Chainsaw's Simple 12V DIY Backup System

Ronmaggi

Curse you autocorrect! Serial. I think my iPad is suggesting that I am a crusty granola eater...

Ronmaggi

Restisting... The... Urge... Mustn't go to the time black hole... Damnyouautocorresct.com...

tom77

mattyoga wrote:

If the batteries are identical and aged the same you can charge them in parallel, though if they have different characteristics one will take more of the charge than the other.

Also if one develops a faulty cell it will 'steal' charge from the other healthy battery when running on backup.

Are you pulling an average of 3.5Amps eg 42Watts on backup (based on max battery depth of discharge of 50%)? Thats a fair draw, is that just for an air pump?

How long do you want your backup system to run for? If you want to extend range much more you'll need to factor in the likelihood of cloudy days.

Well I have had this battery for almost 12 months now although it hasn't been used much (since it's a backup system) and always kept topped up. I can get the exact same battery size and brand/type.

I used an online calculator.. not sure what depth of discharge it was considering… The air pump is 35W I think.. I will double check that though since perhaps it was 25w.

I would like it to run 2-3 days.. I give a bit of a range there as I know the amount of sunshine will vary the time… perhaps it is just as cheap to have 400w of solar with one 120ah battery rather than 200w solar with two 120ah batteries.

tom77

Ronmaggi wrote:

People regularly parallel batteries on boats to get more amp hour capacity. By paralleling we mean connecting the positive terminals together and the negative terminals together, as opposed to cereal when the positive from one battery connects to the negative to another, doubling the voltage. Like Mattyoga said, you need to use batteries of the same type, size, and age, or you are asking for trouble. People often think that they can just slap another battery in parallel whenever their budget allows them to purchase one, but the older batteries will rapidly degrade the new battery to their level of degradation. It goes without saying that you can not mix AGM, gel cell, and standard flooded batteries. Their charge windows are rather different, and you will likely destroy the more expensive limited electrolyte batteries.

Just two weeks ago I got an expensive lesson on wrong battery for wrong job. I swapped my 40ah lead acid battery (14kg) for a lithium battery (1.3 kg with less ah but more cranking power)… however apparently small 2 stroke outboards do not regulate the voltage from the motor to the battery very well.. and when running full throttle a lot of volts go to the battery up to 17-20… suffice to say lithium batteries don't like being overcharged.. so I ended up leaving a smoking/melting battery on a sandbar in fear of it exploding on me :cry:

waste of $230… although I had checked with a distributor if it was alright to use with out boards and he said it was… after all they are used in 2 stroke motorcycles and jet skis… guess he was wrong

Gunagulla

If it was LiFePO4 chemistry, it's a very good idea not to take them over 3.9V/cell, as bad things can happen, as you discovered!
17-20V is well into the danger zone. I run my house off-grid from a Lithium battery and keep it below 29V (24V system, equivalent to <14.5V for a 12V system).
You could run Lithium on the boat, so long as you had a reliable regulator installed... 17-20V is bad news for Lead-acid batteries too!

tom77

Yep that's why I asked the distributor if it was ok.. since on their website they said you didn't need any kind of BMS.. Lead acid get damaged too, but they are apparently better at absorbing the extra power.. and in my little speed boat it is rare to run it continuously for more than 30-45mins.. of course the bigger the lead acid battery the more it can absorb…

tom77

Is there a cheap option for regulating the voltage from my motor to the battery? something small and simple that I just wire the +/- to?

is this the something I could use
http://www.ebay.com.au/itm/Regulator-Re ... 800&_uhb=1

Gunagulla

Hard to say as the specs are a bit light on. It says it is a rectifier and regulator, so it must be designed for AC input, but if you didn't need one before when you had a Lead-acid battery, you must have DC, in which case you don't need a rectifier.
I couldn't really recommend a regulator without knowing what you are feeding into it.

tom77

I see what you mean… I was reading about what they were for and they seemed to mention (in the case of motorcycles) the size of the motor in CC.. I guess because that effects the power output.
My outboard is 30HP which I think is 440cc or there abouts.. I was reading the service manual and under alternator it says it is a 12v 80w and that the 'charging performance at 5500rpm (wide open throttle) is 5A

Gunagulla

That's capable of over 1kW, so not sure how a 200W regulator would go... the magic smoke may escape! It is hard to imagine they would put an unregulated alternator on the motor, but perhaps you could just use a regular car alternator regulator? The old mechanical ones as used on Holdens in the 60s and 70s were extremely reliable. Car wreckers no doubt still have them for $nottoomuch

What capacity is the Lithium battery? Is it only used for starting?

Alternatively, would a small PV solar panel, say 30W - 50W with a regulator, be enough?

tom77

The battery 'was' a SSB 12V 360CCA LFP20CH, I was mainly using it for starting but also for powering my trim tilt unit and 2 bilge pumps… neither of which draw much power. I was almost considering just not hooking up the outboard to the battery now as I also have a chord for pull starting it and it is easy to do.. but I just like to be cool and turn a key

Not enough space for a solar panel (even a 30w one).. boat is only 2.6 metres long.. I just have it on a float mode on the charger when it is in the garage.

Perhaps I can find an old car regulator like you mentioned or perhaps just keep the lead acid as it is… it has lasted so far and the motor has probably done 40 or so hours with it connected to it before I tried the lithium. :think:

It was a very scenic battery fire.. no fireworks.. luckily :lol:

Gunagulla

I guess you are better off finding out what happens when you overcharge Lithium on a small boat than in a plane- a bit less panic involved!

I'm considering using LiFePO4 for a backup system on my AP, with a DC air pump and 300W sine wave inverter I already have, to power a water pump. The big LiFePO4 system (off-grid house) has been 100% reliable so far, but doesn't protect against, for example, forgetting to turn the power point on after turning it off to work on the pump. I just need to accumulate some cash for the battery.

tom77

yeah they are getting pretty good.. there was however a bit of panic as on a boat as small as mine the fuel tank is never raf enough from the battery

although in defines of the battery it never exploded or had flames come out.. just smoke.. but it was hot enough to melt/burn some buoyancy foam that surrounded it.. but it would have destroyed the boat like some of the older lithiums may have.

I like looking at some of these battery packs and dreaming of going off grid

https://www.ev-power.com.au/-EV-Powerpa ... ries-.html

I use a timer to turn off my pumps when I need to work on them as I have also forgotten them sometimes… although it can be another point of failure… but I use 2 timers.. one for air pumps and one for water pumps at least both would fail

(hopefully)

Ronmaggi

I think Mastervolt might have a solution. They make DC-DC converters that stabilize the heck out of voltage. ProMariner makes zero loss battery isolators that regulate too. The nice thing about that is one alternator output goes to two batteries, while keeping them isolated from each other. Automatic Charge Relays will connect two batteries when there is a charge current, but the newer zero loss battery isolators keep them discrete. They are soooo much better than trying to remember what setting to put your old 3 way battery switch on. Considerably better than getting in a fight with your wife about what setting she was supposed to put it on.

tom77

Sounds good Ron.. are those regulating isolaters expensive though? just looked online and some seemed pretty fancy… I would have thought there was rather low tech solution.. some of the images showed cooling fans.. seems almost like a computer, but perhaps I was looking at the wrong thing

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Chainsaw's Simple 12V DIY Backup System

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