Charging SLA 12v /55Ah Battery from the Alternator

[rgallant]

Exactly as the says title Charging SLA 12v /55Ah Battery from the Alternator.

My electrical needs are very small , but I spend a lot of time in the spring and fall out about. Solar is not really a good option in SW British Columbia, during those times.

Use is for a couple of Led lights and running a Chinese Diesel Heater for a couple of hours in the evening / morning maybe 3 to 4 hours total draw of about 5-10 Ah from park to start.

I consider the 10 on the high side for my needs but you never know

Have done a ton of searching, but I keep coming up with overly complicated or expensive solutions, or just non applicable solutions

I can run an AC charger off a 45 watt inverter which will work fine for top up charging.

What I am looking for is a nice clean system that will support a larger battery if required without having to upgrade, without spending 200.00 or 300.00

If someone can direct me to a post that would give me decent ideas or provide some suggestions

 

[Buddha.]

This is in a vehicle not a travel trailer?
I would just run it as a second isolated battery.

How to make a cheap isolated dual-battery setup for $50

So there are a lot of kits you can buy to have truly isolated dual-battery setups. Those are VERY NICE kits. They are also very expensive. I try and replicate those kits without spending as much money, while still having a similar level of quality and/or reliability. There are constantly...

expeditionportal.com

You can mount your second battery under the hood if you have room or wherever it fits.

 

[DaveInDenver]

It's an SLA as in gel?

If you want to spend a lot of money this is a DC-DC gel cell capable charger:

OptiMATE DC to DC 12v 2 Amp Lead Acid & Lithium LiFePO4 Charger Maintainer

This item does not plug into AC Power. Item is powered by 12 VDC battery or 12 VDC Power-Supply.

www.batterystuff.com

Another option is that since a gel battery needs a lower voltage than your regular flooded all you need is an adjustable buck converter.

 

[rgallant]

Thanks @Buddha. and @DaveInDenver I forgot to add in the battery specs, it is basically the type of battery used in UPS, battery powered backup lighting systems, I will need to make sure I control the amps, for that battery about 15 is max that part I have sorted out although as I understand it charging amps from an alternator are around 5.

The Battery itself will reside under the hood, until needed then get disconnected, I have a shut off and simple method to manage that part.

But having seen batteries explode, I figure asking simple questions is always a good idea.

12V 55Ah SLA battery is engineered with Absorbent Glass Mat (AGM) technology offering superior performance and high reliability. AGM batteries are valve-regulated and spill-proof, allowing safe operation in any position

And I generally I am only stationary for a day mostly I roam, unless the fishing is good.

 

[DaveInDenver]

If it's really an AGM and definitely not gel then just parallel it like @Buddha. says.

It'll charge like any other typical automotive battery (which is to say as good or bad as you're currently doing with your starting battery). The current the batteries each want will self regulate, no need to over think it. Just make sure the two batteries disconnect whenever the engine isn't running.

If you're really worried about conditioning then the OptiMATE DC-DC is I believe about the only option other than the typical (more expensive) DC-DC chargers you see like Redarc, Victron or Renology.

 

[86scotty]

Seems like you just need a simple battery isolator, $50-75. Done.

 

[rgallant]

Thanks for help I think I have this sorted out

A VSR isolator to deal with the charging and protecting the main
A 150 Amp breaker to protect the main
And the disconnects and I should be good

I have a old UPS battery I can use as test battery for the setup

 

[86scotty]

Nailed it. I'm a big fan of the trusty old Blue Sea 7610 personally. I've installed 10 or more of em. Never had one fail or not perform flawlessly.

 

[llamalander]

I've had a 7610 fail, just got sent a new one to replace it. Bolted a breaker just below the relay and a short cable to the positive from there.
Pretty easy setup, I'm happy to have a new one. Worth noting, its for 120A max alternator, if yours is bigger, get a larger size, even if the draw is far less.

 

[86scotty]

I've had a 7610 fail, just got sent a new one to replace it. Bolted a breaker just below the relay and a short cable to the positive from there.
Pretty easy setup, I'm happy to have a new one. Worth noting, its for 120A max alternator, if yours is bigger, get a larger size, even if the draw is far less.

Not to get us off topic, hopefully it would help the OP. How did your 7610 fail? I've never heard of one failing but of course a few of anything can die, especially electronics.

 

[llamalander]

--OT--
not exactly sure... Had it mounted on top of the engine bay fuse box for a few years & I was chasing down some electrical issues. I realized that the main CPU was right next to it and had heard some folks talk about serious RFI on their HAM's when they had thick cables on that side of the bay. I pulled the 7610 & remounted it right next to the battery and rerouted the 2/0 cable in connects my batteries with. Rewired, it wouldn't connect at any voltage, either direction, after 10 minutes. Everything is potted, so there's nothing to look at inside.
One call to tec support and I took the voltages from the various points during the conversation. They put in an order for a new one, though it took a while to make. New one is in, works great with either the alternator on one end or the solar on the other--wherever there is charge the batteries link and fill up.
Electrical issue seems to be solved too, so I don't think a malfunctioning alternator killed it. Connections were tight and my grounds are oversized, apart from moving 16" closer to the battery, the new mounting is vertical and the last was on its back...
Cause of failure seems less important with a warrantee they were so ready to honor. They also saved me a bunch of money on jumper cables as I only need an 8" loop to jump myself. Having solar let me prop up a clapped-out starter battery for a good long time.

Back on topic, whatever relay you use, the larger the cables, the less voltage drop, which could be important depending on how your second battery needs to charge properly. Also, with two power sources, the linking cable should be fused (or have a breaker) at both ends. If the cable is damaged & shorts, both batteries need to be shut off.