Charging Leisure Batteries in Parallel

[uksparks]

Hi,

This is a question for anyone who can help with DC etc and Leisure Batteries.

I have a 500w load at 12v, made up of.

75w car stereo which includes 15w per Chanel, and 425w of LED lights.

I have 5x 100Ah Leisure Batteries all connected in Parallel, total of approx 500Ah.

My load is 500w at 12v which is approx 42A.

I am going to be running the load on the batteries every night for approx. 5 hours, so draining the batteries by 200A.

My question is, how long does it take to charge a set of batteries from flat, and also fast charge them?

My problem is, I need to be able to maintain the battery level so that I can have this 500w load used for 5 hours every night for 30 days, I need to charge them every night.

Any thoughts on what the best way to do this is?

At the minute this doesn't quite exist, well it does, but its 20 years old and using inverters and mains powered stereo and lights with 3 batteries.

 

[uksparks]

I did wonder, would it be better to have some form of disconnect for each battery and then charge each one independently?

 

[Richard Burns]

The amount you are using the batteries at 200Ah per night is going to be straining the capability of the batteries, especially if you calculate in any losses.
If all batteries respond exactly the same you are probably taking them to 50% charge which should just be OK, however if there is an imbalance then some batteries may be drained below 20% where you may get problems.
Make sure all your connections are secure and low resistance as resistance losses can be considerable and affect the discharge.
Try it once and check the level of charge in each battery.

To charge the batteries fully may well take longer than the 19 hours available, but it is going to be close. Fast charging them will reduce the efficiency of the batteries and you do not have much leeway for this to happen.
Use a good quality charger designed for those batteries.

 

[uksparks]

Thanks Richard, I'm just sitting here drawing a layout so that I can use a change over switch so that it kills all the + links between the batteries and switches it I we to the battery charger, but one for each battery, my only problem now is cutting the negative between the batteries at the point the charges are on so need to find a suitable contactor.

part of the problem I have is the tow vehicle for this float does not and will not fit an auxiliary output as I could use that to keep the batteries topped up.

i reckon if I actually charge each battery on its own it should work ok, I can only assume if I had say 4x 100Ah batteries in parallel and pull 200A in a day, it would hopefully only pull 50A from each roughly? Does it work like that?

 

[davesparks]

Float? As in carnival float? Put a generator on it

 

[davesparks]

Why do you want to break the -ve link whilst charging?

 

[amlu]

possible to do but you will need a beefy charger... standard one can do like 5-10A, that is for one battery, if you have more batteries the charger will struggle a lot or shut itself off.
invest in couple more chargers, charge batteries separate. or get a small suitcase generator and connect its 12v parallell to the load and battery bank.

 

[uksparks]

It's the official Santa sleigh thing for the town, it's 20 years old and needs an overhaul.

i can't put a generator on it, they need it to just run on battery power unfortunately.

i thought that I would need to break the -ve between them as if you had for batteries all on charge independently, but left all the neutrals connected, would it not cause a problem?

i just felt like it would be better to break the links.

 

[uksparks]

This is it, it's going to look 100% better when made over.

 

[amlu]

equip the reindeers/towing vehicle with a 12v output?

 

[uksparks]

The tow vehicle is not wanting to do that, plus it's got to be capable of running on its own without the car.

 

[UKMeterman]

Ok,
Split the load into several different load groups, you do not want to have batteries in parrell, this causes the following issues;
1. The fault currents will be HUGE.
2. Some batteries will come to end of charge first and start to gas whilst others still need charging.
3. Makes it awkward to charge the batteries.

Have one battery the master and it power the coil in standard 12V relays to turn the various loads on the other batteries on and off. Don't forget to have appropriate master fuses and sub fuses in the circuits, a 12V battery will MELT anything that shorts it out.

425W of LED, that is very bright, can you arrange for alternating pairs of LED chains on the same battery so the average power is reduced?

Look up car fuseable links for the main fuse for each battery or a BS88 in a small holder, then use CAR FUSE HOLDER | Premier Farnell CPC UK to break it up into sensible lumps.

Note that a 50amp DC relay you were asking for is not an easy thing to do (contact arcs) and be careful of the sequence of the charger so there isn't sparking through hydrogen gas...

Are your batteries non spillable and are they properly secured?

 

[SJD]

425W of LED, that is very bright, can you arrange for alternating pairs of LED chains on the same battery so the average power is reduced?

I agree, this is like having a few kW of conventional halogen lighting, if this is just for some fancy lights on and around the float. Or are you powering a few floodlights as well?

 

[davesparks]

Note that a 50amp DC relay you were asking for is not an easy thing to do (contact arcs) and be careful of the sequence of the charger so there isn't sparking through hydrogen gas...

Isn't it? I've got 3x 200A relays in the landrover for the various functions of the system controlling the two batteries.

And winch relays are pretty common for 12V and 24V at pretty high currents

 

[Lucien Nunes]

OK, so you are sharing your 42x5= 210Ah of discharge (note, Ah = amp-hours, not A = amps, for capacity) between 5 batteries, so 42Ah each. Or 42% depth of discharge over 5 hours, equating to complete discharge over 12 hours. This is faster than the 20-hour rate lead acids are usually rated for (except tractions, for which the capacity is usually given at 5-hour rate) so their effective capacity will be less than 100Ah. But not catastrophically so, perhaps we could say it's a 50-60% depth of discharge each day which a leisure battery will stand. So the discharge side of things is reasonable.

Charging - there is no way to 'fast-charge' a lead-acid, as there is for a Li-ion or a NiMh. The chemistry limits the maximum rate of charge as full-charge is approached, otherwise it will gas heavily and be damaged. With an intelligent 3-stage charger, that goes through bulk, equalise and float stages, you can recharge a flat lead-acid to 100% in 12-16 hours, if it is correctly sized, and yours won't be flat, so this is also do-able. Of course, near the end the charge rate will be low, so the initial charge rate will need to be more than 42Ah*efficiency/available charge time. A suitable charger for the whole bank might be 30-40A output, as this will be able to supply much of the needed charge in the first half of the cycle, ready for the rate to fall off.

40A regulated intelligent chargers are expensive, so you might choose to split the battery bank into individual batteries for charging. Five 8A chargers won't break the bank and will work, provided that all batteries are charged equally ready to be paralleled up again. Charger outputs are usually floating so you only need to break one pole of the circuit between the batts.
Ensure any switching is very low resistance to avoid differing rates of discharge, and fusing as mentioned above.

Relays are no problem here, as the maximum currents are not very high (you're not running starter motors etc). However, if you parallel up two batteries of very different states of charge, there will be circulating currents and the load won't be shared equally, so the relays should all be fully rated for the maximum currents involved or perhaps 100A, not just a fraction of the load.