Volts drop

BadlyOverdrawnBoy

When we first got the van (Autosleeper Topaz) we noticed flickering lights when operating the water pump, which I put down to duff-battery-itis, and replaced the battery after last winter's trip to Morocco. However, the trouble has continued after replacing the battery this summer, and is more noticeable since I have started using the laptop. So I did some measurements after getting back and was quite surprised when under the load of 4 lights and the Propex fan, the measured volts drop between the battery and the fuse board was 0.74V. This is without 2 major power consumers, i.e. the water pump and the laptop. I think the Propex has a low volts cut-out because it tripped in the mountains in Morocco - BRRR!

Does anyone have any idea what kind of volts drop is normal or acceptable?

johnsandywhite

Hi BadlyOverdrawnBoy. This should help you to calculate the losses

GeorgeTelford

Hi

Depends on who you talk to, I always aim for 3 % max or sub .39 volts and will always better that if I can.

The problem is that most manufacturers underspecify the wire/cable in vans, whether its because they are being Cheap or just dont understand what they are doing who knows ( But probably the latter, because the savings in weight and cost are minimal)

I wonder what your total losses are when you had the fuse to appliance loss too!

BadlyOverdrawnBoy

That's what I suspected, George, and the run to the Propex is even longer with thinner cable. As you say, the cable won't be expensive to replace but routing it will be a real pain. Better to do it right in the first place.

GeorgeTelford

Hi Bad

The worst one's are the lights, these are the most noticeable due to the flickering and usually the worst to replace.

Sometimes its easier to run a new cable in addition to the old one, pulling an old cable through CAN occasionally damage other wires in that part of the loom.

gaspode · Moderator

It sounds to me as if you have a high resistance connection somewhere, probably on one of the major junctions such as a main earth connector or the battery terminal connectors. Dismantle and check all connections carefully, it's probably worth fitting new battery terminals and replacing any earth straps.

PamNPete

Iee Regs used to be 1% +1v (2.3 = 1 = 3.3v) when I ws teaching (now retired some 5 years) and they have been those values for the past 60 years
For supply cables

So you should not get so much within the van

GeorgeTelford

Hi Pete

In the IEE 16th Edition Voltage drop is permissable to 4% Below is a the electricians guide to the 16th Edition wiring regs.

MandyandDave

It's also worth checking for consumption with everything turned off, in case of leakage somewhere..

Regards M&D Smile

PamNPete

Well George i did say earlieert hat it is some time since I left teaching electronics and there have been several changes in the regs.
Quite a few since they introduced the solid cables as opposed to the 3/024's etc

So they must have slackened the regs on the supply volts drop

Condouctor voltage drop is still completelt different to that across componetns such as light bulbs
Conductors have to have minimum volt drop whereas components will have the whole of the available voltage dropped across them - particularly light bulbs and heater coils