# Inverter to warm motorhome while driving?



## 93902 (May 1, 2005)

Hi all,
My Hymers heater is no good for winter travel. Would it be possible to use 2 110amp Leisure batteries with an inverter (say 1000w?) to power a fan heater of about 400w or 800w or would it flatten the batterys in no time?

My Dad recons I'd be better off running a Honda genny in a box on the scooter rack. Would this be possible?

PS. I'm new to forums so I hope this is ok
Cheers Phil


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## Drummer (May 9, 2005)

Welcome to the site, PhilD.
Anyone with a Hymer can't be all bad! 
Sorry about the heaters inadequacy, I thought Hymers were the dog's doodahs. I may have to reconsider!!! Will keep my eye on this one :lol:


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## DABurleigh (May 9, 2005)

Phil,

It is certainly possible, however rare, provided steps are taken to maximise the current from your alternator to the inverter. For an 800W heater you would need around 75A, whilst leaving enough to power headlights, demister, etc., so you are probably talking a heavy duty alternator if you don't have one around 110A output fitted already.

Then there are a couple of ways to go, the simplest being 35mm2 welding cable from alternator, via a heavy duty split charge relay or contactor, to the inverter and leisure batteries. High current cable runs should be as short as you can make them.

Or fit a high output alternator to battery digital regulator, most of which require a separate wire connected to the internal guts of the alternator. Sterling do a version where this is not required.

Again, a genny in a rear box will work, provided you think about air supply and exhaust, refuelling, etc, but it is a strange solution!

More common would be to fit a 2nd heater matrix to use heat from the engine, or a separate diesel-fired heater such as Eberspacher, or going low-tech, cab curtains and warm clothing, once you are certain you don't have a fault with your Hymer heater.

Dave


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## 88781 (May 9, 2005)

We had the same problem whilst driving along, the cab heating is not designed for large motorhomes so we bought one of these and changed the plug to suit the 12v in the rear...marvellous!

http://www.mflgadgets.co.uk/motoring.htm

Regards M&D


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## DABurleigh (May 9, 2005)

Fine, that's only 17A. Though those away from site hookups would still want to check they were sticking a decent charge into the leisure batteries as well while motoring.

Dave


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## Anonymous (Nov 10, 2000)

M&D

Looks good, but be careful if using on a cigarette plug, it will draw about 17Amps 

Ken


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## 93902 (May 1, 2005)

Thanks for the interest everyone. I thought I should add that the curtains drawn behind the seats works, but don't the kids just moan when we do that. lol
I've seen the diesel heaters Dave and it's the best way I think, but the cost is high and we thought the honda genny would have other uses the rest of the year. I like the Honda EU20i and maybe would be very quiet if we ran it in a well vented box. Maybe quiet enough not to upset others on sites?
Phil


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## Road_Runner_644 (May 9, 2005)

We run a 1000w fan heater in the middle of our 1996 B644 when travelling in colder weather. It runs through a 2000w invertor, via 2 x 120AH batteries, and the hymer panel suggests that about 15-20 amps is being put back in to the batteries by the alternator. As the fan heater switches on and off, its not a continuous cycle, and we haven't had any battery power problems. the heater pulls the batteries down to about 12v and they tend to sit there until the heater switches off, when they soon shoot up to 12.6 - 12.7 again, at which point the alternator backs off to about 5 amps or less. I guess if i took the thing down to the auto electricians i could get them to squeeze more amps into the leisure batteries, by modifying the split charge circuit.

The reason for the heater was the same, i couldn't believe how cold the thing was when we travelled. The kids were putting their coats on, and complaining. I looked for draughts, and poor seals, but finally found out the culprit was the roof vents, which literally just suck the heat out of the vehicle.

The cab heater is ok, but the heat was not being retained in the vehicle.

I never found this problem in our old CI granduca, as when you shut a roof vent, it was completely shut and air tight.

However these vents have some permanent ventilation even when shut, which i suppose is a safety feature, but a great annoyance. Even when parked, in high winds you can feel the air disturbance around them. 

I have sealed the ventilation slots in the lower part of the vents with a sliding plastic louvre thing that i bought at the local diy shop, but plan to seal them up in some more permanent way in the future. I'll find some way of manually allowing some ventilation when parked, thats what we were always used to. 

Dave


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## 93902 (May 1, 2005)

This sounds great! I take it you have just joined a second leisure battery to the existing leisure battery(?) then connected the inverter to one of them, presumably with proper battery terminal clamps rather than the cigarette lighter plug which comes with smaller inverters?

I've read in Practical Motorhome somewhere where they fitted a device which dramatically increased the power going to the leisure battery from the engine. This did not need any messing about with the alternator. Perhaps one of these would keep things topped up? Has anyone heard of this device?


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## 88941 (May 10, 2005)

Invertor to warm a motorhome !!!!!!! 

it will never work you'd need loads of em to produce that much heat... my invertor runs pretty cool really.

Keith n Debs...... :lol:


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## 91929 (May 1, 2005)

Inverter to produce this power would also produce a fair amount of heat itself

If you can afford it a deisel heater is probably the best & you can leave it on after breakfast & keep it on while travelling

They work great output - up to 3kw depending on model & make
They can also operate as a home central heating system to a preset temperature


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## DABurleigh (May 9, 2005)

> This did not need any messing about with the alternator. Perhaps one of these would keep things topped up? Has anyone heard of this device?


Phil,

This is the same to which I referred in my first reply to you:


> Or fit a high output alternator to battery digital regulator, most of which require a separate wire connected to the internal guts of the alternator. Sterling do a version where this is not required.


It is a Sterling Alternator to Battery Charger:
http://www.sterling-power.com/htm/ab1290.htm

Dave


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## Road_Runner_644 (May 9, 2005)

Phil

in my setup, the original battery was removed, and 2 matching batteries were installed under one of the dinette seats. The invertor is installed beside them on a short fat cable to cut down the voltage loss.

I've just looked at Dave's link to the advanced alternator regulator and i like the idea, as in theory, whenever i am using anything that pulls 4 or 500 watts or more, the charge from the alternator is not covering it. 

I'd love to get a diesel heater fitted, but they dont come cheap.

Dave


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## 89905 (May 1, 2005)

hello roadrunner 644
we run a hymer S670 and before that a S555 The cab heating isnt to bad on a run sounds to me like you need to flush out the heater matrix .
all the best 
Twodogs


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## Anonymous (Nov 10, 2000)

Hi Dave,

[/u][/i]Quote from Sterling

On completion the unit switches off, and the process continues as a conventional split charger system 10, if however the domestic battery falls below 12 volts the system will auto restart and continue the process again.


This means that the battery has to be discharged before the advanced battery charger will kick in again,

(11.8 volts = a discharged battery, thats if you dont want to speed up the sulfation).

If you have a 2kw inverter connected and you are drawring only 1 Kw through it, you will be drawing around 70 amps from your battery until it reaches 12volt,

What this does is 1/ possibly heat up your battery 2/ make the battery complete a full cycle.

A batterys life can be measured in cycles ie from full to empty and back to full again.

An alternative system does not wait untill the battery is flat but maintains the battery at its fully charged voltage (or trys to), this means the the charging system does not wait until your battery is flat, as soon as there is a voltage drops the alternator kicks in and takes up the load so that there is no discharge from the battery.

This I think is a better system for what you are doing.

see adverc

Doug...


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## 88724 (May 9, 2005)

Hi Doug

on conventional split charge system if there is a load at the leisure it will supply more ampage (to its limit) a split charge is still putting 13.8- 14.2 v into leisure measure one and see. The other important point to note is that its like a split charge system is a figure of speech and does not mean that its a two way street powr wise.

ie it (The Sterling unit) as not stopped being a supply and therefore is not running the battery down awaiting a new Charge cycle.

George


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## Anonymous (Nov 10, 2000)

HI Goerge,

I must be a little thick tonight as I am having trouble understanding your text, can you do a re-write with a little bit more explanations.

I dont see where the diode splitters come into it, Yes I know that when the Sterling charger in its off cycle the system reverts back to the alternator machine sensing control.

If the alternator in the machine sensing mode is not capable of supplying all of the power required by the inverter then the battery voltage will drop down to 12 volt at which time the sterling controler will kick in, increase the alternators output and recharge the battery. ie 1 cycle.

Or are you talking about somthing else completely, sorry

Doug...


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## Road_Runner_644 (May 9, 2005)

Acknowledge the point about the heater matrix Twodogs, i suppose it would be wise to check it out, but the heater does seem reasonably good. Its these hymer roof vents that i blame.

And Doug

What i thought i was reading in the text on the sterling page, was that the advanced regulator would kick off dumping 70+ amps into the batteries if they were well down in charge. But it wouldn't keep this up based on the readings it had taken and guessed the total ampage of the batteries.

I would expect it to kick in if a load was placed on the batteries, just like a normal regulator, but i admit i'm a bit puzzled by the "timed cycle" bit, stating that it would turn off, and start all over again.

It seems daft that it could be "tricked" though, it says constant monitoring, so maybe it has a rethink if theres a sudden pull on the batteries.

Isn't it great when intelligence is applied to these little electrical thingy's

I'll give them a ring before i buy one to check it out.

Cheers

Dave


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## 93902 (May 1, 2005)

Hi twodogs


twodogs said:


> hello roadrunner 644
> we run a hymer S670 and before that a S555 The cab heating isnt to bad on a run sounds to me like you need to flush out the heater matrix .
> all the best
> Twodogs


This is also a must try. I've only had my S555 since June 04 and we used it every moment we had! I'm now looking at the few minor problems like the heater before we set off again in April (when I my holls reset.)

BTW everyone, I've sacked the genny idea. I dont think I could enjoy my stay on a site knowing it was running, however quiet!!!

I wish I was better with electrics, I'm soon lost. (sorry Dave)
Phil


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## 88724 (May 9, 2005)

Hi Doug

the text you refered to said it would revert to "split charge" like operation after charging cycle completed.

At this point the alternator will be supplying 13.8v to 14.2 v under its normal operating position, this means that the battery will be being supplied via the alternator (with as much power as the alternator is capable of) and not be dropping the battery down to 12v 

It is not the same as "split charge" in that you would not lose charge to the starter side like a split charge system does (Do not ask, I have not got time to explain this again, last time it ran to about 15 pages)


George


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## 89013 (May 11, 2005)

Hi Phil,

I have had the same problem with my Autoroller (7 berth, so big living area to heat). We just couldn't get the heat from the cab to the rear, and the Fiamma vents have a permanent ventilation facility, which is a pain on the move in winter.

So I have now installed a second heater matrix & fan unit (from CAK Tanks) - I have plumbed it in parallel with the cab heater. It was a bit unnerving, since it came with no installation instructions. I have also fitted Fiamma thermal screens. 

The new setup seems to work a treat, although we have only taken it about 50 miles so far. We shall see at half term how it works for real.

Good luck with whatever you decide.

Nick


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## 93902 (May 1, 2005)

Hi Nick,
Didn't know cak tanks did anything like that. I was thinking of a rear heater out of a Nissan Serena. 
I'm sure the roof vents are a major part of the problem. Mine has an extra one above the overcab bed and it's leaking from time to time.
Doh, if only I had 50 grand spare, it would save me days of work!!!
Cheers Phil


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## Anonymous (Nov 10, 2000)

Hi George,

We are obviously talking from different levels of experiance so lets drop it.

regards Doug...


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## HookyHymer (May 1, 2005)

Hi Phil,
Regarding the original problem of the heater not being very good, I had the same problem on mine, I found that the flyscreen mesh inside the entrance to the air inlet trunking in the bumper was completely blocked with mud & sticks, took the mesh out and washed it, the heater is now more than good enough.
Worth a look!
Regards
Glenn


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## 88974 (May 11, 2005)

Hi,

Am I doing things wrong, we run our hot air heating system whilst we are driving, this is run of the bottle gas and it heats a boiler, should we not be running this whilst moving. we also run the fridge on gas all the time as well (even though it is a 3 way fridge) as we find it works better.

Would be glad to know if what I am doing is dangerous.


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## 93819 (May 1, 2005)

*heaters*

hello kildare

i am not techie so may be wrong about this but i am sure my boyfriends response to using the gas bottle whilst driving would be

Noooooooooooo!

i am sure you will have a proper response soon

paula


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## 89193 (May 16, 2005)

hi kildare

i think you'll find that running your gas appliances whilst travelling is not only dangerous but illegal.

secondly why use gas for your fridge all the time ? if you'r on hook up you've already paid for the mains so use that rather than your gas


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## Anonymous (Nov 10, 2000)

If I remember correctly this point of using gas whilst on the move has been raised before, on that occasion I looked through my M/H book and could find no reference to not using the gas fire (carver) when under way, the point was put by other forumers (if there is such a word) that the gas should be turned off whilst moving for safety reasons, but it’s not turned off for gas driven vehicles, and liquid gas drawn from the bottom of the tank is far more dangerous than that drawn from the top, so surely that negates the reason for turning off at the bottle?

I accept the reasons for not having naked flames on petrol station forecourts.

Is it illegal to have a gas appliance working whilst driving?

My own instincts say no don’t do it, but I think I would be hard pressed to win an argument on it

Ken


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## 88724 (May 9, 2005)

Hi all

Running Gas appliances while driving is not only safe it is also legal.

On my Iveco the 3 way fidge was never used on 12v when driving it was always un on gas, 12v Freezes you milk etc as the 12v part is not themostatically controlled.

There are two places were they do not want you running gas appliances

Garage forecourts and Ferries, on the forecourt the chances of fuel vapour reaching the flame for the fridge is HIGHLEY unlikely, I and many others never switch the gas off on a forecourt.

Example of another URBAN legend Cell Phones, Anybody see the weird science program they filled a caravan with Highley flammable liquid and had about 5-6 phones ringing in there on vibrate and everything, then they finally blew it up by using static off a chaps clothes !!

The eberspacher and gas heater Myths are just as bad, consider eberspacher exhaust hmmmm, now think car exhaust do we have to switch our cars off and roll them to the pump? On older cars how many of us have had to replace faulty spark plug leads why have none of these ever caused a forecourt fire ? Why can a tiny flame on fridge which is well shrouded cause a fire yet an exhaust belching sparks and flames doesnt.

Many of us will remember the pump attendants smoking and filling cars up.

Nanny state, Hollywood and urban legend again.


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