Deep discharge battery suppliers?

[Rob Morley]

That would make a nice little Arduino project. :-)

[tabbypurr]

I'd use a comparator or opamp

NT

[newshound]

Agreed, ELV is easier (I used to run 12 volts from a workshop to my parking bay for trickle charging, only switched on when required. But someone else mentioned SWA.

[Rob Morley]

But would yours have flashing lights and stuff?

[Theo]

I'd spend £ 2.19:

or, if you're feeling flush:

Theo

[T i m]

Our 3 certainly did and I've used it to good effect more than one occasion. ;-)

Not the sort of thing I was going to ask Mum to try though and was interested to see if it would start on the battery when I got there.

Cheers, T i m

[T i m]

That looks interesting. Any idea if there are any instructions that cover the two pots Theo?

That was the one I was referring to in my first post (but couldn't find it with my quick search).

There is a bit of 'slugging' on the voltage threshold setting so when I was trying to calibrate it using a bench PSU you had to leave it quite a while between adjustments to make sure it wasn't going to trip early / late.

The other thing I'm thinking of doing is powering the relay (or the voltage sense input) from a separate supply, rather than the generic input connections. That's because if you have a reasonable load even though the heaviest cables you can fit into those connectors you still get some voltage drop variance, if you are running different loads (as I was when doing battery capacity discharge tests).

Alternatively, you could use the onboard relay to drive larger external relay(s) and so 'offload' most of the load current completely.

It also has reasonable hysteresis so it shouldn't cut back in again once the discharge current voltage depression relaxes again.

Cheers, T i m

[tabbypurr]

non-flashing leds. You could spend the extra tuppence and fit flashing ones if you really want.

NT

[Theo]

No idea, but I think I saw LM358 on a picture somewhere. That suggests it is just a comparator circuit and you can work out what it does from the layout. I'd ignore the rather complicated schematic about charging they show, and just understand that it has a power supply port, a comparator input port, and a set of relay contacts. It wouldn't take very long to experiment with what the comparator inputs and pots do.

Not to stop anyone doing a project of course, but buying one of these and repurposing it is cheaper than buying the bits.

It also depends how you want to handle the load of the relay. On my digital widget (VAC-1030A) the 30A relay takes just under 100mA, so energy consumption is about 1W continuous. You could do something with bistable relays, but would need to ensure there's enough energy available for the final disconnect.

Theo

[T i m]

Voltage thresholds and (therefore) any hysteresis maybe?

I had. ;-)

So that layout is what I was suggesting re the LVD I mentioned, the load and sense paths managed separately?

It depends if they are raw or 'damped' like the one I was playing with. It made it quite difficult to accurately bench-set the trigger threshold (even ignoring the voltage variation because of different loads on the measure and the battery etc). Nothing stopping one pulling the cap they probably use for that whilst calibrating it though?

Quite! I would often rather tweak something that already exists (or even assembling a kit) than to start from scratch.

Whilst not much when say discharging a battery at 5A, it might if discharging a smaller battery or over a longer time.

If you wanted to ensure the final load (inc the HD relays, if powered by the load and included in the calculations etc) was constant then you could power two, having one in both the output states (you could use two single pole c/o relays as a two pole switch or switch the +ve of a battery between charge or discharge paths)?

Cheers, T i m