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Question about NetDIMM and its battery

PascalP

PascalP

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So my NetDimm is blank after a power cycle and I want to replace the battery.
Anyone know which battery type to get?

And how long would a fully charged battery hold a game in the memory?
 
http://wiki.arcadeotaku.com/w/Sega_Naomi_DIMM_board_and_GD-ROM#DIMM_board_Battery

If you put in high capacity batteries, it will last easily 5 days or more. I salvaged the small PCB from the original battery pack. I don't think you can leave it out as it's part of the charging circuit. It looks like this:

P1130050.JPG
 

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the model number batteries and how to hook them up are in the AO wiki: http://wiki.arcadeotaku.com/w/Sega_Naomi_DIMM_board_and_GD-ROM

there are a shit-ton of different model 18650 batteries.
http://lygte-info.dk/review/batteries2012/Common18650comparator.php

There seem to be some 5200mAh models out there, I'd suspect those would last more than a week in such a low draw situation.

I've been meaning to do this myself but haven't got around to it... it'd be great if someone posted up a battery replacement guide :)

EDIT: a quick search on Amazon reveals some 6800mAh models! now I'm wondering if anyone makes a cheap battery holder for these...
 
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twistedsymphony said:
the model number batteries and how to hook them up are in the AO wiki: http://wiki.arcadeotaku.com/w/Sega_Naomi_DIMM_board_and_GD-ROM

there are a shit-ton of different model 18650 batteries.
http://lygte-info.dk/review/batteries2012/Common18650comparator.php

There seem to be some 5200mAh models out there, I'd suspect those would last more than a week in such a low draw situation.

I've been meaning to do this myself but haven't got around to it... it'd be great if someone posted up a battery replacement guide :)

EDIT: a quick search on Amazon reveals some 6800mAh models! now I'm wondering if anyone makes a cheap battery holder for these...
Click to expand...
I'll check out some 18650 batteries at my local electronics store.
As for the holder would something like this do?

http://batteryholders.com/part.php?pn=BK-18650-PC4&original=Li-ion 18650&override=Li-ion 18650
 
Those 9900mAH batteries are a scam. I remember seeing a video on youtube of someone testing them, and he hardly got 800mAH out of them. Worthless sh*t.
Battery holders do exist. I think miniinthebox is having some cheap ones for 2 16850 batteries on their site.
Getting the batteries themself for cheap is another story. You find the most ridicilus prices for them on fleabay. A problem with those devices is the fact they can't ship them with airmail as they are considered dangerous goods. If you choose Samsung, Panasonic or Sanyo, the quality should be fine. Avoid all other chinese makes as there is no guarantee at all about their capacity. The same cells are used in bicicle batteries, and even tesla cars use those cells in their batteries.
The netdimm batteries have 3 wires. The middle blue wire is connected to a thermistor that measures the batterie temperature. It probably shuts down charging if the batterie becomes 2 hot. Those pcb's should prevent the lithium cells against deep discharging as such can damage the cells. It should also shut off the charging voltage if the cell voltage reaches 4.2V Another thing some of them do is balance the charging to ensure that both cells are equally charged. If you buy something like a tablet battery, it should have such a pcb buildin.
I wonder if a 7.4V tablet battery could serve as replacement. You would only need to recycle the thermistor somehow.
 
PascalP said:
As for the holder would something like this do?

batteryholders.com/part.php?pn…0&override=Li-ion%2018650
Click to expand...
no idea? is it wired in the correct configuration as listed on AO?

looking at the datasheet it looks like it's designed to be PCB mounted, which is not what we'd want on a NetDIMM


PascalP said:
How about this?;
ebay.fr/itm/2-PILES-ACCU-RECHA…%3D12%26sd%3D252813142281

9900mAh
Click to expand...
I wouldn't trust batteries on eBay personally.
 
I also checked on Conrad (big electronics store in Europe), and their product range for 18650 is up to about 3500mAh for Samsung/Panasonic/Sanyo stuff.

They also offer a similar battery holder as linked before, these holders have just 2 wires, but I think could easily be adapted to the 3 wire setup.
This would make life a lot easier if the battery ever needd to be swapped out again.
+ I don't want to solder wires to a battery directly, haven't found 18650 with solder legs yet, but will search a bit further
 
Solder doesn't hold well on batteries. Usually they use spot welding to connect metal strips to batteries. A battery holder would be an easier way to use 18650 cells, as indeed, most come without wires or other ways of easy connection. The thermistor in the original battery pack measures approx. 10K at room temperature. It's an NTC. After half an hour in the fridge, it measured 15K.

http://www.ebay.co.uk/itm/7-4v-3000...er-Bank-PAD-TV-box-PDA-38110114-/172420818145

http://www.ebay.co.uk/itm/7-4-V-284...y-For-DVD-iPod-Tablet-PC-407080-/181627191811

This are 2 cheapo's that might be good alternatives. Not sure if they would fit easily in a netdimm. The bigger one of them is having a third (probably) thermistor wire, but it might be different. In such case, you could use the original battery pack thermistor. Those batteries have their own buildin protection electronics. If we could find the proper ntc, they could also be used in cases where the original battery and it's protection electronics are gone.

The real capacity might be less than advertised. That's a risk with all batteries on flebay.
 
cracked open my netdimm today to install some more RAM and check out the battery, but no joy...
There was no battery there, now I know why it doesn't hold the game even after a power cycle...

Idea was to open up the original battery pack and replace the cells with new 18650's, but as I have no original pack that idea goes down the drain.
Will check out if I can build something with 2 18650 cell and a NTC, but as I have loads of other stuff to do this will go on low priority for a bit now ;)
 
The original battery pack is having a small pcb that does the battery managment.
Only 2 18650 cells and an NTC can't replace that board.
You better choose one of the ebay battery packs I mentionned above, as those will have their own buildin battery managment board. (Only the ntc is missing on one of the batteries, and the NTC value could be incorrect for the other)
Without a battery managment board, you have no protection against deep discharge of the battery cells, so they can be damaged. The NTC is an additional protection, like a fuse, but basically the pcb should regulate the charging and discharging.
You can find such battery managment pcb's on ebay as well. They only cost a couple of bucks. I am just unsure how important it is for such pcb to be matched to the battery cells. Minimum cell discharge voltage and maximum charge voltage likely are equal for most type of lithium cells.

Be carefull with lithium cells. If they start to burn, it's spectacular. You can find movies of such on youtube.

It's not me selling those batteries on ebay. I just found them searching for a cheap 18650 replacement alternative as the prices for such are way to high.
 
PascalP said:
cracked open my netdimm today to install some more RAM and check out the battery, but no joy...
There was no battery there, now I know why it doesn't hold the game even after a power cycle...

Idea was to open up the original battery pack and replace the cells with new 18650's, but as I have no original pack that idea goes down the drain.
Will check out if I can build something with 2 18650 cell and a NTC, but as I have loads of other stuff to do this will go on low priority for a bit now ;)
Click to expand...
Sorry, got the netdimm without the battery pack :(
Out of like 9 netdimms I have bought over the last year or so, I think only 2 came with battery packs.
 
http://www.benl.ebay.be/itm/2-cell-...hash=item2361c5cd16:m:mzO_3ZXdWUET127NkX4591A

http://www.benl.ebay.be/itm/221942750719?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT

http://www.benl.ebay.be/itm/THERMIS...429733?hash=item51ae77ad65:g:Ld4AAOxy5jxSa773

If you really like to use 18650 cells, you could use the 3 items above I found on ebay. The only thing I haven't checked is the size of the BMS pcb. The netdimm output's 10.1V without battery pack connected. When I connect the original battery pack, it lowers to 8.2V It might become a bit higher if my battery pack is charged a bit more. It's at 8.04V at the moment.

The lithium cells in the ebay auction have solder lips. I don't know if you can solder on them, but if you do, you might not need a battery holder.
 
thanks, checked the parts out, those PCB's look quite convenient, so I will go ahead and order some this weekend.

How to connect 2 batteries in series to B+ and B- and the middle point to the BC connection makes sense.
P+ and P- to the Netdimm as well, but how would I connect the middle (T - blue) from the Netdimm and the NTC to the PCB?
T via the NTC to P+ or P-?
 
The NTC is simply connected between negative and the middle (T - BLUE) pin of the 3 pin connector.
So, you just have it's resistor value between black (negative) and blue (T)
 
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