Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[bbdave]

I am building a sub and considering battery options i have seen on other subs contacts for charging on the outside of WTCs why do these not short? also do Nimhs need to vent to charge or can they be sealed?

Dave

[Snowwolflair]

 A lot of subs have lead acid batteries - gell type - in the water outside the model. If its fresh water the loss is minimal, but you have to clean the terminals every so often. Not so good in chlorinated water as you get chlorine gas being liberated.
 It also has the advantage that no switches are required if everything powers up in the correct order.
 
 
 

[malcolmfrary]

If its fresh water the loss is minimal, but you have to clean the terminals every so often.

Of course, you have to know exactly how fresh the fresh water is.  Any mineral content, be it from dissolved limestone if its that kind of area, acid rain if it isn't, agricultural runoff or a lot of wildlife in the area, will turn the water into electrolyte.  The cleaning is likely to be often rather than occasional, and I would consider a waterproof cover of some description for when its in water.  Duct tape rules.
Any battery should only vent when the charging is outside limits, and is doom to any sealed battery, since that which is vented is something that is needed on the inside, and cannot be replaced.  The venting is just a safety feature to stop the thing exploding due to excess internal pressure, and intended to extend your life rather than that of the battery.

[Snowwolflair]

I would consider a waterproof cover of some description for when its in water. 

Vaseline

[malcolmfrary]

Even better for underwater, the same with added silicone.  Works in undergound cables.

[bbdave]

Well if it's fine to seal them in a tube then problem solved 

Dave

[NFMike]

Venting is not the only issue with sealing batteries up in a container. When in use - being charged or discharged - they will get warm and if the heat can't escape they will get hot. That can lead to failure or worse.

Provided you aren't pushing them by using high rates of charge or discharge (eg. prolonged use of high power or using a fast charger) they'll probably be OK if not tightly enclosed and insulated. But if they will be worked hard you should consider some means to remove heat from them - for example maybe sealed in an aluminium tube (heat conductive) rather than a thick plastic one.

[Subculture]

It's usual to seal off the positive lead with a gland. Have a look at OTW and Sheerline installs for inspiration. They both run batteries in the drink, and have positive terminal seals.