DC output petrol / diesel generator

[Amy]

'You might have doubled the voltage & halved the amperage but the total energy stored IS THE SAME'

Only same if i have 24v lights and 24v everything else too. If i want to use any of that 24v in a 12v appliance, I double the ampage needed?

10 x 115ah batts = 1150 amps @12v
but half that for 24v (double the voltage, halve the ampage) and ive only got 575 at 12v.

The reason im converting back to 12v is because thats the most popular voltage for domestic appliances like LEDs, fans etc.

BUT, just thinking a step further, what if I did have 20 x 12v batts, wired them in paralel, would that give me 115ah of 240 volts and then I dont need an inverter?

[northern installer]

No that would give you 12 volts dc

[Amy]

Oh you smoooooth talker, you know exactly how to appeal to my better more rational side.

Ive always prefered quality over quantity and know it makes sense to do it once, do it right, so, ive put the kettle on.
WHat exactly are you suggesting?  Talk me through the system in simple talk please.

Amy,sit down,put the kettle on,and lets think this through...Q  why are you thinking of living aboard?  A  ...to get a more pleasant life,in better surroundings,at less ongoing cost and be able to relax and enjoy yourself with the simple everyday surroundings? OR: to spend every spare moment trying to find bits of old car to repair the unsuitable system that has let you down AGAIN ,wallowing in the bilges as you get black and oily removing yet another failed alternator,by the light from the paraffin lamp that has been the only source for the last 2 weeks,just wishing you could slip into a dry warm bed after a refreshing shower,but not a remote possibility until the electrics are fixed.............?
I think you should consider reworking your budget to cover installing a system that will work efficiently and trouble free with the minimum of maintenance for a substantial time,even if it means extending your fit out time to build up sufficient funds;perhaps saving money by purchasing good quality secondhand equipment,rather than trying to make life expired old car parts do a job they were not designed for when new.
Just being able to invite someone you wish to ...err impress aboard for dinner,without having to explain that the bog is out of action due to battery failure,must be worth the extra costs?  Sorry to go on about it,but I wouldnt want your dream to be tinged by niggling engineering problems that could be minimised by design,and possibly a budget reallocation

[johnrae]

Amy,
If you wire your 20 of 12 volt batteries in SERIES yo get not only 240volts DC - or 290 when fully charged but you also get a set-up that will be potentially lethal (excuse the pun) on a small boat.  Don't even consider that route.

You never took me up on the suggestion of buying a submarine !!  Plenty of amps there.

jack

[Justme]

'You might have doubled the voltage & halved the amperage but the total energy stored IS THE SAME'

Only same if i have 24v lights and 24v everything else too. If i want to use any of that 24v in a 12v appliance, I double the ampage needed?

10 x 115ah batts = 1150 amps @12v
but half that for 24v (double the voltage, halve the ampage) and ive only got 575 at 12v.

The reason im converting back to 12v is because thats the most popular voltage for domestic appliances like LEDs, fans etc.

BUT, just thinking a step further, what if I did have 20 x 12v batts, wired them in paralel, would that give me 115ah of 240 volts and then I dont need an inverter?

Amy I give up.

You are wanting to do a complex thing come here asking for advise yet will not listen to that advice.


Ok its your choice & your money but at least understand the mistakes you are making before you spend it.


What you have put above is just so wrong.

A battery stores X amount of power add all the bats up & you have Y the voltage & amperage DO NOT MATTER.

You start with 10x110ah wired to 12v you have 1100ah x 12v = 13.2kWh
10 x 110ah wired to 24v = 13.2kWh
If you convert that back to 12v via a dc dc adapter you will have SOME losses but not 50%.

Forget about amps & volts & work power out in watts & kw.

My advice is to go all 240vAC, you have more choice, cheaper, reliable, can be bought in a local shop, no issue with fixing it. Then for the ODD thing at 12v a dc dc adapter is not the end of the world.


The EXTRA cost saving of using 24v compared to 12v would pay for the stuff needed like DC dc converters.

Your 12v stuff will not work well if you skimp on cables as the V drop will be to large.

From your bat bank to inverter you are looking at 120mm2 csa cable if its more than a meter or so for a 3kw inverter. On 24v its half that (but prob use 75mm2 as its a standard size & will give less losses).

[Amy]

I know, I know, but i cant live soley on 240v, I have to make and store some for those quiet moments when I dont wish to hear the genny running or when I want the bathroom in the middle of the night.
This is where the problem is at. How to make and store it.
ok, I could make it as 240v but as ive already found out, a decent genny is beyond the budget. Im advised that the cheaper chinese ones arnt worth having as they die young.

'You might have doubled the voltage & halved the amperage but the total energy stored IS THE SAME'

Only same if i have 24v lights and 24v everything else too. If i want to use any of that 24v in a 12v appliance, I double the ampage needed?

10 x 115ah batts = 1150 amps @12v
but half that for 24v (double the voltage, halve the ampage) and ive only got 575 at 12v.

The reason im converting back to 12v is because thats the most popular voltage for domestic appliances like LEDs, fans etc.

BUT, just thinking a step further, what if I did have 20 x 12v batts, wired them in paralel, would that give me 115ah of 240 volts and then I dont need an inverter?

Amy I give up.

You are wanting to do a complex thing come here asking for advise yet will not listen to that advice.


Ok its your choice & your money but at least understand the mistakes you are making before you spend it.


What you have put above is just so wrong.

A battery stores X amount of power add all the bats up & you have Y the voltage & amperage DO NOT MATTER.

You start with 10x110ah wired to 12v you have 1100ah x 12v = 13.2kWh
10 x 110ah wired to 24v = 13.2kWh
If you convert that back to 12v via a dc dc adapter you will have SOME losses but not 50%.

Forget about amps & volts & work power out in watts & kw.

My advice is to go all 240vAC, you have more choice, cheaper, reliable, can be bought in a local shop, no issue with fixing it. Then for the ODD thing at 12v a dc dc adapter is not the end of the world.


The EXTRA cost saving of using 24v compared to 12v would pay for the stuff needed like DC dc converters.

Your 12v stuff will not work well if you skimp on cables as the V drop will be to large.

From your bat bank to inverter you are looking at 120mm2 csa cable if its more than a meter or so for a 3kw inverter. On 24v its half that (but prob use 75mm2 as its a standard size & will give less losses).

[Justme]

Even on 240vac you still make it when you can & store it till later.

[daftlad]

I know, I know, but i cant live soley on 240v, I have to make and store some for those quiet moments when I dont wish to hear the genny running or when I want the bathroom in the middle of the night.
This is where the problem is at. How to make and store it.
ok, I could make it as 240v but as ive already found out, a decent genny is beyond the budget. Im advised that the cheaper chinese ones arnt worth having as they die young.

Amy I think you would agree that your grasp of lectrics is less than total.
I think you have got the wrong end of things.
If you have a big pile of batteries wired together to give 24 volts, you connect an inverter to them (not a grid tie inverter which is different) which converts 24 volts dc into 240 volts ac, you then connect the entire 240 volt wiring system on your boat to the inverter and hey presto you have a boat wired for 240 volts ac running off batteries. All that is left to do is charge the batteries when they get low.
Basically you need to think in watts so if your washer uses 400 watts then that is 1.666 amps/ hour at 240 volts but at 24 volts it is 16.666 amps/ hour which is what your batteries will have to provide every time you wash your undercrackers.

I hope this makes things a bit clearer.
ta ta

[biff]

hi amy.
      d,is is intrestin stuff.i can imagine you deep in the bowels of your boat,kitted out in baggie overalls,boilermakers cap and pencil behind your ear.
       everythin should be working out perfect except for the confusing issue of vac and vdc,
    the good thing,the positive thing is that you have exellent advisers,all you have to do is take the time,,,(put the kettle on) ,,sit down and figure out exactly what you want.justme said it,, 24volt should be ideal.loads of compatible toys.which you can get of 24 volt heavy duty commercials at the rite money. ,,
and,,and believe it or not,,pj of the bog hotel fame is now running in the local council elections.
           biff

[PhoenixAutosport]

Well after doing some more research and reading the comments on here I have ditched the idea of a vehicle alternator due to the speed they work at being far to high for an economical generator and their regulation being simplistic to say the least, so I am now looking at using a permanent magnet generator like would be used on a reasonably sized wind application as this will work at much lower rpm and have a lower rotational mass so easier to drive, to get the most from it regulating the output with a maximum Power Point tracking circuit, this should hopefully mean a good output from a very small engine

[johnrae]

Amy,

Something else you need to think about - unfortunately.

And before you lose the rag with us please appreciate that we are not intentionally brow-beating you for enjoyment, we are simply trying to assist you with pit-hole avoidance.

You are talking about rigging up a bank of 12 volt batteries in parallel using 10 x 115AH rated units to give yourself a capacity of 1150AH at 12 volts

When considering recharging wet acid batteries you need to appreciate that it is the current flowing into the battery, not the voltage across it, that performs the charging process.  Consider this the inverse of taking power out of a battery, viz it is the current taken out that does the work, not the voltage across the battery.

The problem you need to address in your proposed arrangement is the means by which you ensure each battery gets the correct level of charge current.  Unfortunately, because of differences in battery chemistry and performance (no two batteries are identical) the amps will not be distributed in a balanced manner between all your batteries.  One or more will preferentially take the bulk of the charge current and will continue to do so, even when fully charged.  As a result not only will they become overcharged (and damaged) but will starve the other batteries of charge.  These starved units will hence be undercharged and, as a consequence, will possible become "sulphated" and loose their capacity.

If you insist on going for a 12 volt system then you need to look at purchasing batteries of the correct AH capacity which does not entail connecting batteries in parallel.   In other words you are looking for a single battery rated at 1200AH.  This, you will not find, but what you will find are 2volt cells rated at this capacity, and you will require 6 of these wired in SERIES to produce the desired 12 volts.  Such cells can be acquired second hand from your friendly forklift truck service man.

And finally, for the moment, if you get the chance I'd suggest you might want to avoid lead acid batteries and go instead for NIFE type (Nickel Iron) or similar type units.   These use an alkaline electrolyte, are more tolerant to deep discharge, are tolerant to being left discharged, are generally more robust and require far less maintenance (topping up) for the type of operation you intend.   An added benefit is that terminals and wiring don't corrode like they do on lead acid.  If you do go down this route do NOT use the same hydrometer that you might have previously used in a lead acid battery - the chemistries do not like each other.

jack

[Amy]

Jack

This is a battery description, can you tell me if they are suitable please

The manufacturer describes these as heavy duty 115 Amp/hour, lead-calcium, batteries specifically designed for severe cycling applications such as car carriers, recreational vehicles, refrigerated trailers, commercial-marine, coaches, and school buses.

The dimensions are quoted as: 13.0 in. (330.2 mm) L, x 6.8 in. (172.0 mm) W x 9.5 in. (240.3 mm) H; Maximum ambient temperatures are 125°F (52°C) continuous and 167°F (75°C) intermittent.

I have also extracted the following details from the manufacturers data sheet:


•Built-in flame arrestor prevents flame entry from outside sources,
•Built-in hydrometer indicates state-of-charge at a glance,
•Finger grips enable easy handling,
•Generous electrolyte reservoir helps prolong battery life,
•Plates are made from high-density paste,
•Wrought lead-calcium grids are fine-grained, strong, and provide corrosion protection,
•Spin-sealed, stainless terminal studs,
•Heat-sealed cover provides maintenance-free protection with strength and rigidity,
•Polypropylene case with reinforced end walls provides maximum strength,
•Liquid/gas separator prevents unwanted electrolyte loss,
•Extrusion-fusion intercellular connections provide increased performance and reliability,
•Separator envelopes prevent shorting between plates and misalignment caused by vibration.

[Amy]

Thank you Jack for your most eloquent and well described explaination. I greatfully appreciate the frightful task you have undertaken in trying to aid my education and I promise I shall do my upmost to make the most of your kind endeavours. I will have to put the kettle on and read a few more times to fully understand it.

Amy,

Something else you need to think about - unfortunately.

And before you lose the rag with us please appreciate that we are not intentionally brow-beating you for enjoyment, we are simply trying to assist you with pit-hole avoidance.

You are talking about rigging up a bank of 12 volt batteries in parallel using 10 x 115AH rated units to give yourself a capacity of 1150AH at 12 volts

When considering recharging wet acid batteries you need to appreciate that it is the current flowing into the battery, not the voltage across it, that performs the charging process.  Consider this the inverse of taking power out of a battery, viz it is the current taken out that does the work, not the voltage across the battery.

The problem you need to address in your proposed arrangement is the means by which you ensure each battery gets the correct level of charge current.  Unfortunately, because of differences in battery chemistry and performance (no two batteries are identical) the amps will not be distributed in a balanced manner between all your batteries.  One or more will preferentially take the bulk of the charge current and will continue to do so, even when fully charged.  As a result not only will they become overcharged (and damaged) but will starve the other batteries of charge.  These starved units will hence be undercharged and, as a consequence, will possible become "sulphated" and loose their capacity.

If you insist on going for a 12 volt system then you need to look at purchasing batteries of the correct AH capacity which does not entail connecting batteries in parallel.   In other words you are looking for a single battery rated at 1200AH.  This, you will not find, but what you will find are 2volt cells rated at this capacity, and you will require 6 of these wired in SERIES to produce the desired 12 volts.  Such cells can be acquired second hand from your friendly forklift truck service man.

And finally, for the moment, if you get the chance I'd suggest you might want to avoid lead acid batteries and go instead for NIFE type (Nickel Iron) or similar type units.   These use an alkaline electrolyte, are more tolerant to deep discharge, are tolerant to being left discharged, are generally more robust and require far less maintenance (topping up) for the type of operation you intend.   An added benefit is that terminals and wiring don't corrode like they do on lead acid.  If you do go down this route do NOT use the same hydrometer that you might have previously used in a lead acid battery - the chemistries do not like each other.

jack

[mespilus]

Have a look at this as well:

http://www.smartgauge.co.uk/batt_con.html