once my new BMS gets here I will have fresh wire handy, but intended to re-use the existing wire and just cut it down -

The positive is 4 x 8awg and the negative is 3 x 6awg

Black wire from BMS to terminal is 13" long
Black wire from BMS to B- is 11" long'
Positive red wire is 11.5" long

very similar cross-sectional area, but the smaller wires with the higher resistance per foot would mean the positive terminal would get a tiny amount hotter than the negative... at least that is what I think initially....

And I am wrong - the negative post will generate more heat than the positive post - @WorldwideDave - this might be your problem in the Chins -- they use the 4 x 8awg reds to try and balance the 3 x 6awg negatives + BMS.... but no matter how you slice it - the negative post will get hotter than the positive unless they get the cable lengths/resistance inside the battery just right.

See the second picture - that is a screw impression where it was between the case lid and a B- screw on the BMS.

It doesn't take much imagination to believe in a RV that could rub through the silicone and be a dead short between the right most B- screw in the BMS picture and the positive output wire ... You still watching this thread @Will Prowse ?

From the IR calculation on the battery that means we really would have 8000amps through the 7.5" or red + 11" of black to the cell. One wire of red and 1 wires of black.

So,

B+ --- 7.5" 6 awg red --- 11" 8 awg black --- B-


Used the artificial idiot to calculate when the wire reaches 200c and when it vaporizes given it is in a confined space. Took into account the cross-sectional area of the wire, length of wire, resistance of wire, Ir of battery, voltage of battery, confined space starting at 25c


Short answer - 0.054 sec to reach 200c

Wire vaporizes in 3.87 sec -- and at this point the wire is 2562c -- gas generated from vaporization of the copper is 156L- so the top will pop off shooting metal and hot gasses everywhere.... then things will cool off depending on if it caused a fire and if it didn't cause a cell vent.


So, with a pinched wire in an RV setup where the battery is strapped down so it had downward force applied to the top cover if a wire happens to be on top of a screw like mine was..... at some point the battery will do a max dump of current... and I suspect it will cause a fire.


Worst case, the cells the wire is laying on have their thin cases melted and they short/vent -- this results in 560L of gas.... 112L of which is hydrogen - which means we have a boom factor...

 

[robbob2112]

Evidence to support my theory

The positive is 4 x 8awg and the negative is 3 x 6awg

Black wire from BMS to terminal is 13" long
Black wire from BMS to B- is 11" long'
Positive red wire is 11.5" long


0.25MΩ for just the positive cable
1.10mΩ for the B- through the BMS to the P-

more resistance for the same current means more heat generated.

In theory they need to keep the negative wires as short as practical to keep the waste watts as low as possible. My 24" of wires is completely unnecessary. Looks like they increased the wire AWG size to drop the resistance a bit, but maybe they should have gone to 4awg X 3 to get it lower...








At 280amps - wasted power at the terminals from inside the battery

Positive - 19.6W
Negative 86.2W


In 5 minutes - open air - 4/0 wire x 2ft long attached -- accounting for convective cooling


And it steadies out at
Positive terminal 146c
negative terminal 443c

insane and to small a wire apparently

at 100amps
Positive 61c
Negative 123c

Calculation shows the best would be 2 x 2awg wires... or 3 x 4awg wires... --

for 2 x 2awg the negative temp is 72c - for 100amps
for 2 x 2awg the negative temp is 147c - for 200amps
for 2 x 2awg the negative temp is 258x - for 280amps


Non-linear curve because P = I^2 * R ... .


So this must play into the battery design as well...

Larger wire, larger terminal .. balancing act

and the solution is to operate at the least current possible to waste the least heat possible.


So,

conclusion - keep the positive and negative wires as short and as large as possible.
Making the wires larger is better than making them shorter since the resistance per foot decreases non-linear by cross-sectional area where it is a linear relationship for for length ---

A temp difference between positive and negative is expected and negative will be hotter... and can be ignored.

 

[dude47]

I created a new thread for those interested in the Dumfume (stupid?) batteries. I cracked mine open today and it was interesting to say the least. @Vigo you will want to take a look.

D

Thread 'DUMFUME 300AH Happy Surprise'

Jan 28, 2025

I purchased 4 of these on temu. Looking at the dimensions , specs and physical appearance I believed they were likely a relabel of the Wattcycle brand batteries 300mini (280ah). I figured the manufacture was likely trying to offload some of them under some under another name. With temu's super coupons (if you have ordered from them they have this really cheesy deal where if you make purchases they give you coupons to make more purchases) the cost I paid for all 4 was $850 OTD with two purchases with $150 off $500 coupons.

They arrived today and I couldn't help myself, after I got the kids...

• dude47
• Replies: 271
• Forum: Vendor Review Corner

• 
• 
• 

 

[BrunoTPM]

Help! I'm a newbie to all of this and trying to parse and understand the real world ramifications and risks of the potential design / manufacturing defect(s) on this 280AH Wattcycle battery having installed it in my Class C motorhome. Have travelled about 100 miles with it installed and am using it while dry camping near Santa Barbara, CA. Am trying to get a sense of whether the potential catastrophic failure of this battery is 1,000,000 to 1 odds, or if I should be calling Hazmat to pick up and dispose of this Chinese Bomb before it goes off (FYI - "Chinese Bomb" is a commonly used term in the RV world for substandard off-brand Chinese Trailer tires that tend to prematurely fail catastrophically, but I digress). Am leaving in a couple days and would like to understand the risk to my family and house on wheels before departing and what course of action, or inaction to take. TIA

 

[robbob2112]

In my opinion -

See the pictures above -if the top is bulged up like the one with the level on top then I regard that as dangerous and a possible fire waiting to happen.. the reason I say that is the red cable I had that was riding on top of the screw...

Second photo in post 24

Post in thread 'WattCycle 12V 300Ah Mini inside look'

Jan 18, 2025

Received my two 12V 300ah mini's with similar issues.
One battery had the lid popped off and the other seemed fine at first.
After further inspection during my install I noticed that the top had a large bulge in it. I believe due to the BMS contacting the lid.
This is obviously the reason for the lids piping off in shipping.
And will most likely have the same problem when they are bouncing down the road in my motorhome.
I agreed with customer service to reattach the lid of the first one. but after doing that it is obvious that that battery has the same issue.
Contacted Wattcycle again with...

• F29DCB

• 

Second photo in post 76

Post in thread 'WattCycle 12V 300Ah Mini inside look'

Jan 28, 2025

Once my new BMS gets here I will have fresh wire handy, but intended to re-use the existing wire and just cut it down -

The positive is 4 x 8awg and the negative is 3 x 6awg

Black wire from BMS to terminal is 13" long
Black wire from BMS to B- is 11" long'
Positive red wire is 11.5" long

very similar cross-sectional area, but the smaller wires with the higher resistance per foot would mean the positive terminal would get a tiny amount hotter than the negative... at least that is what I think initially....

And I am wrong - the negative post will generate more heat than the...

• robbob2112

• 
• 

If the case top is flat then there is little danger (cables next to the bms, very low risk of issues.)

If the case top is slightly bulged then it is a toss up. (Cables over the bms, some small risk of issues.)

If it is either of the second two and the battery has a MRBF or class T fuse attached as close to the terminal or on the terminal then there is no more risk than any other battery of lfp chemistry.

That is my assessment based on what I see.

 

[BrunoTPM]

In my opinion -

See the pictures above -if the top is bulged up like the one with the level on top then I regard that as dangerous and a possible fire waiting to happen.. the reason I say that is the red cable I had that was riding on top of the screw...

Second photo in post 24

Post in thread 'WattCycle 12V 300Ah Mini inside look'

Jan 18, 2025

Received my two 12V 300ah mini's with similar issues.
One battery had the lid popped off and the other seemed fine at first.
After further inspection during my install I noticed that the top had a large bulge in it. I believe due to the BMS contacting the lid.
This is obviously the reason for the lids piping off in shipping.
And will most likely have the same problem when they are bouncing down the road in my motorhome.
I agreed with customer service to reattach the lid of the first one. but after doing that it is obvious that that battery has the same issue.
Contacted Wattcycle again with...

• F29DCB

• 

Second photo in post 76

Post in thread 'WattCycle 12V 300Ah Mini inside look'

Jan 28, 2025

Once my new BMS gets here I will have fresh wire handy, but intended to re-use the existing wire and just cut it down -

The positive is 4 x 8awg and the negative is 3 x 6awg

Black wire from BMS to terminal is 13" long
Black wire from BMS to B- is 11" long'
Positive red wire is 11.5" long

very similar cross-sectional area, but the smaller wires with the higher resistance per foot would mean the positive terminal would get a tiny amount hotter than the negative... at least that is what I think initially....

And I am wrong - the negative post will generate more heat than the...

• robbob2112

• 
• 

If the case top is flat then there is little danger (cables next to the bms, very low risk of issues.)

If the case top is slightly bulged then it is a toss up. (Cables over the bms, some small risk of issues.)

If it is either of the second two and the battery has a MRBF or class T fuse attached as close to the terminal or on the terminal then there is no more risk than any other battery of lfp chemistry.

That is my assessment based on what I see.

1) This battery is from the more recent shipment / lot around mid-January.
2) The case top looks to me to be moderately bulged as best as I can measure with tools available at the campground.
- Measured lengthwise and holding one end of the straight edge down flat against the battery top on one end,
the other end of the straight edge is 3/16 - 1/4 inch higher. (Less than second photo in post 24, more than flat).
3) Second Photo on post 76 requires opening up the battery, not something that I or most folks are going to do.
4) The battery was properly installed with an MRBF fuse on the positive terminal

Thank you to robbob2112 for providing an answer / clarification that a novice can understand.

From re-reading the posts on this thread, it doesn't seem to me that Wattcycle has any clue as to their potential liability regarding this issue if someone's RV goes up in flames or explodes due to these defect(s). If people are in it when it happens, they could be looking at criminal negligence (or worse) and jail time in addition to civil suits given that they have been apprised of these defects. IMHO - The only rational move for them at this juncture would be to recall all of these batteries before something catastrophic does occur.

 

[robbob2112]

The real issue with that is it is very difficult or impossible to sue the Chinese companies... they just fold up, go bankrupt, and throw a pan against the wall for a new company name.

 

[RV8R]

Thank You @robbob2112 & also @F29DCB

We have to draw our own conclusions, but in regards to this WattCycle Mini 300 (280), I will not be buying them. If also places a question mark with WattCycle in general for me. If they are offering the deals they have for customers to keep their products & also responded without considering the possible risks ,,, well “Flash in the Van” comes to mind.

If they are willing to show their safety features & disprove @robbob2112 posted theory / scenarios that would be helpful ,,, Don’t worry & we will offer you a deal to keep your 300 mini, doesn’t cut it for me.

 

[robbob2112]

So, looking more in the wattcycle bate and switch thread - the circles on the top lid appear to be injection molding leftovers from the mold.

I think you can fix all the issues by popping the top, putting some thread around the wires and pulling them down alongside the BMS, then closing the lid... The big bulge is wires over the bms terminal, the medium bulge is wires over the bms board, and the flat ones are wires alongside the BMS....

No, their quality control sucks...

DumFume's 300ah is better designed with a different BMS and the wire routing is superior. But mine were 280ah cells just like the wattcycle fiasco - I would bet the same mfg using different parts... but still bargian basement batteries.

 

[RV8R]

So, looking more in the wattcycle bate and switch thread - the circles on the top lid appear to be injection molding leftovers from the mold.

I think you can fix all the issues by popping the top, putting some thread around the wires and pulling them down alongside the BMS, then closing the lid... The big bulge is wires over the bms terminal, the medium bulge is wires over the bms board, and the flat ones are wires alongside the BMS....

No, their quality control sucks...

DumFume's 300ah is better designed with a different BMS and the wire routing is superior. But mine were 280ah cells just like the wattcycle fiasco - I would bet the same mfg using different parts... but still bargian basement batteries.

Ya ,,, Warranty & Liability ,,, You Touch It - You Own It ,,, Warranty & Liability that is !!

Along the same lines as “Possession being 9/10”.

Appreciate The Report !!

 

[robbob2112]

You really think you are going to get warranty past a few months on tnese?

 

[RV8R]

You really think you are going to get warranty past a few months on tnese?

Not at all

But I would wonder what liabilities I might be picking up.

 

[OleDawgRV]

I wonder what they changed - Looking at your video again it seems like the lid is the same ... I am thinking maybe their fix was to just let the glue dry more - and once replaced the wires don't ever lay flat again ... either way I have scuff marks inside my lid and on the top of the cell directly under the terminal screws

They should just send a new battery to anyone that had the lid pop or refund - period - the 100ah battery they sent free would be fine if it was just a loose lid - but not with the other issues.

And everytime I move it, the lid pops back off

No mine was not bulging. Mine was a recent update without the lid issues

Will I have the same problem. I received 2 WattCycle 300s with the top off, as to the refund (2 100ah batteries). Can I connect those to the 300's in parallel with a Victron Multi-Plus 11 3000?

 

[robbob2112]

You have 2 x 300a with tops off and 2 x 100ah that were free?

The loose lids are fixable with a bit of string to pull the BMS wires down along size as you close it and ensure they are not laying across the BMS.

And yes, you can connect all 4 in parallel if you want - use bus bars - and use MRBF fuses on each battery positive terminal to match the BMS output. i.e. for the 100amp BMS is the 100ah battery use 125amp fuses. For the 200amp BMS inside the 300ah version use 250amp fuses ... but here is the thing - you need to use the wire to support 250amps on all batteries.

If there is a fault in one of the 100amp batteries it would receive 500amps of power for a split second until the fuse on it blew - so it could overheat/melt the insulation on a smaller wire sized for 100amps. If you want to add a safety factor fuse at the bus bars as well.

 

[OleDawgRV]

You have 2 x 300a with tops off and 2 x 100ah that were free?

The loose lids are fixable with a bit of string to pull the BMS wires down along size as you close it and ensure they are not laying across the BMS.

And yes, you can connect all 4 in parallel if you want - use bus bars - and use MRBF fuses on each battery positive terminal to match the BMS output. i.e. for the 100amp BMS is the 100ah battery use 125amp fuses. For the 200amp BMS inside the 300ah version use 250amp fuses ... but here is the thing - you need to use the wire to support 250amps on all batteries.

If there is a fault in one of the 100amp batteries it would receive 500amps of power for a split second until the fuse on it blew - so it could overheat/melt the insulation on a smaller wire sized for 100amps. If you want to add a safety factor fuse at the bus bars as well.

Thanks,
I guess my question is, with my Victron Lynx set up, shunt and distributors, how should I structure my battery bank? In parallel with the 2 300s being 1&2 and the 2 100s being 3&4, using bus bars and MRBF fuses, how would you construct this bank? From the shunt, what is the best layout for these batteries?

 

[robbob2112]

Not very neat but - MRBF on each battery post - connect up to the lynx all in parallel ... The MRBF is a fuse and a fuse block - I get them from pkys or mouser --- there are fakes on amazon so I don't trust them unless they are blue sea.... The pkys and mouser are 1/2 the cost of the blue sea and made by the same vendor - just relabeled