Project: AUV

Hi,

I'm now just over a year into construction of a AUV/ R/C Sub hybrid. I've been working on the electronics for a while now, and have started to hit some brick walls. I've figured it was probably best to start a thread that post here and there.

Current progress can be seen on my site: **broken link removed** I'm hoping to have the hull,propulsion, ballast system and essential electronics woking by end of April time.

The problem I'm faced with at the moment:
The main batteries are 6 6V 162Ah sealed deep cycle lead acid all wired in series to give me the 36V I need for the main drive motor. I'd like to be able to monitor the voltage across each battery however I've no idea how to go about this.

I was thinking a 'heavy duty' (high voltage?) opamp using as a diff amp with wires coming from the postive and negative terminals of each battery.....Am I on the right track here or is there something I'm missing?

The problem I have is that it's not reletive to zero volts.....

Can any one help me please?

I started elec. lessons sept last year, but we've spent far too long (for my liking ) on logic gates/systems....

Cheers,

Michael

You could use differential inputs to measure across individual batteries, but if they are in series, and presumably charged in series, do you really need individual readings?.

I'll take them out for charging and so each one will be charged separately. It's just while they're onboard that I'd like to monitor each battery.

Michael

I would suggest it would be FAR better charging them all in series as they are used.

But then how would I ensure that every battery is fully charged?

Michael

Himszy said:

But then how would I ensure that every battery is fully charged?

Click to expand...

They will all charge and discharge together - bear in mind each battery is already three cells in series, you don't split the cells apart and charge them seperately!.

But these batteries have been on standby for a year or so and I'd like to look after them as much as possible.

BTW it's four isn't it? 4 x 1.5V = 6V?

Michael

Himszy said:

But these batteries have been on standby for a year or so and I'd like to look after them as much as possible.

Click to expand...

Charge them all up seperately initially (because you've no idea of the state of charge of the individual batteries), then put them in series and leave them like that.

BTW it's four isn't it? 4 x 1.5V = 6V?

Click to expand...

Oh dear! - no wonder you aren't very confident about them, lead acid cells are 2V!

Oops, anyway, if I do charge them up in one lot I guess it'll save on buying lots of chargers

Michael

You said sealed lead acid packs? Is there any access to the internals? If you find a cell imbalance it can likely be corrected by adjusting the sulfuric in the individual cells. If they don't charge equally then something is obviously going on with the internals, especially if all the cells were bought new at approximately the same time. This is only likely to occur after a long period of time, or abuse.
The reason I ask is because we have a 24volt fork lift at work that has 12 lead acid cells (2 volt single cells not sealed) we have to check the water levels every month and the sulfuric concentration needs to be tested every 6 months or so because it's a very abused power source. As the the primary operator I can be using both main hydraulic functions, plus full steering assist and have the accelerator on the floor all at the same time.

Himszy,

I love the way you got the buildings to look life like.

Mike.
**broken link removed**

Sceadwian,

I can't honestly say. I'm picking them up in two weeks (postage on 180kg of batteries is quite alot I hear ) and when I have them I'll let you know.

Michael