Reply With QuoteHey Brett,
Can I ask why two cranking batteries?
Cheers Nomad
Andy thanks for entering the conversation.
I am leaning towards the DC-DC set up at this stage due to looking after the deep cycle batteries and giving them the best shot at lasting for a while. The 240 volt onboard charger will be connected whenever the boat is trailered up in the shed so I am hoping this will keep the batteries happy. I am not sure what the current solar panel is good for and being 18 years old is probably on the side of retirement. Once I get everything set up I can then address this if required.
As for the 2 x cranks they should get all they need from the alternator one would think. Like yourself, looked at the lithium batteries and although the price is dropping on these certainly need to drop a lot more before I will think about it. Yes I am glad only dealing with one engine and that's a inboard which I think is a little easier.
Trying to keep the battery set up simple but also correct is a challenge. Out on the water for 2-3 nights I really want something I don't need to worry about. I can see solar becoming important to achieve this as you have mentioned.
Hey Brett,
Can I ask why two cranking batteries?
Cheers Nomad
The minimum CCA for the engine is 700 which you can get with no problem in a single crank battery and much higher.One's I have looked at with a high CCA are rather physically large and I have limited room in the area the battery will be mounted. When they say minimum you can guarantee you will be better off much higher. Diesels are high compression and can give your battery a work out. I can fit two small batteries in this area so that is the only reason.Originally Posted by NomadNoosa
FWIW Brett, the Deka Intimidator start batteries I use are only 273L x 175W x 212H. 770 CCA.
DC-DC is defiantly the better way to go, its just comes down to cost at the end of the day. Flooded lead acid batteries are cheap, DC-DC not so much! In my case I figured that the small amount of time I run the engines (typically from Shorncliffe to Moreton or Peel) did not justify the cost of a DC-DC, and I my alternators are only good for about 12A each. The only real reason for the VSR's was just to get some extra juice on cloudy days.
IF you want the batteries to last a long time, the key is not to discharge to much, hence the reason a low voltage disconnect has been suggested. This is the main problem I have, especially on days where there is no full sun. I have an AGM as a house battery, they can cop a bit more punishment with discharge than a flooded lead acid, but a flooded lead acid will last longer if you look after it. Always pro's and cons to everything, you just need to figure out which boxes need more ticks!
BTW, regarding the solar panel age, as long as the power output is still close to what its rated for, no need to change it. I tested one (BP branded) for a friend last year that was nearly 30 years old, and it was still delivering almost all its rated current.
I had one of those BP branded ones which I just recently gave away to a mate and it was phenomenal, the sun would be setting and it would still be pumping hard, like chalk and cheese compared to a lot out there now. I think these were the ones used to charge roadside phones etc.
I bought some BP Solar batteries from the local solar pilot plant for $20 each they built years ago when it was demolished. They may have been 15 years old? found the original specs for those panels on the net, and they were all over 90% of original output rating. I parallel up 4 (80w ea) and get up to 21amps from the setup on bounce, more typically 18 amps on steady sunshine.
Dc-dc overrated. Good for voltage drop situations where you should have used bigger cable. Much made of multistage but its overrrated. Yr altenator and battery resistance means it transitions from bulk to float anyway.
Go bep vsr for $55 on line. Oh shxt moment jumper leads. Lead acid start and AGM bank is same chemistry. I bought a n70 800cca start for $154 yesterday from repco (33 percent off)
You have a 120amp aleternator. Depending on your loads and SOC you can be using a fair bit more than the 40amp max of the dc-dc charger. You want to make the most of that 120A. Far more important imho is a battery monitor. Go victron. Can set alarms for both house and start. Set the alarm for your house at say 12v. Try not to go below that. Will give you AH used, rate of disharge, rate of charge and every other spec you could need. Has contacts if you want to rig a relay
I should mention also theres no need for an expensive multi channel charger when using a VSR (or dc-dc charger) for that matter
Simply hook up your battery charger and the VSR will energise and switch in the other battery or bank (however you have wired) just as if you had the motor running.
Soin not having the Multi channel charger and the dc - dc charger you could save well over $1k.
If you want to hook up solar you can buy a charge controller of ebay for $17 delivered. Battery place has them in the shops here (same unit) for $199
myusername this is all interesting from what you have written. Sounds like the battery manufacturers and auto electricians are out to up sell us on equipment. Pity the engine didn't have a rope start and no battery required would even be better. Thanks for the insight.
Now I am really confused, my understanding was that AGM and Gel batteries required a higher charge initially to get it going, but from previous posts it is saying that AGM needs to treated with kid gloves. I haven't checked what my motor outputs and that is something I will do over the next few days. So is a 120 amp charge from the motor a better charge rate than using the dc/dc charger at 40 amps or are there other variables that us plebs don't know about.
Mate someone will explain it to us dumb bastards soon I hope.Everything I have been told has just gone down the toilet.
Sorry guys, but I am probably going to confuse you more by giving you more techie info here, but hopefully it helps to give a better understanding. Let me know if it doesn't!
An AGM can accept a higher charge current, but are fussy about voltage. IF you increase the charge voltage to about 14.4V, then the AGM will draw more current (if your charger can supply it) than if you charge it with 13.8V
3 things kill AGM's, over voltage, heat and letting the run dead flat. A flooded lead acid is also susceptible to the same issues, however they are a more forgiving. Provided the voltage is set correctly, you will get the fastest charge. A lower voltage will result in a lower charge current and hence a longer charge time. OF course a longer charge time is not desirable in a cyclic situation because you want the battery to charge as fast as it can
BTW, what outboard has a 120A alternator? If the alternator can supply a full 120A then depending on the AGM size you may actually need to go down the DC-DC route. You would need to refer to the AGM manufacturer, but the accepted rule of thumb for charging AGM's is about 20% of the rated capacity, ie for a 100Ah battery the charge current should be limited to 20A.
IF you check the data sheet for a Century 120Ah AGM you will see that the max recommended charge current is 36A, which is 30% of the rated capacity. There is also a charge algorithm that shows 13.7V for cyclic use (ie what you would do in your boat). In this case, the 40A DC-DC would be a perfect fit for the battery.
These are the recommended figures that will prevent the battery from overheating during charge and maximise the life of the battery. If your charger has a temp sensor that bolts to the battery terminal then you can usually charge with higher currents.
Look after the battery and you will get 10 or more years out of it. Treat it like shit (ie, as most start batteries are) you will get 2 years.
I think there’s really 2 issues that I think are confusing things for people.
1 - the engine charging system
2 - mixing battery types.
1 - as far as I’m aware most engines alternator systems be it automotive or marine or whatever are designed to suit the normal lead acid battery and they are really a “battery maintenance” function. They aren’t designed for long term charging of deep cycle type batteries.
2 - yes different batteries have different charging requirements, that a regular alternator charging system doesn’t cater for and aren’t designed for.
So will a VSR work - yes it will allow the regular charging system to do it job. Ie Good for regular lead acid starting batteries.
If you are using a deep cycle battery system to its full capacity and running appliances for whatever reason on your boat for eg - is a VSR going to give you the long term battery life and allow a full charge to a deep cycle battery, no.
I reckon if you are investing in specific batteries you’d be better off with a dc/dc charger suited to the task.
Saltwater fishing, boat mad but has a job that gets in the way.
Quick question for Andy - with regard the running of a fairly high wattage inverter to run the microwave. My own thoughts would be to only do it with the engine running - in which case the VSR would most likely be engaged and the load would be spread across the entire battery installation and the alternator ( Brett is running a diesel inboard hence the 120 amps). Obviously you could do this by bypassing the DC-DC when required as well or wouldn't you bother.
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