New DPV - Dive Xtras

[tdmp]

For those of you with the tech tube upgrade, how are you weighting your Blacktip for saltwater?

I have an early model travel and just got the tech tube. The tech tube came with a weight plate inside the tube. Should I take out the 2 from the nose cone or leave them in, too? Do I need lead shot or add'l weight over that? I have a big bolt snap on the nose already.

BlackTip Scooter Weighting

 

[Miyaru]

Bringing back this issue:

you missed the part about them only being rated for 9.8A discharge. They will self destruct in your scooter which pulls more current than that. So that's a big no no
You need a cell with 5000mah capacity AND at least 20A discharge. Not exactly sure how much current the motor draws at max speed but its way over 10A.

you also need a spot welder and some willingness to risk burning down your garage if you really screw it up

The engine will draw 1 / 2.2 / 3.8 / 6.2 / 9.6 / 12.8 / 17 / 22.8 amps for the respective gears (see pdf).
A single cell (in a 5S1P pack) would require batteries that support those 22.8A.
Two cells parallel, would double the max current discharge.
Three cells parallel, eg. the Samsung 50E, would allow 3x 9.8A = 29.6A and that's above the power drawn in the highest gear.

Correct or did I make a mistake here?

 

[Whitrzac]

That is correct.

 

[broncobowsher]

I thought (and maybe stand to be corrected) that the flexvolt packs were 3 battery groups in a single pack. Depending on how the (DeWalt) tool is configured it could be in series (60V) or in parallel (20V). Since these run in the 20V mode wouldn't that allow greater current capacity than a single cell rating?

Add in the capacity for the smaller pack (5Ah) that I believe are two battery groups in a pack. So only 2/3s the amp load capacity of the flexvolt. Note that this will not be exact, I am sure there are different cell specifications between the different packs, but they should still be somewhat close.

 

[Miyaru]

A flexvolt pack has a mechanical switch that indeed changes the batteries from a parallel to serial alignment. An option that is not used by the Blacktip.

These are the cells used in the original packs:

Of course these packs were not designed with a DPV in mind, but to meet powertool requirements. So considering a maximum current draw of 22.8A, using 15 Samsung E50 batteries in a 5S3P configuration meets the Blacktip requirements. That's a 15Ah pack.
Empty battery housings are now available as well, so building your own packs is becoming interesting.

 

[macado]

A flexvolt pack has a mechanical switch that indeed changes the batteries from a parallel to serial alignment. An option that is not used by the Blacktip.

These are the cells used in the original packs:
View attachment 624500

Of course these packs were not designed with a DPV in mind, but to meet powertool requirements. So considering a maximum current draw of 22.8A, using 15 Samsung E50 batteries in a 5S3P configuration meets the Blacktip requirements. That's a 15Ah pack.
Empty battery housings are now available as well, so building your own packs is becoming interesting.

Hmm. Not a bad idea. Where are you seeing empty DeWalt packs that take 21700 cells? I see generic ones that take 18650 cells. Maybe I can keep an eye out on eBay for some defective packs that are selling cheap. I have access to a spot welder. I already own 2x 9Ah and 2x 12Ah packs but would be nice to squeeze a little more runtime/range out of this little budget scooter.

Making some very basic assumptions on published specs for 9ah/12ah batteries, a 15Ah pack should give around ~150 minutes runtime (~4.3 mile range) at cruising speed.

I suppose if one were so inclined they could also forgo the DeWalt form factor itself and make a larger lithium pack that also fits but it would require making a custom battery sled and some modifications. Sticking with the DCB format is probably best bet.

 

[Whitrzac]

You can tell the difference between the 18650 and 21700 dewalt packs just by looking at them. The 21700 packs are noticeably wider.

I poked dive xtras and they said the blacktip has a hard coded 28a current limiter.

A 10s3p pack with the 50e batteries would be 15ah and should provide enough current.
Or just go a 4p setup and run for a few days, haha
Samsung 50E 21700 5000mAh 9.8A Battery - INR21700-50E2

 

[stuartv]

I suppose if one were so inclined they could also forgo the DeWalt form factor itself and make a larger lithium pack that also fits but it would require making a custom battery sled and some modifications. Sticking with the DCB format is probably best bet.

If you start building a custom pack with extra cells, just remember that the Travel tube is basically neutral in fresh water with 2 x 12Ah packs and no additional weight added. So, if your custom pack weighs more than 2 x 12Ah packs, the scooter will end up negatively buoyant and nothing you can do about it.

 

[Whitrzac]

If you start building a custom pack with extra cells, just remember that the Travel tube is basically neutral in fresh water with 2 x 12Ah packs and no additional weight added. So, if your custom pack weighs more than 2 x 12Ah packs, the scooter will end up negatively buoyant and nothing you can do about it.

Hmm, I wonder if you could get it to trim with a custom pack.
Make 1 big round 10s3p pack at the front of the tube to counter the tail heavyness of it.

The travel is a lot easier to use when it trims out and negative than purely neutral.

 

[tdmp]

Hmm, I wonder if you could get it to trim with a custom pack.
Make 1 big round 10s3p pack at the front of the tube to counter the tail heavyness of it.

The travel is a lot easier to use when it trims out and negative than purely neutral.

Doing a little research, the current 2170 4000mAh cells are 66.8g and the 5000mAh cells are 69g. 15 cells per pack X 2.2 g = 33 grams per pack (0.07 lbs) or a total weight increase of 66g / .14lbs for both packs. A slight but manageable increase, whenever they come out.

Of course, once the new Telsa 4680 / 9000mAH cells come out, I think we'll see a gradual adoption of them in other applications just like the 18650 and 2170s. Just image the burn time in a 4680 cell PTB of the future.....