DC-DC Charger vrs VSR set up

[brett62]

Ok Andy. The set up I was looking (and still) at has temperature senor and the engine alternator produces120 amp's at 3000 rpm. The alternator will be connected to the crank bank and the DC-DC charger will be connected to the house bank. The DC-DC charger will be only charging the house bank and the solar will also be connected to the DC-DC charger. From what I have been told the alternator of that output will keep the crank bank charged and also have plenty left over for the DC-DC charger to service the house bank. Now a lot depends on how long the engine is running and how much power is being used and I also have a monitor to keep track of all of this. Also a low voltage alarm/shut off if all goes to shit will be installed. Will install a switch to connect both battery banks if I have a crank battery failure to get me started. The only draw on the crank will be the anchor winch and 2 x engine blowers which only run while the engine is operating.

The house bank will feed everything else in the boat and I will have 3 x Blue Sea's fuse boards and one fuse board will have what I would call the must have to operate like radio, nav lights, bilge pumps etc. This board will have a switch over so it can be run from either the house or crank bank.

I am starting fresh with the re-wire and have the perfect opportunity now to set it up while everything is removed from the boat. The wiring before was just a disaster waiting to happen even more so with a petrol inboard that was installed. The previous owner said he was not getting much life out of the batteries and had to replace them often. I didn't care to much about that for when I looked at the wiring it was all going in the wheelie bin anyway. I really don't know how it never blew up.

Anyway really want to get this right and everyone's input is appreciated.

[TheRealAndy]

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.

You guys got me at a good time. Stuck in transit at Singapore for 5 hours, but at least I have lounge access!

I decided to do the sums on a microwave first. I picked the cheapest JB model, which is a panasonic 800W unit. The specified power usage is 1250W / 5.6A at 240V. I will go with the highest figure, which is 5.6A at 240V.

Have to fess up here, not sure how much start up current a microwave draws. I know Victron products fairly well, so I will use the specs from one of their inverters. The have a 1200 or a 1600 VA model, and factoring on some inrush current I would run with the 1600VA model. At 12V, they claim 92% efficiency which in my experience is fairly accurate.

So doing the sums, for a small 800W microwave, you are going to be drawing around 120A @ 12V. Thats a lot of current to be sucking from a battery, even with the engine running. A small battery would run this, for example for a fully charged 120Ah battery in an ideal world you could get an hour run time out of the battery. In reality you can expect a hell of a lot less. I guess there is a chance you would overload the alternator but I dont have any experience in that area.

ME personally, I would not bother with the microwave unless you had shore power or a generator running or a very large battery bank (ie, 100's of Ah's). For boating (or even any rec activities) a gas stove is whilst not as quick is fairly efficient!

[myusernam]

AN AGM is a lead acid battery with glass seperators between the plate. Brett is repowering his cruiscraft with a steyer diesel which will have a normal bosh 120a altenator.
Altenator output voltage is with AGM charging specs (as they are a robust deep cycle lead acid battery)
I seem to recall at the beginning of the thread 200amp bank. I have a similar boat and and I went 2 x 160 AH - nice form factor. (long and skinny) good bang for buck. bout $400 each.
Check out the battery life comparison charts between cycling to 50% vs 30% discharge. - twice the life
max charge current is approx 30% of amp hours. I'd expect to see around 60 amps when the batteries are low with the above setup. To err on the side of caution and longevity I would go a bit larger than 200AH and you shouldn't exceed the max charge current..
You might be charging your batteries at 50 or 60 amps but also using 20 or more amps with the fridge or freezer running and all the other electrics on the boat.

Agm's are tougher and more forgiving than a normal battery.

[TheRealAndy]

Ok Andy. The set up I was looking (and still) at has temperature senor and the engine alternator produces120 amp's at 3000 rpm. The alternator will be connected to the crank bank and the DC-DC charger will be connected to the house bank. The DC-DC charger will be only charging the house bank and the solar will also be connected to the DC-DC charger. From what I have been told the alternator of that output will keep the crank bank charged and also have plenty left over for the DC-DC charger to service the house bank. Now a lot depends on how long the engine is running and how much power is being used and I also have a monitor to keep track of all of this. Also a low voltage alarm/shut off if all goes to shit will be installed. Will install a switch to connect both battery banks if I have a crank battery failure to get me started. The only draw on the crank will be the anchor winch and 2 x engine blowers which only run while the engine is operating.

The house bank will feed everything else in the boat and I will have 3 x Blue Sea's fuse boards and one fuse board will have what I would call the must have to operate like radio, nav lights, bilge pumps etc. This board will have a switch over so it can be run from either the house or crank bank.

I am starting fresh with the re-wire and have the perfect opportunity now to set it up while everything is removed from the boat. The wiring before was just a disaster waiting to happen even more so with a petrol inboard that was installed. The previous owner said he was not getting much life out of the batteries and had to replace them often. I didn't care to much about that for when I looked at the wiring it was all going in the wheelie bin anyway. I really don't know how it never blew up.

Anyway really want to get this right and everyone's input is appreciated.

So to me it sounds like the DC-DC option is the way to go, especially if you want the batteries to last. What size house battery bank are you running?


BTW, I am going to give a plug to the Blue Seas stuff. Discovered it last year when re-wiring the fixer-upper van I bought. The stuff is not cheap, but its pretty decent quality. They sell a circuit breaker block with plug in fuses which I highly recommend. IF you ever have to fault find problems at sea or on the road then fuses are the pits. Circuit breakers all the way if you can. You can even buy high powered waterproof ones for you main power feeds now, including ones large enough to run starter motors.

Whatever you do, dont use BEP switches. They are f#cking rubbish. I have them in my boat and I have a couple of spares because they are useless and break all the time. Replacing them is on the list of maintenance items. Just need to find a switch with terminal bolts on the front rather than the back.

Dont skimp on wire also. IF you need a bit, PM me as I have various Tycab stuff that is probably some of the best quality stuff and I will sell it per metre for what I pay. For what I dont have you can buy from <decided to delete this in case too many people start annoying them, PM for details> cheaper than you will pay anywhere else (this is where I buy it). They will sell some of the bigger stuff per metre, but the smaller stuff you need to buy in rolls.

[TheRealAndy]

You might be charging your batteries at 50 or 60 amps but also using 20 or more amps with the fridge or freezer running and all the other electrics on the boat.

This is a good point. When you battery gets close to a full state of charge, it will draw less current. If you have the ability to supply extra current, then some of that can power the accessories whilst the battery is getting the most it can.

Agm's are tougher and more forgiving than a normal battery.

This is not true. Dont believe everything you are told. AGM's are far less tolerant to abuse, especially when charging them. They excel in deep cycle applications because you can discharge them to a lower state of charge, and because they can accept a higher charging current.

The reason flooded lead acid batteries are still used in cars over other types is simply because they can stand a lot more abuse. Because they are abused, they are dont last, but an equivalent sized AGM in the same situation would be getting swapped out much more frequently.

[TheRealAndy]

I am checking out now folks. About to board my plane back home (yay). Will check back in when I get over the jet lag.

EDIT. I lied, just checked the tv screens and I still have another hour...

[scottar]

I am checking out now folks. About to board my plane back home (yay). Will check back in when I get over the jet lag.

EDIT. I lied, just checked the tv screens and I still have another hour...

If you're flying Tiger you could even have another day.......or week

[myusernam]

This is a good point. When you battery gets close to a full state of charge, it will draw less current. If you have the ability to supply extra current, then some of that can power the accessories whilst the battery is getting the most it can.



This is not true. Dont believe everything you are told. AGM's are far less tolerant to abuse, especially when charging them. They excel in deep cycle applications because you can discharge them to a lower state of charge, and because they can accept a higher charging current.

The reason flooded lead acid batteries are still used in cars over other types is simply because they can stand a lot more abuse. Because they are abused, they are dont last, but an equivalent sized AGM in the same situation would be getting swapped out much more frequently.

Dont want to get into a pissing contest but "dont believe all you are told" is a bit patronising. Disharging a battery deeply is abuse. don't do it at all. if you do it to a flooded wet cell it will be rooted. . An agm will recover with a shortened life. Car start batteries aren't really a good comparison. I don't know what else you are calling abuse but charging with an altenator is perfectly ok. There are many very large house banks on large vessels whose batteries are charged this way. I'm trying to contribute not start a dxck measuring contest.
Most literature contradicts what you are saying about this.
The worst thing is overcharging by a smart charger with too high a float voltage.

[brett62]

Andy the house bank will be 2 x 120 amp and I will be after wire for sure.

The Blue Sea's fuse boards I will be installing will have resettable fuses that lights up when they trip. The main fuses will be stationed at the stern and looking at breakers for these.

I am at present fiberglassing in the engine bay and stern area and sorting out what hardware will be installed so I can glass in the appropriate mounts and brackets. Not a lot of room at the stern so need to think and plan what goes where and also get access without having to pull half the boat apart for general maintenance.

As scottar has mentioned I will be running a 2000 watt inverter to run a microwave for heating up some meals for short time. Was wondering if I should have it connected to the crank or house batteries ?

[myusernam]

House bank.
What inverter are you using?
If you are getting a good inverter youd be crazy not to get an inverter charger. Only slightly more. I'd recommend the victron multiplus 1600/70.
Smart charging, (2 channel if u dont use vsr) seamless switchover between shore/inverter power. Set the foat voltage to the lowest setting.
And at 240amp housebank is fine to match with your 120a altenator. You wont exceed max charging current using a vsr. Of course charge voltage is also in spec. I can send you some tong test results of a similar setup ill be working on on the weekend if u like. Pair it up with the victron bmv so you can monitor your SOC and have an alarm or even a cutout so you never discharge below your set amount.

[TheRealAndy]

Dont want to get into a pissing contest but "dont believe all you are told" is a bit patronising. Disharging a battery deeply is abuse. don't do it at all. if you do it to a flooded wet cell it will be rooted. . An agm will recover with a shortened life. Car start batteries aren't really a good comparison. I don't know what else you are calling abuse but charging with an altenator is perfectly ok. There are many very large house banks on large vessels whose batteries are charged this way. I'm trying to contribute not start a dxck measuring contest.
Most literature contradicts what you are saying about this.
The worst thing is overcharging by a smart charger with too high a float voltage.

Clearly you have not read my posts, but hey, I'll hand over to you since you are the expert.

[ranmar850]

I think I'd be running the motor if I were using a high draw, such as when you are powering a 240v appliance through a 12/240 inverter ( think 20 x current draw of the 240v rating as a rough rule of thumb). And you would still likely be going backwards in charge as it would be beyond the alternator output of an outboard--the stern drive with the 120A alternator could obviously do better.
This is all very interesting, first time I've really had an interest in dc/dc charging. My useage for the new boat ( which i am currently doing 11 hours a day on the fitout of) will mostly be day tripping, hence a standard start/both/house with a vsr will be fine. But I will also be doing overnighters at times, with one particular trip likely going out to four nights. Bu the travel oven will only run while the motor is, and nights will be a small fridge and some LED lighting, so I don't think it will be an issue. I went for dual starting-type lead acid batteries, 660cca/825mca, instead of a deep cycle, and will change position on them every six months or so to even the useage.

[brett62]

House bank.
What inverter are you using?
If you are getting a good inverter youd be crazy not to get an inverter charger. Only slightly more. I'd recommend the victron multiplus 1600/70.
Smart charging, (2 channel if u dont use vsr) seamless switchover between shore/inverter power. Set the foat voltage to the lowest setting.
And at 240amp housebank is fine to match with your 120a altenator. You wont exceed max charging current using a vsr. Of course charge voltage is also in spec. I can send you some tong test results of a similar setup ill be working on on the weekend if u like. Pair it up with the victron bmv so you can monitor your SOC and have an alarm or even a cutout so you never discharge below your set amount.

myusername I am looking at the enerdrive 2000 watt inverter and had thought about the combined set up and yes I also have shore power so a plus also. Any information would be great as I am researching all opinions. Is this the one ? Would I then have a DC-DC charger set up with this ?


VICTRON MULTIPLUS COMPACT INVERTER/CHARGER 12/1600/70A CHARGING - 16A TRANSFER SWITCH

PRODUCT CODE : CMP121620000

$1,464.00

[myusernam]

sigh
i still dont iunderstand where we went wrong.
was it where i said agm's are tougher and more forgiving than a normal battery? I stand by that but perhaps i should have said traditional deep cycle battery. there's nothing contraversial about that. And AGM's are common under bonnet now with stop start technology

[Fed]

I'd go gas cooker & fridge, dump the solar and all the electronic charging wizardry.