[Ant7K]

Hey

Anyone know if I can use a 12V 140amp Durite 0-727-33 voltage sensitive/intelligent Split Charge Relay to power/charge x2 batteries at the same time by connecting them both to the VSR?

I have a 110ah leisure bat and also a 30ah bat from a golf cart that I want to use to power my 12v TV and run the telly separate from the main leisure battery.

I tend to fall asleep with the telly on and don’t want to draw power from the main battery while I’m asleep so had the idea of using a smaller battery just for the tv.

My mind tells me this would work as I’m just splitting the output from the vsr ...but as the batteries are different sizes / aH would it cause anything weird to happen ‘electrically ‘ wise?
Charge/load balance issues?

If so...I’ll just install x2 vsr’s but if I can run them both of one vsr be great

Cheers
Ant T:

 

[Jungleist]

I think....its a bad idea...because;

The smaller battery will become charged before the larger one, and the volts from that battery will raise the average voltage seen by the charging circuit, and the larger battery won't charge properly.

Also, if the charging goes on too long because the voltage is being dragged down the other way by the larger battery, you'll overcharge the smaller one.

When not on charge, the smaller one will continue to discharge whilst the larger one has capacity, so any inverter (or anything else which senses voltage) will continue to run knackering the smaller one because the volts will drop down too low. Again, this is because the voltages average out across the two.

A matched battery set is the best way or separate chargers.

 

[Ant7K]

I think....its a bad idea...because;

The smaller battery will become charged before the larger one, and the volts from that battery will raise the average voltage seen by the charging circuit, and the larger battery won't charge properly.

Also, if the charging goes on too long because the voltage is being dragged down the other way by the larger battery, you'll overcharge the smaller one.

When not on charge, the smaller one will continue to discharge whilst the larger one has capacity, so any inverter (or anything else which senses voltage) will continue to run knackering the smaller one because the volts will drop down too low. Again, this is because the voltages average out across the two.

A matched battery set is the best way or separate chargers.

Thanks for that mate!
Would you use a separate VSR then or use a DC to DC charger?
I’m thinking of running two VSRs..one for each battery

 

[triffic]

The smaller battery will become charged before the larger one, and the volts from that battery will raise the average voltage seen by the charging circuit, and the larger battery won't charge properly.

I agree that it's not a good idea, but what you say isn't the reason why. All other things being equal, a small lead-acid battery will have exactly the same voltage profile as it charges as a bigger one. If you wire them in parallel, the smaller battery won't become charged before the larger one. In effect, more current will flow into the larger one than the smaller one - so overall they will charge together at the same (slower) rate.

However, the main reason for avoiding using very different sized batteries is that they will tend to age differently, and then the worse of the two (typically the smaller one) will drag down the performance of the other one.

A matched battery set is the best way

Agreed - matched in type of cell technology, age/length of service and size.

 

[Jungleist]

What I was getting at was that if the batteries aren't the same type/size they may have different internal resistances so will charge or discharge at a lower rate.

Anyhow, definitely not a good plan with mismatched batteries, but parallel charging is used in lots of industrial applications.

 

[safetygav]

most domestic TV's have an eco setting where they'll go into standby after 4 hours or so, might be worth seeing if it has that function? probably still draws a tiny amount but not as much as when it's on.

 

[Jungleist]

Thanks for that mate!
Would you use a separate VSR then or use a DC to DC charger?
I’m thinking of running two VSRs..one for each battery

I'm going down the battery to battery charger setup, because I think i'll get a better recharge than a split charger.

In all honesty, I'd investigate an alternative to the second smaller battery, as suggested below a telly with auto standby or a timer that shuts it off after a set period of time.

Out of curiosity, I looked at what a 12v telly would use, the example I found uses 13watts (1.08A at 12v).

Even if left playing all night (12 hours) you'd consume 12amps, so from a 110Ah battery you'd still have 108Ah left in an ideal world. You don't say what else you have connected so it's a bit hypothetical.